Tactual perception: a review of experimental variables and procedures

This paper reviews the literature on tactual perception. Throughout this review, we will highlight some of the most relevant aspects in the touch literature: type of stimuli; type of participants; type of tactile exploration; and finally, the interaction between touch and other senses. Regarding type of stimuli, we will analyse studies with abstract stimuli such as vibrations, with two- and three-dimensional stimuli, and also concrete stimuli, considering the relation between familiar and unfamiliar stimuli and the haptic perception of faces. Under the "type of participants" topic, we separated studies with blind participants, studies with children and adults, and also performed an overview of sex differences in performance. The type of tactile exploration is explored considering conditions of active and passive touch, the relevance of movement in touch and the relation between haptic exploration and time. Finally, interactions between touch and vision, touch and smell and touch and taste are explored in the last topic. The review ends with an overall conclusion on the state of the art for the tactual perception literature. With this work, we intend to present an organised overview of the main variables in touch experiments, compiling aspects reported in the tactual literature, and attempting to provide both a summary of previous findings, and a guide to the design of future works on tactual perception and memory, through a presentation of implications from previous studies.     

The First Sense: A Philosophical Study of the Sense of Touch

In this essay, I review Matthew Fulkerson's The First Sense: A Philosophical Study of the Sense of Touch. In this first philosophical book on the sense of touch, Fulkerson provides an account of the nature and content of tactual experience. Central to Fulkerson's view is the claim that exploratory action plays a fundamental role in touch. In this review, I put pressure on two of his arguments: (1) the argument that tactual experience is unisensory and (2) the argument that tactual experience does not depend on explicit bodily awareness.     

Similarity of tactual and visual picture recognition with limited field of view.

Subjects attempted to recognize simple line drawings of common objects using either touch or vision. In the touch condition, subjects explored raised line drawings using the distal pad of the index finger or the distal pads both of the index and of the middle fingers. In the visual condition, a computer-driven display was used to simulate tactual exploration. By moving an electronic pen over a digitizing tablet, the subject could explore a line drawing stored in memory; on the display screen a portion of the drawing appeared to move behind a stationary aperture, in concert with the movement of the pen. This aperture was varied in width, thus simulating the use of one or two fingers. In terms of average recognition accuracy and average response latency, recognition performance was virtually the same in the one-finger touch condition and the simulated one-finger vision condition. Visual recognition performance improved considerably when the visual field size was doubled (simulating two fingers), but tactual performance showed little improvement, suggesting that the effective tactual field of view for this task is approximately equal to one finger pad. This latter result agrees with other reports in the literature indicating that integration of two-dimensional pattern information extending over multiple fingers on the same hand is quite poor. The near equivalence of tactual picture perception and narrow-field vision suggests that the difficulties of tactual picture recognition must be largely due to the narrowness of the effective field of view.     

Tactual, visual, and cross-modal transfer of texture in 5- and 8-year-old children

Children's tactual, visual, and cross-modal transfer abilities for texture were investigated in a delayed matching-to-sample paradigm. Transfer performance from vision to touch was found to increase between 5 and 8 years of age, whereas transfer performance from touch to vision did not vary with age and matched touch-to-touch performance. Asymmetrical cross-modal abilities were observed at the age of 8 years, vision-to-touch transfer performance being higher than touch-to-vision transfer performance (experiment 2). This developmental pattern could not be attributed to limitations in the tactual or visual discriminability of the textures or to differences in tactual or visual memory between the two age groups (experiment 1). It is suggested that the increase with age in vision-to-touch performance may be related to the intervention of more efficient top-down perceptual processes in the older children.     

Using vision and dynamic touch to perceive the affordances of tools

The information that people use to perceive whether a tool is suitable for a certain task depends on what is available at a given time. Visually scanning a tool and wielding it each provide information about the functional attributes of the tool. In experiment 1, we investigated the relative contributions of vision and dynamic touch to perceiving the suitability of various tools for various tasks. The results show that, when both vision and dynamic touch are available, the visual information dominates. When limited to dynamic touch, ratings of suitability are constrained by the inertial properties of the tool, and the inertial properties that are exploited depend on the task. In experiment 2, we asked whether the manner in which a tool is manipulated in exploration depends on the task for which it is being evaluated. The results suggest that tools are manipulated in ways that reflect intentions to perceive particular affordances. Exploratory movements sometimes mimic performatory movements.     

Tactual perception of embossed Morse code and braille: the alliance of vision and touch

In three experiments observers made visual matches to tangible embossed patterns. Stained glass was used to blur vision and thus allow the effect of visual guidance of tactual exploration on the accuracy of symbol recognition to be evaluated. Stained glass rendered the embossed code invisible, but allowed sight of the hand. In the first experiment subjects identified patterns made up of dots and dashes drawn from Morse code; in the second and third experiments they studied braille. The results show that subjects are more accurate in 'reading' tangible codes when provided with visual guidance. Performance was higher for braille than for Morse code. Vision aided touch through the provision of a frame of reference and through sight of scanning movements. Naive sighted observers were able to identify invisible braille dots by watching other individuals touch the symbols, suggesting the importance of vision of kinesthetic patterns.     

