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Indeed, there can be little doubt that tactile experience had sexual connotations well into the Numbness modern era. When the characters of the decid- edly earthy Shrovetide plays spoke of liking to Before the advent of modern diagnostic tech- feel a woman they had more in mind than the niques e. These substances had narcotic as well as anaesthetising effects, however, and were rarely used to make the body completely insensitive to pain.
It was difficult to calculate the correct dos- age, and many experienced surgeons considered the risk that the patient might not wake up from this artfully induced unconsciousness to be too high. For a long period in time, loss of sensation was considered treatable by some and incurable by others. Before the late 19th century, however, the art of medicine was usually at a loss in cases of blocked nerves, or damaged neural tissue. The taming of touch 18th century pedagogues, for instance, regarded the tactile sensitivity of the blind as particularly worthy of emulation.
Rousseau advised against children to become too used to heavy manual work, since their hands would become calloused and lose their fineness of touch . He thought it essential to preserve this sensitivity so they would be able, for example, to identify objects by their feel in conditions of darkness. Leonardo Arte, Cremona, meticulously clean in order to maintain the sense of touch.
Medicine has long abided by certain proto- interpreted either as a localised injury to the cols in respect of the touching and grasping of part of the body in question, or as a symptom another body. By the early 19th century, however, or side effect of a serious illness e. Nevertheless, in the s, the looked not only for tell-tale changes to the sur- renowned physiologist Hermann von Helmholtz face of the skin but also tested its sensitivity by still regarded pulse-taking as the inserting a needle into the calf or middle finger. Any numbness in the suspected patient was Since the 17th century, the sense of touch regarded as signa univoca, a clear symptom of had gradually been excluded from the act of the dreaded disease.
Although local anaesthetics eating. Only bread continued to be eaten with were not introduced into surgery until the end the fingers in polite company. All other food of the 19th century, the pain-numbing effects of required the use of a fork. Haptic perception: an historical approach 9. Michael Tritsch, Dsseldorf, The statistics for skin diseases became the basic equipment of a lower-middle which are available for some countries report no class kitchen, while working-class families largely abnormal increases in loss of dermatological sen- continued to eat with knives and spoons.
They sitivity that might indicate a rise or reduction of probably used their hands as well . According to a sta- tistical report by the American Dermatological Association, there were only 56 cases of anaes- The deterioration of tactility thesia total loss of sensation in the USA in the period between and These ed territory. There is no historical research on two dermatological and neurological conditions the subject. Karl Marx already noted that the represent a bare 0. Neverthe- less, machines could not replace much heavy and hazardous manual work, so that calloused Discovering the physiology of haptic hands undoubtedly continued to be a charac- teristic physical feature of the industrial and perception manual worker as the 19th century wore one.
But touch is not simply localised in the hand. Did the The first physiologist to undertake a systematic long-term changes in the world of life and work experimental investigation of the sense of touch technologisation, industrialisation also lead to was Ernst Heinrich Weber Fig. Gustaf Blix in Sweden and Alfred Goldscheider in Germany demon- strated that the skin contained both temperature and pressure points by subjecting tiny areas of skin to electrical stimulation . Sensorial circles was Webers term for highly sensitive areas of the skin.
He thought that their anatomical substratum was the skin nerves and assigned a particular nerve to one or more of these circles. He also noted that, when applied the points of a pair of compasses to the skin, the pricks could not be experienced as two distinct sensations beyond a certain distance. This marked the discovery of a phenomenon described towards the end of the 19th century as the simultaneous space threshold by Max von Frey , who was a pupil of the cel- ebrated Leipzig experimental physiologist Carl Ludwig As late as the s, physi- ologists were still using Webers compass to mea- sure the sensitivity of various areas of the hand.
Webers pioneering exploration of the sense of pressure led to the law of just-noticeable dif- ferences being named after him Webers law. The role Bosch Stiftung of the so-called pain sense, which can also be localised on the skin, was relatively minor, for he lumped pain together with the common sense, early stage that pure sensation tells us nothing about which it was impossible to obtain scientifi- about where the nerves that produce the sensa- cally exact information. His famous treatise Tastsinn Knowledge of the fine structure of the skin und Gemeingefhl Sense of Touch and Common was sketchy at the time Weber began his experi- Sense, not only included important research ments.
Although the vital importance for the results in the field of physiology of the skin but perception of vibrations of the large, lamellae- also gave a boost to sensory physiology in like corpuscles at the end of the nerve fibres of general. Terms still used today in physiological the subcutis Pacinian corpuscles was already research, such as threshold of stimulation, tem- recognised, their functions as receptors was perature sense or simultaneous spatial thresh- still a matter of debate.
So it was not surprising old, were either first coined by Weber or named that Weber should continue to assume that the after his experiments. Haptic perception: an historical approach In , he proved the existence of pain points. In doing so, he added a fourth sense to the senses of pressure, warmth and coldness. A year later, he discovered that each of these four forms of sensation or modalities possessed its own organ. The so-called Krause-Endkolben Krauses cor- puscles , for example, were responsible for the sensation of coldness.
It consisted of a series of brushes of different degrees of stiffness which were fixed instruments developed by leading 19th century with sealing wax to a movable rod Fig. This sensory physiologists produced results that are instrument, known universally in physiological still valid today. The experiments performed on prisoners Towards a haptic age?
The Italian psychiatrist and crimi- was not just referring to a trend in underwear. To test the for healers with magic hands magnetopaths, reflex responses of his human guinea pigs, he masseurs and chiropractors and the supposed- stuck needles into them and treated them with ly growing numbers of adults in need of loving electric shocks, and must certainly have left sex. For years before this, the German weekly them with more than merely unpleasant sensory Die Zeit 11 April published a Manifesto impressions .
In contrast to earlier times, it is now sceptical, pointing out that similar trends can no longer the individual senses that are enumer- be observed in previous times. In the first half ated and classified, but sensory perceptions of of the 20th century, for instance, some thinkers all kinds. The interpretation of the sense of touch were maintaining that the sense of touch was as a skin sensation consisting of a number of losing its significance in sensory knowledge, discrete aspects pressure, heat, cold and pain while others were insisting on the priority of may be regarded as typical.
The methods and haptic experience. The Hungarian psychologist Geza Rvsz cathode rays which produced television images took an opposite view. In the early actually stroked the retina of the eye. Hence s he stressed that knowledge acquired by the title of this famous book The Medium is the means of the sense of touch was more convinc- Massage . Today, in the multi-media ing and persuasive . Moving forward to the age, McLuhans dictum has acquired new associ- philosophy of the present, we encounter Jean ations: our continuous zapping between dozens Baudrillards theory that the hand is no longer of channels provides plenty of exercise for the the prehensile organ that focuses effort: rather, sense of touch.
The invention of touch enable their grasping hands to be controlled screens, interactive monitors which dispense with greater precision. Nevertheless, the sense of with the keyboard and mouse, making comput- touch continues to be a headache for scientists ers easier to use than ever, would appear to working in virtual reality and robotics, since this bear out Baudrillards theory that the increase sense is not located in a particular organ but of tactile experience in the media age has not spread over the whole body.
The invention of necessarily produced an enrichment of sensory the sensing glove by Scott Fisher in was an perception. In the face of the increasing lack of important milestone on the way to cyberspace. A simple and inexpensive version of this glove is It addresses the growing need for a kind of close- now available as a computer toy . The data ness and togetherness that might compensate suit, with its armoury of pressure- and tem- for the negative aspects of high-tech society.
He perature-sensitive sensors, represents a further sees the rapid growth of self-help groups and the development of the glove. Although this suit has worldwide boom in new systems of learning and so far not been put to any practical use, it is occa- therapy e. On the other hand, the late s witnessed the beginning of a remarkable Look into the future rediscovery of the sense of touch.
For it was around this time that a generation which had What will the future look like? Haptics are not grown up with television began to discover that, only to be put to recreational e. Scientists are working sight, there was also a sense of touch. Besides on sensitive prosthetics allowing for example, the sit-in, the flower-power generation and the the restoration of grip function in patients with hippie movement also invented the touch-in, at spinal cord injuries.
Thus, according to James which people who had never met before would Geary, haptics research will certainly extend the kiss and embrace and seek to offer each other human hands reach, across biological frontiers tenderness. The interpretation of the sense of touch as a skin sensation consisting of a number of discrete aspects pressure, heat, cold and pain may be regarded as typical.
The methods and instruments developed by leading 19th century sensory physiologists produced results that are still valid today. Selected readings Bhme H n. Der Tastsinn im Gefge der Sinne. Exploring the senses in history and across cultures. Summary Ausstellungskatalog.
Kunstverein Bad Salzdetfurth, The idea that perception or sensation may be Bad Salzdetfurth localised in certain physical organs e.
Human Haptic Perception: Basics and Applications
Deutschland ed Tasten. Steidl, Gttingen The system of sensory physiology of which Loenhoff J Die kommunikative Funktion der touch is one important element is shaped by Sinne: theoretische Studien zum Verhltnis von the influence of both medical thought and the Kommunikation, Wahrnehmung und Bewegung. For the western eine kurze Geschichte der Palpation von den Anfn- tradition the Greek philosopher Aristotle gen bis zur Gegenwart. Steiner, Wiesbaden BC is of utmost importance.
Spektrum Akad. The Aristo- Krpers in der Feeling Therapy. Junfermann, Pad- dent nature of the sense of touch was scarcely erborn, ever questioned in the subsequent centuries. The pioneering experimental sensory physiol- ogy of the 19th century is characterised by the definition of the senses according to sensory modalities. Introduction the human sense of touch and deserve, at least, to be mentioned here: G. Fechner, W.
Wundt, The science of the human sense of touch, also J. Czermak, L. Mach, known as haptic, had a long and rich tradition O. Funke, H. Lotze, E. Hering, G. Meissner, T. Philosophers Hausmann, P. Mahner, A. Goldscheider, G. Bre- and physiologists, medical doctors and psy- cher, O. Scheuer, R. Weber part of the knowledge we have today. Among these scientists are some whose works about The scientific and systematic examination of the research into the sense of touch were inter- human sense of touch began with an anatomist nationally known and influential while others, and physiologist from Leipzig, Germany, Ernst though, were only received in the German speak- Heinrich Weber He studied in Wit- ing world.
Regardless of this criteria, several of tenberg and Leipzig and became professor of the most important representatives of German comparative anatomy in in Leipzig and, touch research before World War II and their in , professor of physiology. In , he scientific contributions are outlined below. The laid out first findings about the systematic and accounts are ordered chronologically accord- experimental testing of sensory thresholds in the ing to the respective year of birth E. Weber, human sense of touch in his dissertation paper, M. Dessoir, G.
Rvsz, D. Katz, and De pulsu, resortione, auditu et tactu annotatines E. In creating this list, an exem- anatomicae et physiologicae . As early as this plary selection was made which can only include paper, his findings about two-point discrimina- a part of the range of German scientists who tion were developed and he could prove that have researched the human sense of touch in the the ability to discriminate between two tactile last years. A comprehensive presentation is stimuli, applied at the same time on two points of impossible in a work such as this and must be the body, was different in different places on the left for a historical-psychological study.
The fact, skin. To show this, E. Weber used a compass however, that such a work does not exist even in with dulled points. The sensibility thresholds a most basic form shows that the history of this valid here are used still today as a diagnostic research is not exactly the focal point of todays tool in, e.
Weber continued to scientific interest. Several authors are neglected explore the subject of the research of the human in this sketch partially, because their effects sense of touch even after his dissertation. The are sufficiently known and acknowledged and central results of his work regarding the sense partially because, to date, too little information of touch were published in a short, German-lan- is to be found about them. In any case, other guage abstract in . As a result, practical considerations and the hope of discovering basic principles of other perceptual modalities were the main aim of his experimental studies.
He didnt use only experi- mental findings for the foundations of his studies of the sense of touch but, as was usual in his times, phenomenological and generally formu- lated arguments found their way into his presen- tations and analyses. In this way, he confronted the basic dimensions of human perception while, at the same time assuming that, for inexplicable reasons, the soul is forced to process all sensa- tions in relation to the categories of space, time and quantity.
With these categories E. Weber laid the foundation for the interpretation of his own findings about spatial two point stimuli dis- crimination. The time-space structure of our per- ception is, for Weber, a natural axiom although Kants philosophy may have contributed to this line of thought. At the same time, however, he postulated a sense of locality or feel for local- ity which appears to be all the more differenti- ated the more numerously nerve fibres are pres- ent in the various sensory organs.
Weber hypothesises that the sensory organs are separated into small, departments located next to each other and that they are connected to the Lehre vom Tastsinn und Gemeingefhl The Sci- brain with individual nerves. Weber depict- ence of the Sense of Touch and General Sensa- ed these areas of the skin as feeling circles  tion followed. Within, he presented several or sensation circles . The ability to differen- newer and older studies as well as a discussion tiate between two spatially different stimuli is, about the few national and international publica- according to him, based upon the fact that the tions about anatomy and the physiology of the two stimuli lie within two different sensation sense of touch that had been published at the circles.
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He also suspected that the nerve fibres time e. Bell, J. Weber did not pursue his research into to a topographically- ordered, corresponding the human sense of touch because of philo- area in the brain. As support for his hypothesis sophical considerations but, rather, as he briefly he presents results from observations made dur- stated in his publications from and , ing tests conducted on patients paralysed on one this sensory organ offered him the practical side of the body hemiplegia . At the same possibility to conduct the most varied of experi- time he points out that his hypothesises are ments and to collect data from various points of based on founded, yet non-proven assumptions view without damaging the human body while as the basic relationships between the paths of doing so.
In addition, Weber was hoping to col- the nerves related to the sense of touch and the lect information which he could later use [with brain had only been insufficiently examined thus respect to] the visual and other senses. German pioneers of research into human haptic perception During his studies he realised that pas- ence for hundreds of years and which the newer sive finger contact with objects of various sizes science, in its global form, was gradually getting resulted in an object recognition that was worse away from.