Touch,awareness of touch,and compliance with a request

In certain situations it has been shown that touch has a positive effect on the compliance with a request expressed by a stranger. However, the difference between the effect of touch on request compliance between people who had noticed and those who had not noticed this contact has never been taken into account. In this experiment a female confederate asked 227 women to answer a questionnaire. When asking for their collaboration the forearm was or was not touched for a brief period of 1 to 2 seconds. Analysis showed that touch was associated with significantly higher compliance to the request but no difference was found between subjects who had noticed the tactual contact and subjects who had not noticed.     

Infinite utility: Anonymity and person-centredness

This paper addresses the nature of touch or ‘tactual perception’. I argue that touch encompasses a wide range of perceptual achievements, that treating it as a number of separate senses will not work, and that the permissive conception we are left with is so permissive that it is unclear how touch might be distinguished from the other senses. I conclude that no criteria will succeed in individuating touch. Although I do not rule out the possibility that this also applies to other senses, I suggest that the heterogeneity of touch makes it both distinctive and particularly problematic.     

Hand-movement profiles in a tactual—tactual matching task: Effects of spatial factors and laterality

We examined the effect of spatial factors and hemispheric lateralization upon hand-scanning strategies in 14 right-handed men tested in a tactual—tactual matching task. The experiment involved comparisons (judgments of same or different) between two objects sequentially touched by the fingertips of the left or right hand. Stimuli were made of smoothly joined cubes whose junctions were not haptically discernible. Exploratory strategies were inferred from the durations and locations of hand contacts with any of the cubes composing the stimuli. Accuracy was greater when the same stimulus was touched twice by the same hand than when different hands were used to feel it. With regard to strategies, both hands touched the upper parts of the object longer than the lower parts. Subjects also inspected more portions of the objects ipsilateral to the hand used. Overall differences in time spent touching cubes were greater for the right hand than for the left hand, showing that touch times were less evenly distributed on object parts for the former than for the latter. In this study, the process of information gathering by touch appears to be determined by the intertwining integration of contextual factors (e.g., stimulus position in space), biomechanical constraints on hand movements, and such cognitive factors as hemispheric differences on the ability to encode spatial pattern information.     

Texture perception in sighted and blind observers

The purpose of the present study was to evaluate the utility of visual imagery for texture perception. In Experiment 1, sighted, early-blind, and late-blind observers made relative smoothness judgments of abrasive surfaces using active or passive tough. In Experiment 2, subjects compared vision and touch in the accuracy of smoothness detection, using a broad range of textures, including very fine surfaces. No differences appeared between the sighted and the blind, and it did not matter if touch were active or passive. Vision and touch showed similar performance with relatively coarse textures, but touch was superior to vision for much finer surface textures. The results were consistent with the notion that visual coding of tactual stimuli is not advantageous (or necessary) for texture perception, since touch may hold advantages for the detection of the smoothness of surfaces.     

Touch and vision in normal and Down's syndrome babies

Two experiments are reported with young Down's syndrome and normal children matched for mental age, sex, and social class. In one, Down's syndrome children performed at chance level on two tactual--visual cross-modal tasks, and only the oldest succeeded with one of two visual--visual within-modal tasks. The modal children performed at above chance level on the visual--visual tasks, and on the tactual--visual tasks the oldest succeeded on two and the youngest on one of the tasks. These results suggest that Down's syndrome children may have some sort of difficulty involving tactual perception. The second experiment examined the effect of touch on visual behaviour. Down's syndrome children and their matched controls looked at pairs of shapes which sometimes could be touched and sometimes could not. In the former condition the Down's syndrome children touched less, and looking and touching was less coordinated than that of normal children. However, both groups made fewer but longer looks when they could touch the shapes. In the light of these results the role of tactual perception in Down's syndrome children is discussed.     

Person perception through facial photographs: Effects of glasses,hair, and beard on judgments of occupation and personal qualities

Thirty-two photographs of male faces, four for each combination of the presence and absence of glasses, hair, and beard, were rated by 75 judges on 23 scales, assessing the typicality for 15 occupations as well as eight personal qualities. The effects of facial attributes on ratings formed characteristic profiles for the different scales. The pattern of correlations between facial attributes and factor scores from a factor analysis of the ratings indicates that the judges associated wearing glasses with intellectualism and goodness, being bald with idealism, and wearing a beard with unconventionality and goodness. In two further experiments, judges were to identify each of three faces with one of three or four occupations; the results confirmed the operativeness of the profiles from the rating experiment.     