Weber presented indications which than when the objects were actively explored . This led him to the question of how postulated by E. Weber and its connection to much influence the muscular activities and the sensory activities of the skin become clear in accompanying pressure stimuli which affect the the following quote: The sense of locality helps skin have on the perception of touch in situ- us to better know the movements of our limbs ations such as weight estimation. The method- and with the help of the movements of our limbs ological difficulties that E.
Weber faced during dependent upon our own free will we get to these examinations were described as clearly as know our skin and orient ourselves on one and the the results which were gained by them. Both abilities, from the beginning Regarding the general function of the senses, extremely limited, compliment and complete each E. Weber wrote that all senses are created for other .
The lightest the number of nerves in each sensory organ. The slightest differentiate is much better formed in the visual change in temperature is as noticeable as the organs, with their high density of nerves, than smallest change in weights. We are able to deter- in the sense of touch. With precise methodology mine the position of our limbs precisely at any and academic system, he examined the spatial, time without the help of visual contact.
The qual- aligning discrimination of the skin and every ity and aligning discrimination of individual sen- possible part of the body with the help of his sory systems is, however, dependent upon how experimental paradigm of two-point discrimina- finely we are able to perceive the properties our tion. The results, which he presented in a table environment. The smallest sensation thresholds with values, showed him that the spatial aligning and the greatest stimuli-amplitudes to the point discrimination for pressure stimuli were differ- of painfulness determine the range and sensory ently precise from bodily part to bodily part.
In dimensions of our perception. As a scientist, it E. Webers terminology, the sense of locality is, was his concern to determine these dimensions as a result, unevenly precise in its development. Our sen- point-cues, but, in separate papers and essays, sory perception of the world is dependent upon outlines new phenomena and issues. These stud- the smallest measures which we possess and with ies, at descriptive-analytic and experimental lev- which we can judge time and space . In different chapters, providing that he was aware of them. While doing so, he sticks strictly to the that these volume changes could be responsible available data and facts he was not interested for the perception of warmth and coldness.
He in philosophical interludes or historical feuds. This, for mouth, lips to perceive temperature. He noticed, him, existed alongside the sense of locality among other things, that areas that were scarred and the sense of pressure and, together, these as a result of burning were less able, if at all, to three senses were the abilities of the sense of adequately judge temperatures and attributed touch. These terms do not, however, cover the this to the destruction of the touch organs.
He entire, complex reality of the sense of touch also pursued the question of whether inner and, for this entirety, he created another term: organs and mucous membranes are capable of general sensation. This word creation existed registering temperature sensations. He tested, in alongside the, at the time, widespread term experiments on himself and others, whether or common sense meaning coenaesthesis for not hot and cold water led to sensations in the the integrative and apperceptive performance of stomach or nasal cavities and he was not afraid the sensory apparatus.
These sensations, which of administering clysters with different hot or Weber called Gemeingefhle general bodily cold water temperatures. He observed that the feelings or common sensation include the left hand was much more capable of determin- consciousness of the state of sensation that is ing differences in temperature than the right carried to us from all of the body parts which are and attributed this effect to the difference in the connected by sensory nerves with the exception thickness of the skin.
He also described numerous of the specific sensory feelings from the nameable illusionary effects which appeared to be depen- senses themselves. He later writes, General dent upon whether the tested area was a single sensation is finest in the organs of touch and in finger or an entire hand. His explanation for such the muscles which belong to those body parts rich- effects was a summation of the impressions in est in nerves .
A central quality of general the brain . That human skin shows variance sensation is, according to this conception, pain in the quality and accuracy of warmth and cold and, as a result, the perception of pain became perception is, according to Weber, a sign of cor- a direct component of the research E. Weber responding organs in the skin organs which conducted into the subject. However, the Weber was obviously aware of the ambigu- anatomical research at the time was unable to ity of the term though and it comes then as no provide information about this and, as a result, surprise that he attempted to describe with E.
Weber decidedly left this question to future examples from clinical practice the ways that researchers so that they could answer these sensations of the sense of touch and those of questions more definitively . This open and common sensation are related to each other.
One honest reference to the need for future research example thereof is his description of an 18 year is to be found firmly formulated in many old shoemaker who suffered from hypochondria. Despite He was fully insensitive to strong pain stimuli the poor quality of the data available to him, being stuck by a needle or hot iron being placed he attempted to explain the observed effects as on his skin but was, however, able to feel the best he could with the existing knowledge.
In the lightest touch of a feather. He out it helping to make the terminology of haptic showed a limitation, rather a complete insen- studies clearer. Weber generated, with remained sensitive to touch stimuli on the skin scientific creativity, systematic and experimental of the affected area. He, for instance, gradually taken up again for many decades. He described, raised the temperature of water in which he sub- for example, the appearance of sensory illusions merged his own hands or the hands of test sub- after the amputation of limbs and several effects jects until it became painful.
He recorded and that illnesses in the brain and spine have upon presented these results as painstakingly as those the sense of touch especially the emergence of of a test in which he held a key which had been hallucinations. He devoted himself at length to cooled in quicksilver on various body parts for the question of in which ways the attention pro- seconds or even minutes.
Even the various types cesses changed the perception of touch stimuli of pain that resulted from these tests stabbing  and that elementary memory capacities are or burning pain were recorded in the protocol. These tests were con- which aspects self touch the touching of ones ducted using various weights which were tied to own body are dependent upon. Experts in various disciplines, contemporaries Alongside inner organs, mucous membranes and following generations of scientists research- and vessels, Weber was of the opinion that espe- ing the sense of touch and other sensory systems cially the muscles were responsible for providing were influenced greatly by E.
Wilhelm us with precise information about different quali- Wundt accredited him with the title The Father ties of common sensation. In this, he includes of Experimental Psychology but other anato- the performance that can be achieved when mists and physiologists also declared his works subjects judge the difference in weights of two as milestones in their subjects . That he was objects when the pressure stimuli are consider- quite aware of the interdisciplinary and strong ably removed. Also, we thank common sensation influence of his works can be seen in a program- of the muscles for the fact that we are always matic quote from a paper published in The aware of the active or passive position and study of senses is a point in which, at some time in location of our limbs.
According to Weber, the the future, the research of physiologists, psycholo- fact that we can do this with such precision and gists and physicists must merge . This suggestion was, however, made with great cau- Max von Frey tion  as he did not wish to expand the existing terminological framework within the study of the Max von Frey was born in Salzburg sense of touch. He could not have been aware and studied medicine at several German univer- of the terminological uncertainty that this word sities. Later he worked with Ewald Hering and would later cause.
He developed the von Frey hairs an exami- national instrument used still today to determine pressure points on the skin. To do this, von Frey used fibres of various diameters which first bend when a certain vertical pressure on the skin has been reached. With the help of this instrument, von Frey observed that the human skin has pres- sure points and that in their immediate vicinity no sensation of pressure can be created. In addition he was able to show that these key points are distributed unevenly on the skins surface.
The Wrzburger Physiological Institute, under his direction, was practically a synonym for physiological and psychological research into the sense of touch and was recognised for its strict guidelines of experimental methodology. The core of these studies was von Freys notion that the performance of the touch sense could only be measured and explained by studying the perception of pressure. For von Frey, the qualities of the sense of touch existed, for the most part, to make pressure and contact perception possible in Leipzig where he habilitated as a professor of and the perception organ existed exclusively in psychology in In he received an asso- the skin.
That contact and pressure could be ciate professorship and in a full professor- perceived even after the skin had been frozen or ship of physiology at the University of Wrzburg. In he began, at colleagues. As a result of his believing that no first with Friedrich Kiesow, to publish fundamen- pressure sensitive areas existed under the skin tal studies about the sensitivity of the skin and in contrast to the beliefs of Strmpell, Head and tactile sensors in the Zeitschrift fr Psychologie Sherrington von Frey acrimoniously managed und Physiologie der Sinnesorgane Journal of Psy- his line of argumentation.
In doing so he took chology and Physiology of the Sensory Organs. Especially impressive is von Freys argumen- tation when he attributes the perception of pas- sively led arm movements not to the effects of joint, tendon or muscle receptors but rather to the deformation of the dermal tissue under the affected joint. He noticed that the anaesthetis- ing of the skin over the joint led to a 1 loss in perception of the passively led arm movements in comparison to the same procedure with skin that had not been anaesthetised.
For von Frey, changes in the tension of the skin were the key to understanding minimal positional changes of the limbs. Slightly more placably, he suggested that other sensory tools may very well be at work in movements of greater scale . However, von Frey categorically rejected the idea that the joints or muscles contain recep- tors which also contribute to the perception of changes in position. Max von Freys essential contribution to touch sense research alongside his experimental test- ing of key points is his doggedness on the veri- fication of his theses an attribute which repeat- edly enriched the contemporary discussion with critical findings.
Without von Frey and his relent- less adherence to his theses the debate and the scientific evidence regarding a deep sense of pressure would certainly have been less fruitful. MAX DESSOIR In this sense, his misunderstandings contributed greatly to the expansion of the theoretical and practical basis of the research into the sense of was much better known to his contemporaries.
This is shown, for one, by his works reception in the USA where it was discussed vigorously . In this article, Dessoir sets himself the goal Max Dessoir of systematically working through all available experimental findings regarding the research of Max Dessoir is barely known among the sense of touch. In addition, he presents sev- todays scientists for his experimental studies eral of his own experimental and phenomenologi- into the sense of touch. The Berliner philoso- cal studies about the psychology of the sense of pher and psychologist is, at best, remembered touch.
These had been conducted, for the most today as an art scholar, pioneer of psychological part, in the Kniglich tierrztlichen Hochschule aesthetics or as the coiner of the phrase para- Royal Veterinary College in Berlin. His comprehensive paper About the Besides a distinct sensitivity for methodical- Sense of the Skin ber den Hautsinn  experimental questions, especially the analysis first written as a medical professorial disserta- of the sources of error, Dessoir strove for a clar- tion in Wrzburg and then published in Du Bois- ity in the definition of terminology.
He was apparently the first to sive of human organs received the name haptic explicitly address this problem of terminology, a term that even today is of practical and theo- the ever-present difficulty in integrating the large retical importance. He didnt know lications of examinations into temperature per- at the time that this would survive as his greatest ception, pain perception and that of electrical scientific contribution to research of the sense applications in which he was critical of the of touch Dessoir stumbled into the contempo- methodology used.
Especially the studies into rary debate about Temperature Sense, Muscle temperature perception make up a large part of Sense, the sense of pressure, etc. However, his work a result of the great interest triggered unlike his predecessors, he was not satisfied with by Goldscheiders exploration of the warm and a simple criticism of the different sub-senses but, cold points of the human skin.
With experiments instead, he pursued the intention of creating on himself and others he studied various human an encompassing generic term which included mucosa throat, nasal septum, stomach, etc. Dessoir The, sometimes very painful, experiments were realised that despite the rich findings and ambi- conducted only on himself and he even tested tious activities of his times, such an academic whether an exposed dental nerve triggered not teaching of the sense of touch appeared to be only pressure but also temperature sensations.
In light of this he stated, In such a way he also tested whether the end If the clarity of the presented circumstances is to head of a mans penis is sensitive to tempera- be improved by a precise method of description, ture. Experiments which he could not conduct the introduction of several new expressions is not on volunteers or, as was standard at his time, to be avoided .
Alluding to the terms optic and acoustic, He precisely described the test procedures and Dessoir suggested that the teaching of the sense the observed behavioural reactions of his test of touch therefore be called haptic. This word animals. Dessoir called the allowed itself a critical relationship to existing first two aspects of the sense of touch contact knowledge. In doing so, Dessoir, without explic- cold receptors in the skin as a result of a lack itly stating so, separates the perception of touch of anatomical-histological findings regarding the from the perceiving subjects point of view into matter.
The actively explor- After publishing his professorial dissertation, ing subjects perception of touch which result Dessoir turned to other areas of psychology and, from tactile and muscular sensations are, in his particularly, aesthetics and philosophy. Among opinion, independent phenomena Pselaphesie , others he wrote a comprehensive work about the which should be considered separately from the history of psychology  as an expansion and contact sense also on the conceptual level.
The re-working of his philosophical dissertation. This necessity of this terminological determination book is, even today, considered authoritative for was to be recognised only years later. Even if the history of 18th century psychology. He studied and received his post doctorate degree in law in Budapest and then he joined Georg Elias Mller in Gttingen, Germany to work in the field of experimental psychology.
Rvsz taught psychology in Budapest and emigrated to The Netherlands in or, according to some accounts, in He became a professor at the University of Amsterdam in and published, for the most part, in German and in the German language publications and was named an honor- ary member of the Deutschen Gesellschaft fr Psychologie German Society for Psychology.
Gza Rvsz left many and various marks with- in psychology. His comprehensive work includes numerous articles about music psychology [17, 18], the psychology of language , aptitude  and thought and he is considered the father of psychology for the blind. Besides music and language psychology, cal presentations with profound philosophical Rvsz also intensively studied and researched and epistemic arguments.
He intensively devoted the human sense of touch. In he published himself to the Kant thesis that all people even a two volume work with the title Die Formenwelt those born blind are equipped a priori with a des Tastsinnes Grundlegung der Haptik und der spatial perception. The psychological and physi- Blindenpsychologie  Fundamentals of Haptic ological experts of his time doubted the ability and the Psychology of the Blind. This posi- the findings of his time into the closed concept tion seemed to be supported by operations per- of haptic perception.
In doing so he supports his formed on people born blind which were unable perceptual-psychological work with experimen- to detect determine object or spatial informa- tal and observational studies, especially ones in tion. However, Rvsz was methodically brilliant which he conducted with patients who had been and proved with his analysis that the findings born blind and ones which had become blind from those born blind speak for the acceptance later in life.
Noticeably, and in contrast to his psy- of a haptic spatial perception which exists com- cho-physiological colleagues, he combines clini- pletely independently of visual perception. He decidedly refers to the visual this regard. In opposition to the dominant thesis influences which haptic perception is subject of the time from Gelb and Goldstein, , to in seeing people. In contrast, haptic percep- which stated that spatial perception is only pos- tion in those born blind can be considered sible with the help of the visual sense, Rvsz uninfluenced by visual experience and, there- proved that haptic illusions appear in the same fore, autonomous.