Perception of texture by vision and touch: multidimensionality and intersensory integration

A series of six experiments offers converging evidence that there is no fixed dominance hierarchy for the perception of textured patterns, and in doing so, highlights the importance of recognizing the multidimensionality of texture perception. The relative bias between vision and touch was reversed or considerably altered using both discrepancy and nondiscrepancy paradigms. This shift was achieved merely by directing observers to judge different dimensions of the same textured surface. Experiments 1, 4, and 5 showed relatively strong emphasis on visual as opposed to tactual cues regarding the spatial density of raised dot patterns. In contrast, Experiments 2, 3, and 6 demonstrated considerably greater emphasis on the tactual as opposed to visual cues when observers were instructed to judge the roughness of the same surfaces. The results of the experiments were discussed in terms of a modality appropriateness interpretation of intersensory bias. A weighted averaging model appeared to describe the nature of the intersensory integration process for both spatial density and roughness perception.     

VISUAL AND TACTUAL EXPLORATION IN RATS REARED IN DIFFERENT DEGREES OF VISUAL AND TACTUAL STIMULATION

NIELSEN, T. C. Visual and tactual exploration in rats reared in different degrees of visual and tactual stimulation. Scand. J. Psychol. , 1971, 12, 53–61. – Four groups of eight rats each were reared in the four possible combinations of high and low visual and high and low tactual stimulation. Early tactual enrichment increased later tactual exploration regardless of visual stimulation. Visual enrichment did not influence exploration in the tactual enrichment groups, but in the tactual deprivation groups it seemed to produce more visual and less tactual exploration. The most deprived group exhibited a high locomotor activity which could not be explained in terms of an increased tendency to explore.     

Visual and tactual texture perception: Intersensory cooperation

In three experiments, subjects were required to make texture judgments about abrasive surfaces. Touch and vision provided comparable levels of performance when observers attempted to select the smoothest of three surfaces, but bimodal visual and tactual input led to greater accuracy. The superiority of bimodal perception was ascribed to visual guidance of tactual exploration. The elimination of visual texture cues did not impair bimodal performance if vision of hand movements were permitted. It is suggested that touch may preempt vision when both sources of texture information are simultaneously available. The results support the notion that perception is normally multimodal, since restriction of the observer to either sense in isolation produces lower levels of performance.     

Perceptual equivalence between visual and tactual pattern perception: An anchoring study

An anchoring design was used to investigate correspondence between visual and tactual scaling of complexity when two samples of random polygons served as stimulus forms. The results support the conclusion that within an adjustment for differential acuity between vision and active touch input is referred to a common perceptual mechanism.     

Effects of tactual and phonological similarity on the recall of Braille letters by blind children.

Forty-eight severly blind children, able to cope with set-sizes of two and three, four, five or six serial items were tested on probed recall of Braille letters they could either name or discriminate, when the letters were (1) dissimilar in tactual characteristics and name sounds, (2) similar in feel, but different in name sound, and (3) dissimilar in feel but similar in name sound. Results showed that tactual similarity produced recall decrements by subjects able to be tested under set-sizes of up to five items, while phonological similarity produced recall decrements by subjects testable under set-sizes of five and six items. It was argued that tactual information survives perception and affects recall, and that blind children can encode tactual inputs either tactually or verbally, but that this probably depends upon different processes.     

Symmetry in haptic and in visual shape perception

Four experiments tested the hypothesis that bilateral symmetry is an incidental encoding property in vision, but can also be elicited as an incidental effect in touch, provided that sufficient spatial reference information is available initially for haptic inputs to be organized spatially. Experiment 1 showed that symmetry facilitated processing in vision, even though the task required judgments of stimulus closure rather than the detection of symmetry. The same task and stimuli failed to show symmetry effects in tactual scanning by one finger (Experiment 2). Experiment 3 found facilitating effects for vertically symmetric open stimuli, although not for closed patterns, in two-forefinger exploration when the fore-fingers had previously been aligned to the body midaxis to provide body-centered spatial reference. The one-finger exploration condition again failed to show symmetry effects. Experiment 4 replicated the facilitating effects of symmetry for open symmetric shapes in tactual exploration by the two (previously aligned) forefingers. Closed shapes again showed no effect. Spatial-reference information, finger movements, and stimulus factors in shape perception by touch are discussed.     

Tactual picture recognition in congenitally blind and sighted children

Three experiments were carried out to investigate tactual processing of two-dimensional raised line drawings by blind and blindfolded sighted children. The results showed an unexpected but consistent pattern indicating that the introduction of ‘meaning’ facilitated the performance of the blindfolded sighted children but caused a relative decline in the performance of the congenitally blind. A general lack of evidence distinguishing between recognition of objects that had or had not been directly experienced through touch suggested that the internal spatial representations of objects depended not only on perceptual information but also on knowledge derived from other sources.