According to Rvsz, the fashion regardless of whether the subject is blind principles which underlie both forms of haptic or not. For Rvsz, these findings are a clear could only be explained when comparative stud- indication of the fact that the optical theory of ies were carried out on people with the visual visual perception is invalid. In fact, he insisted sense and on people who had been born blind. He does not only criticise independently from one another. Rvsz poses the numerous deficits in his colleagues working the question of whether haptic and visual per- methods but, rather, emphatically insisted that ceptions underlie the same or completely inde- haptic research must get away from the para- pendent organisational principles.
Supported by digms of optics. This made Rvsz, without tioned, oriented on visual perception. Under these a doubt, one of the most radical and decisive circumstances, haptic could not emancipate itself representatives of experimental touch research from optic. As a result, the entire research has in Germany.
With courage and entelechy, he not stagnated . He also argued that the phenom- only demanded an independent methodology for enological, descriptive approach within psychol- haptic research but, rather, postulated that the ogy can represent a research instrument which entire dimensions of human haptic be a totally is capable of producing statements about haptic separate field of research. In doing so he takes perception. Like David against the Platonian position in which vision Katz, he emphasises the essential importance of represents the dominant sense.
He doesnt doubt movements in the touch process. This process the importance of the sense of vision but doesnt itself is understood by Rvsz as a successive- agree with the general degradation of the sense analytical process with the goal of object recog- of touch as a lower sense. Rather, he showed, nition in opposition to visual perception to with his studies of the blind, which incredibly which he attributes a simultaneous, synthetic complex accomplishments the visually-indepen- process with the same goal.
Rvsz postulates another difference to visual As a result, the influence of Rvszs research perception in the so called stereo-plastic prin- of blindness on the conception of haptic is ciple which he himself refers to as the funda- undeniable. It is only logical that Rvsz, in his mental principle of haptic perception and which attempt to organise haptic perception, speaks is non-existent in visual discernment. As the psychology of gestalt is, how- ever, for the most part, limited to the areas of visual perception, Rvsz constantly attempted to define the particularities of haptic gestalt principles as compared to visual ones.
Rvsz  tions, developed successively. In order to test his views, he had subjects feel unknown bottle forms with both hands and interrupted the touch pro- tangible objects. The need to explore objects cess at various time intervals. He recorded the haptically is, according to Rvsz, an exploratory results of the active form recognition up to the principle which we can suppress only with effort.
With the help of It also leads us to collect information about co called photograms Rvsz analysed the work every perceivable characteristic within the realm movement of individual fingers during the scan- of haptic perception. He was unable to see a com- ning process. To do so, a light bulb was attached parable curiosity need to perceive in visual to the top of the middle finger. Photographic object exploration. The recorded light- cess as essential, and again, as a major difference point recordings allowed Rvsz to observe that, to visual perception. He differentiates between during the exploration process, certain aspects receptive passive, contemplative, without of a form corners and edges were explored the aim of recognition and intentional atti- longer and more frequently than other elements tudes haptic exploration with the explicit goal Fig.
With this and other studies using film of object recognition . Rvsz called the technology, Rvsz examined the successive results of a receptive haptic exploration process nature of haptic object exploration. At the same haptomorphe Gestalten and those of intentional time he observed various exploratory phases attitudes optomorphe Gestalten. Together with Gza Rvsz, he conducted perceptual and mem- ory experiments on chickens.
In he became a professor of psychology and education at the Institute for Psychology at the university in Ros- tock, Germany. Together with his wife Rosa Katz he worked on the issues of child psychology, the phenomena of hunger and appetite as well as the senses of touch and vibration. In he fled Nazi Germany, first going to England and then, in , to Stockholm where he became a professor for education and psy- chology and where he died in With this work he decid- Rvsz  edly challenged the miserable position of touch sense research within psychology at the time and also the treatment of this sensory system as of the objects design.
Rvsz posits a sym- a lower sense. In addition to this, Katz hoped metrical movement-gestalt in which we tend to that a higher regard for the sense of touch with- perceive asymmetrical objects as symmetrical. Furthermore, ability of seeing people and those born blind he pointed out that the prevailing positions in to haptically gauge an objects proportions and the cognitive sciences would alter greatly if the translate them into an active structuring process.
Katz was convinced studies is the realisation that haptic perception that a higher regard for the occurrences tak- is always accompanied by an optification and ing place in the sense of touch would result in that visual perception is accompanied by a hap- its showing a fundamental character in, and tification. This means that, according to Rvsz, practical uses for, the fields of psychology and the haptic exploration process in seeing people education.
That the hand takes an exceptional is accompanied by a tendency to create a visual position here as a special touch-sense organ imagination of the object being felt. In a parallel is, for Katz, as self-evident as the important con- fashion, visual perception is checked and veri- fied by haptic experience haptification.
In this 1 The work was translated into English in by L. He not only discussed findings and phenomenological descriptions of perceptions of the sense of touch, but also pos- sible capacities for memory and hallucinations. Katzs content and methodology are obvi- ously influenced by E.
Weber, even though he didnt work with the meticulous strictness nor did he wish to as a result of his more material and practical orientation that was pre- scribed and demanded by the physiological and psychophysiological predecessor and con- temporaries. He referred to various aspects of E.
Webers works with reverence and honest acknowledgement, but categorically criticised the strict psychophysiological elementary analy- ses of his predecessor and contemporaries. Katz considered the separate analysis of individual stimuli and singular phenomena in an artificial laboratory environment to be atomism and he didnt believe that it could lead to a compre- hensive understanding of the human sense of touch. Katz stressed that the sensory-physiologi- cal approach to sensory research often merely examined artificial products and rarely the real FIGURE 8.
Katz acknowledged the basic successes of sensory-physiology but, for the sense of touch, this fragmentation of the nection between hand activities and brain mat- realm of ones sensory experience was an unac- uration already recognised in developmental ceptable methodology. He commented ironically psychological circles. Katz looked into all of the on the single-stimuli studies of his colleagues: important findings from research into the sense Most people will probably die without ever having of touch which were available at the time. In as experienced the irritation of an isolated pressure much, his work from is not only a collection or warmth point.
The same can be said about a of the arguments based on his own studies but, real spatial threshold . This a psychological perspective. Hence, it becomes method contains measured values as well as dif- understandable that Katz deals with the physi- ferentiated verbal judgements of the test persons ological basics or the anatomical discussions these described aspects of his touch-sense very superficially if at all.
Cognitive and Tactile Factors Affecting Human Haptic Performance in Later Life
Influenced by Gestalt research taking on a considerable importance. He was of object and surface properties can only be much more interested in redefining the position determined when the subject actively moves his of the sense of touch within the hierarchy of the exploratory extremities over the object structure senses and within psychology. As a result, his in question. In order to examine this central func- work contains manifold and diverse refer- tion in an experimental situation, Katz chose a ences to relationships between the various sens- paradigm supported by the recognition the sur- es.
With comparisons and analogies of broad and face qualities of various paper types. In one such specific quality, he draws connections between experiment he had subjects compare two sheets the sensory modalities and refers, whenever pos- of paper chosen from a selection of 14 industri- sible, to the exceptional qualities of the possible ally prepared paper types and then order them in touch processes.
Katz was not afraid of a direct, an attempt to judge the test persons differentia- but well thought out, comparison of the sense tion thresholds. Katz is aware of the fact that the of touch and its specific capabilities with those test persons tendency to unsystematically order of the other senses.
That significant differences the paper according to roughness represented between vision and touch become apparent was a methodological problem. Katz used this test made very clear by Katz especially with the arrangement with variations as a basis for help of examples regarding the ability to differen- several different experiments into different ques- tiate between various surface properties. He, for example, reduced the size of the His dealings with the research methods of his stimuli paper pieces to 2 mm in diameter and, day and those of his predecessors led Katz to the in turn, determined the differentiation thresh- opinion that, until then, very little or no attention olds regarding the provided papers.
In other had been paid to movement as a formative force experiments, he limited the subjects ability to of the sense of touch . He complained that the move their fingers sideways while exploring atomistic methodology of sensory-physiology the papers surface and observed that the test which was significantly influenced by research persons differentiation abilities were almost into the optical system had blocked the sci- completely forfeited.
He came to the same con- entists view of the exploratory movements of clusion when the papers surface was presented the touching test person despite the fact that, to a finger at rest passive. He varied the experi- according to Katz, the actual performance of the ments by isolating the subjects finger tips with human sense of touch is considerably determined different materials e.
To his sur- cesses coming about at all. Again, Katz referred prise, the test persons were very well able to dif- to E. Weber here and, in order to caricaturise ferentiate between the various types of paper. He the one-dimensional research approaches of his also gave his subjects the task of differentiating contemporaries, he resorted to biting analogies between these papers by means of feeling them which several of his colleagues surely did not with a wooden peg.
Again, they were capable of find humorous: Examining the sense of touch in differentiating between them. Katz recognised a state of rest is almost like wanting to investigate that vibrations which appear during the touch the musculature of the legs after having put them process represent the crucial factor in stimulus in a plaster cast . He eliminated the influence acoustic For Katz, the central importance of the move- information, as far as possible, by closing the ments for the performance of the sense of touch auditory canal of his subjects during the touch is mainly a result of observations made while process.
Like E. Weber before him, he the subjects finger tips in these experiments. The paper samples were attached to a rotating disk. With the adjust- able motor it was possible to achieve constant, steady speeds Katz . He nullified. All paper types appeared to be equally also attempted to determine which factors and smooth. These, and other, studies led Katz to the measures were capable of impeding the percep- conclusion that the vibrations which accompany tion process. To this purpose, the fingertips the touch process are crucial to the perceptual were rubbed extensively with a Turkish towel or results when assessing object surfaces.
With this methodology With a similarly elaborate apparatus Katz in mind, it comes as no surprise that Katz also examined the questions of how quickly test included amputees in his experiments. He had 19 subjects were able to correctly identify different forearm amputees and 16 above-elbow amputees types of paper and of which influence the number feel various materials e. The recognition times cloth with the stump of their amputated limbs with the use of one finger were ca. Both groups showed substantial faster. Katz explained the superiority of using five recognition capabilities on average, nine of 12 fingers with reference to Helmholtz  and the materials were correctly identified.
Katz observed maximum distinguishabil- ous trials and experiments. At this speed, a stimulation stressed that they are apparently never in a time of 1. This phenomenological approach out. This cord is then attached tinuously but, rather, with interruptions. In Alongside this explicit stressing of the move- this way, exploratory movements of the finger ments in active touching processes, the impor- were depicted and plotted on a curve Figs tance of the fact that he dedicated himself to the 10 and With quite a low number of test experimental analysis of the exploratory move- subjects, and the resulting uncertainty in the ments must be recognised even if he did so quality of the data, Katz ascertained that finger with simple methods.
His work marked the begin- movements towards the body were made more ning of a search for answers to these questions quickly than corresponding movements made in within haptic questions which are, even today, the direction away from the body. Additionally, extremely important and methodically difficult he states that the movements made towards the to research. He also observed the fact that temperature Katz was very well aware of the methodologi- perception plays an important part in the judge- cal limitations of his trials but he stressed the ment of materials and surface qualities.
Katz sys- necessity and legitimacy of such pilot studies. He then compared examine the movements of the finger in its the relationships of these judgements to the natural dressing. This is a goal which is to be specific thermal conduction coefficients of each admired especially when one considers the material. Cognitive aging manifests as a mild age-related decline in cognitive functions with highly individual changes in general cognitive capacity, as well as domain-specific declines in fluid reasoning, mental processing speed, episodic memory, and spatial ability  — .
The mechanisms that are thought to underlie these decreases fall into 2 general categories . On the one hand, one global undifferentiated mechanism, such as cognitive processing-speed, could account for the loss of performance . On the other hand, the age-related decline might be caused by specific cognitive mechanisms, such as executive functioning, which is used in service of many cognitive tasks, occurring in everyday life or work related tasks .
The majority of investigations into age-related decline of sensory, sensorimotor, and cognitive functions have looked at the components individually, but it is generally accepted that the loss of functional integrity between the domains is functionally coupled  , . In recent years, a number of studies have reported an increase in co-variation or interdependence between sensory and cognitive functions in old age  ,  ,  ,  , . Data from large-scale cross-sectional and longitudinal studies such as the Berlin aging study BASE,  showed strong relationships between intellectual and sensory functioning in old age .
Experimental studies investigating the relationship between sensory functions and cognition used either a simulated loss of sensation to explore the effects on cognitive function  —  , or cognitive load manipulations on sensorimotor performance  , . In general, both interventions affected older adults' performance more than that of younger adults. Some authors hypothesized that sensory and sensorimotor declines may precede and predict cognitive decline  ,  , whereas others refrained from assigning priority to any of the 3 domains, but favored either a common cause affecting all functions  , an increase in cross-domain resource competition, or a combination of both .
Particularly in old age, sensory, sensorimotor, and cognitive performance determines the extent to which a mobile and independent life is possible . For this reason, the investigation of the development of these processes into late adulthood is not only of general interest, but offers a direct link to gerontological practice  , .
In the present study, we investigated the extent to which the age-related decline in haptic performance is related to the individual loss of tactile acuity and cognitive capacity.
Individual haptic performance i. Trend lines are inserted for male solid blue , female solid red , and all subjects dashed black. Group data for haptic performance i. Black bars indicate SEM. Individual two-point discrimination thresholds i. Group data for tactile performance i. Individual cognitive performance scores assessed with the RSPM test i. Trend lines are shown for male solid blue , female solid red , and all subjects dashed black.
Second order partial correlations controlling for the age of subjects were used to investigate the relationships between tactile, haptic, and cognitive performance. Second order partial correlations controlling for the age of all subjects were calculated. It has been known for some time that human haptic performance decreases as a function of age  , but less is known about the neural mechanisms underlying these changes.
In a study about haptic performance of adults under conditions were finger movements were restricted, or subjects had to wear gloves, the speed of object identification was more affected than accuracy of identification . In contrast, we have shown recently that the aging process affects both, the speed and the accuracy of haptic identification of unfamiliar objects  ,  cf. In the present study, we investigated age-related changes in haptic performance by combining a haptic task with tests of tactile acuity and of cognitive performance, as the latter abilities are crucial prerequisites for haptic object exploration.
Confirming previous findings  ,  ,  , we found a significant age-related decline in both tactile and haptic performance. Furthermore, the RSPM test confirmed common knowledge of an age-related decline in cognitive abilities in old age  , . Correlational analyses revealed a strong relationship between individual cognitive and haptic performance, but only relatively minor relationships between individual tactile and haptic performance, as in the present study only data from male subjects reached significance criteria.
In female subjects, who generally showed a stronger decline in haptic and cognitive performance, no relationship between tactile acuity and haptic performance was found. Our results indicate that the well-documented loss of tactile acuity in old age  ,  ,  ,  ,  ,  ,  ,  —  might not be the primary cause of the age-related decline in haptic performance in later life. Instead, intellectual functioning seems to be more predictive than the sensory measure.
This finding has strong implications for the view that aging is associated with greater correlations between intellectual status and sensorimotor performance  , . From previous work in older adults, we know that human tactile, haptic, and fine-motor performance decreases as a function of age, but can be restored to some extent by physical intervention programs  ,  , or by focused peripheral stimulation paradigms  ,  ,  , .
Under such conditions, the stimulation-based improvement of tactile acuity was shown to support exploratory procedures in haptic object exploration and object manipulation in fine-motor tests  , . From experiments in healthy adults  older adults  and patients suffering from impaired tactile perception following central  or peripheral neurological disorders  , it is known that tactile acuity is indispensable for object manipulation, as well as for object recognition.
Dellon and Kallman  investigated functional sensation in the hands of patients with functional limitations of the median nerve, and found that the moving two-point discrimination test best correlated with the patients' ability to identify objects using their fingertips. Furthermore, the time required for object recognition correlated best with the static two-point discrimination test . From our own experiments, we know that the two-point discrimination paradigm provides very accurate and reliable data for performance on stimuli discrimination tasks  ,  ,  —  ,  ,  , .
In a recent study, Legge and coworkers investigated tactile acuity over the entire human lifespan in sighted and blind individuals by means of newly designed tactile-acuity charts that require active exploration . The authors demonstrated good quantitative agreement between their data acquired in sighted subjects and the data of other studies, thereby providing a degree of validity for their measurement technique.
Further experiments are required to investigate the relationship between data acquired by common measures of tactile acuity i. While our results revealed a poor haptic performance of female subjects as compared to male subjects, other studies reported that woman at all age consistently outperformed men in fine dexterity tasks  , . Kleinman and colleagues, who performed an early investigation into haptic exploration performance in young, middle-aged, and elderly adults, reasoned that the documented loss of performance in old age is due to less logical, systematic, and detailed exploratory procedures that were applied by elderly subjects .
As such, older subjects, when asked to identify geometric objects in a purely haptic experiment, seemed to use inappropriate exploratory procedures, which harmed their object recognition. This finding was supported by self-reports from a number of female subjects in the present study, who indicated that they were hardly able to match the haptic impression with the respective visual perception, because they did not know which exploratory procedure to apply. Although all subjects were informed about object-related structural cues e.
Male subjects, even those who showed relatively poor haptic performance, did not indicate any problems with handling of the objects. Our findings are in line with neuropsychological research on visuospatial tasks, particularly those that require mental rotation of objects, as extremely consistent gender differences have been found in these studies  , .
Mental rotation involves the active manipulation of objects in the mind, a process that is based on visuo-spatial memory functions  , i. Several studies have found males to perform better than females in mental rotation tasks  ,  although it remains unclear which specific biological or environmental factors cause women's poorer performance on such tasks . The demonstrated significant correlation between haptic performance and general intelligence, as assessed by the RSPM test, is also supported by a positive correlation between visuospatial and mathematical abilities with respect to gender differences  , .
Besides evolutionary and hormonal mechanisms contributing to the reported robust gender-specific differences, one has also to consider the effects of gender role socialization on spatial ability . From our experiment, we conclude that comprehension of the geometric structure of an object is the first requirement for haptic exploration. This process seems to be a demanding intellectual task in old age, with subjects with high RSPM-scores faring the best.
Specifically, it is necessary to comprehend the global geometric structure of the visually presented sample objects, as well as the structure of the haptically explored object. Mental rotation skills are required throughout the process, as the subjects have to align the explored object in their hand relative to the visually presented objects. Once the alignment is completed, the tactile acuity of the fingertips, as assessed by the two-point discrimination test, seems to be the secondary requirement for successful execution of the task.
The subjects have to check for characteristic details of the explored object in their hand and assign it to one of the presented objects. This assumption is supported by data from the correlation analyses, where only the data from male subjects, who performed better on average, showed a significant relationship between tactile acuity and haptic performance. In female subjects, who seemed to have more problems with the comprehension of global object structure and the alignment of object orientation, tactile acuity seems to play a subordinate role.
It is an interesting remaining question in how far the observed gender differences in haptic identification of unfamiliar objects might to some extend be caused by the fact that we used arbitrary instead of familiar objects. It is conceivable that male subjects, who are typically more frequently exposed to manual tasks associated with manipulating tools or office objects either during work or free time, which might have translated into an advantage performing the haptic task.
In fact, it was shown recently that object familiarity modulates the relationship between visual object imagery and haptic shape perception . Accordingly, further studies are needed using familiar objects, although this poses problems because most familiar objects are heavily overlearned. Our findings are partially in line with the findings of Norman and colleagues, who compared pure haptic, pure visual and cross-modal object recognition in younger and older adults .
These observations were reproduced in a more recent work of the authors investigating age-related changes in the haptic perception of three-dimensional surface shape .
The absence of correlation between tactile acuity and haptic performance in these studies might be attributable in part to the objects used, that were larger than the objects used in our current experiment. Furthermore, it is possible that proprioceptive functions contribute to the haptic exploration of larger objects e. Using a proprioceptive hand function test recently developed by our group to be published , we found that proprioceptive functions of the human hand are subject to only minimal age-related changes as compared to the dramatic changes in tactile acuity  ,  ,  ,  ,  ,  — .
The unfamiliar, cubic objects used in our study require tactile acuity to perceive the different surface textures of the upper and lower sides see methods section , and to align the object in the hand accordingly for exploration. Furthermore, some constructional differences between the 5 classes of objects used are based on tiny details in the lower centimeter-range, which require at least basic tactile acuity. The results reported herein support recent findings of a sensory-cognitive link found in the auditory, visual, and tactile domains in healthy aging adults  ,  , .
In the above-mentioned domains, basic measures of absolute sensory thresholds, such as pressure threshold sensitivity, hardly rely on cognitive resources. We have demonstrated that the age-related decline of cross-modal haptic performance, which occurs in late adulthood, is primarily related to cognitive functioning, rather than to tactile acuity.
Tactile acuity seems to be a predictor of haptic performance, but only if the cognitively demanding first phase is completed successfully. We tested 81 right handed volunteers aged 45 to 94 years 32 males, mean age In all subjects, the educational level number of school years and training was balanced males All subjects were neurologically healthy, as assessed by a neurologist.
Original Research ARTICLE
Individuals with polyneuropathy, peripheral nerve lesions, carpal tunnel syndrome, or other neurological disorders were excluded from the study. Eligibility criteria were lucidity, independence in activities of daily living, absence of motor handicaps such as functional impairments due to arthritis, or other causes of joint immobility. Furthermore, medication with central nervous effects in subjects' present or recent reported history past 5 years was a criterion for exclusion.
Tactile sensitivity of the subjects' hands was checked prior to the experiments as a check for peripheral neuropathies . Subjects with a score lower than 28 points were excluded. This study was approved by the Ethics Committee of the Ruhr-University of Bochum, and all subjects provided written informed consent before participating. The use of unfamiliar, instead of common objects, prevents the influence of prior knowledge of structural information, and creates a comparable initial test-situation for all subjects. Each object was constructed as a cuboid 1. These constructional differences were highlighted in terms of color.
All objects had a smooth surface structure on the sides, a plain bottom side, and a nubby upper side that could be used as tactile cue for orientation during haptic exploration fig. To prevent the objects from falling apart, all components were glued together. One sample of each set was placed on a desk in front of the subject.
The viewing conditions were full-cue, and the objects were binocularly viewed by observers under ample lighting . In a familiarization phase, individual haptic and visual exploration of the objects was allowed. For this aim, participants were asked to hold the sac with their left hand underneath the desk, while explorative movements were exclusively performed with the right hand. Each object had to be allocated to one of the visible samples on the desk, by removing it from the sac and placing it in a container behind the specific sample.
No visual verification was permitted.click here
Human Haptic Perception: Basics and Applications
The subject was instructed to perform as quickly and as accurately as possible time limit of 4 minutes per session; remaining objects were considered to be errors. After a familiarization training 3 consecutive sessions , all subjects indicated good comprehension of the test. The estimation of individual performance was done by counting the number of errors occurring in the fourth test session. In each group, the objects consisted of a cuboid 1. Spatial two-point discrimination thresholds were assessed on the tips of all fingers of the right hand using the method of constant stimuli as described previously  ,  ,  ,  ,  , .
We tested 7 pairs of brass needles; in addition, zero distance was tested with a single needle. To overcome problems in the use of two-point measurements associated with hand-held probes, we used a specifically designed apparatus that secures a standardized form of testing see figures in  , . The apparatus allowed rapid switching between pairs of needles featuring different separations or 1 single needle control condition.
All tactile stimuli were applied to a fixed position on the skin of the fingertips for approximately 1 s. To account for the age-related decline in tactile acuity  ,  ,  ,  ,  , we used different settings of the two-point discrimination set-up for subjects below 60 years of age 1. The diameter of the needles was 0. Application force was approximately to mN. Fixation of the tested fingers prevented explorative finger movements. All 8 test conditions were presented 8 times in a randomized order, resulting in a total of 64 tests per session. The subjects, who were not informed of the ratio of needle-pairs to single needles i.
All subjects had to attend 2 training sessions to get used to the testing procedure before the assessment was started in the third session. All subjects who participated in the present study knew the two-point discrimination test from previous studies. Example of the typical two-point discrimination performance of an older adult. Correct responses in percentages blue squares are plotted as a function of needle distances.
Based on these results, a logistic regression is calculated red squares. Compared to other tests, RSPM scores are recognized as reliable estimates of general intelligence Spearman's g factor . We applied the paper-and-pencil version of the RSPM to the subjects. The 5 sets A, B, C, D, and E of tasks are arranged according to the principles of increasing complexity . In each task, a specific pattern or a number of geometrical structures are presented, with 1 part of the pattern or 1 component of the structures missing. On the basis of 6—8 presented solutions the subject has to decide which one is appropriate to complete the given pattern or set of structures.
ANOVAs were calculated based on subsamples of the population. Competing Interests: The authors have declared that no competing interests exist. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. National Center for Biotechnology Information , U. PLoS One. Published online Jan Dinse 2. Hubert R. Daniel Goldreich, Editor. Author information Article notes Copyright and License information Disclaimer.
Received Sep 19; Accepted Dec Copyright Kalisch et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. This article has been cited by other articles in PMC. Abstract Background Vision and haptics are the key modalities by which humans perceive objects and interact with their environment in a target-oriented manner.
Conclusions Haptic object recognition is a demanding task in old age, especially when it comes to the exploration of complex, unfamiliar objects. Age-related factors contributing to the loss of tactile acuity and cognition Physiological brain aging is characterized by a number of alterations that provoke age-dependent decline of sensory processing, motor performance, and cognitive function  — . Interdependence between sensorimotor functioning and cognition in later life The majority of investigations into age-related decline of sensory, sensorimotor, and cognitive functions have looked at the components individually, but it is generally accepted that the loss of functional integrity between the domains is functionally coupled  , .
Open in a separate window. Figure 1. Development of haptic performance in later life. Figure 2. Development of tactile performance in later life. Figure 3. Development of cognitive performance in later life. Correlation of haptic, tactile, and cognitive performance Second order partial correlations controlling for the age of subjects were used to investigate the relationships between tactile, haptic, and cognitive performance.
Figure 4. Correlation of haptic, tactile, and cognitive performance. Discussion It has been known for some time that human haptic performance decreases as a function of age  , but less is known about the neural mechanisms underlying these changes. Tactile acuity as a prerequisite for haptics From previous work in older adults, we know that human tactile, haptic, and fine-motor performance decreases as a function of age, but can be restored to some extent by physical intervention programs  ,  , or by focused peripheral stimulation paradigms  ,  ,  , .
Gender-specific differences in haptic performance While our results revealed a poor haptic performance of female subjects as compared to male subjects, other studies reported that woman at all age consistently outperformed men in fine dexterity tasks  , . Sensory-cognitive link in later life The results reported herein support recent findings of a sensory-cognitive link found in the auditory, visual, and tactile domains in healthy aging adults  ,  , .
Conclusion We have demonstrated that the age-related decline of cross-modal haptic performance, which occurs in late adulthood, is primarily related to cognitive functioning, rather than to tactile acuity. Materials and Methods Subjects We tested 81 right handed volunteers aged 45 to 94 years 32 males, mean age Figure 5. Objects used for the haptic object recognition test. Two-point discrimination test Spatial two-point discrimination thresholds were assessed on the tips of all fingers of the right hand using the method of constant stimuli as described previously  ,  ,  ,  ,  , .
Figure 6. Psychometric function for two-point discrimination performance. Footnotes Competing Interests: The authors have declared that no competing interests exist. References 1. Percept Psychophys. Haptic perception: a tutorial. Atten Percept Psychophys. Hsiao SS, Yau J. Neural basis of haptic perception.
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