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.     

Partial perceptual equivalence between vision and touch for texture information

The present study examined the extent to which vision and touch are perceptually equivalent for texture information in adults. Using Garbin's method, we selected two sets of textures having high versus low cross-modal dissimilarity values between vision and touch (Experiment 1). The two sets of textures were then used as material in a cross-modal matching task (Experiment 2). Results showed that asymmetries occurred in the performances when the stimuli had high cross-modal dissimilarity values, but not when the stimuli had low cross-modal dissimilarity values. These results extend Garbin's findings on shape information to the texture domain and support the idea that partial perceptual equivalence exists between vision and touch.     

Evidence for the duplex theory of tactile texture perception

Three experiments are reported bearing on Katz's hypothesis that tactile texture perception is mediated by vibrational cues in the case of fine textures and by spatial cues in the case of coarse textures. Psychophysical responses when abrasive surfaces moved across the skin were compared with those obtained during static touch, which does not provide vibrational cues. Experiment 1 used two-interval forced-choice procedures to measure discrimination of surfaces. Fine surfaces that were readily discriminated when moved across the skin became indistinguishable in the absence of movement; coarse surfaces, however, were equally discriminable in moving and stationary conditions. This was shown not to result from any inherently greater difficulty of fine-texture discrimination. Experiments 2 and 3 used free magnitude estimation to obtain a more comprehensive picture of the effect of movement on texture (roughness) perception. Without movement, perception was seriously degraded (the psychophysical magnitude function was flattened) for textures with element sizes below 100 microns; above this point, however, the elimination of movement produced an overall decrease in roughness, but not in the slope of the magnitude function. Thus, two components of stimulation (presumably vibrational and spatial) contribute to texture perception, as Katz maintained; mechanisms for responding to the latter appear to be engaged at texture element sizes down to 100 microns, a surprisingly small value.     

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.     

Texture discrimination with and without abrupt texture gradients.

A common assumption is that effortless, visual texture discrimination relies on the detection of gradients between two textures. This assumption was assessed in two experiments with manipulations that smoothed (Experiment 1) or interrupted (Experiment 2) the gradient between textures comprising L- and X-type micropatterns. Compared to discrimination performance when there was an abrupt discontinuity between juxtaposed textures, performance declined moderately (about 10 percent) when the texture boundary was smoothed. In this case the two textures were asymmetrically discriminated but there was no interaction of this asymmetry with the abruptness of the texture gradient. Abrupt texture gradients, therefore, are not a necessary condition for the asymmetrical discrimination of two textures. A comparison of discrimination performance with juxtaposed textures--having an abrupt gradient--and discrimination performance when the textures were separated into distinct regions--by non-textured areas--yielded very similar results across several texture pairs. Taken together these results indicate that, in certain instances, texture discrimination may involve pattern classification-like processes that are operative in the absence of texture gradients.     

Spatial representation by blind and sighted children

Spatial representation by 72 blind and blindfolded sighted children between the ages of 6 and 11 was tested in two experiments by mental rotation of a raised line under conditions of clockwise varied directions.Experiment 1 showed that the two groups were well matched on tactual recognition and scored equally badly on matching displays to their own mentally rotated position.Experiment 2 found the sighted superior in recall tests. There was a highly significant interaction between sighted status and degree of rotation. Degree of rotation affected only the blind. Their scores were significantly lower for rotating to oblique and to the far orthogonal directions than to near orthogonal test positions. On near orthogonals the blind did not differ from the sighted.Age was a main effect, but it did not interact with any other variable. Older blind children whose visual experience dated from before the age of 6 were superior to congenitally blind subjects, but not differentially more so on oblique directions.The results were discussed in relation to hypotheses about the nature of spatial representation and strategies by children whose prior experience derived from vision or from touch and movement.     

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.     

Intersensory conflict between vision and touch: the response modality dominates when precise, attention-riveting judgments are required

In four experiments, reducing lenses were used to minify vision and generate intersensory size conflicts between vision and touch. Subjects made size judgments, using either visual matching or haptic matching. In visual matching, the subjects chose from a set of visible squares that progressively increased in size. In haptic matching, the subjects selected matches from an array of tangible wooden squares. In Experiment 1, it was found that neither sense dominated when subjects exposed to an intersensory discrepancy made their size estimates by using either visual matching or haptic matching. Size judgments were nearly indentical for conflict subjects making visual or haptic matches. Thus, matching modality did not matter in Experiment 1. In Experiment 2, it was found that subjects were influenced by the sight of their hands, which led to increases in the magnitude of their size judgments. Sight of the hands produced more accurate judgments, with subjects being better able to compensate for the illusory effects of the reducing lens. In two additional experiments, it was found that when more precise judgments were required and subjects had to generate their own size estimates, the response modality dominated. Thus, vision dominated in Experiment 3, where size judgments derived from viewing a metric ruler, whereas touch dominated in Experiment 4, where subjects made size estimates with a pincers posture of their hands. It is suggested that matching procedures are inadequate for assessing intersensory dominance relations. These results qualify the position (Hershberger & Misceo, 1996) that the modality of size estimates influences the resolution of intersensory conflicts. Only when required to self-generate more precise judgments did subjects rely on one sense, either vision or touch. Thus, task and attentional requirements influence dominance relations, and vision does not invariably prevail over touch.     

Early- and late-onset blindness both curb audiotactile integration on the parchment-skin illusion

It has been shown that congenital blindness can lead to anomalies in the integration of auditory and tactile information, at least under certain conditions. In the present study, we used the parchment-skin illusion, a robust illustration of sound-biased perception of touch based on changes in frequency, to investigate the specificities of audiotactile interactions in early- and late-onset blind individuals. Blind individuals in both groups did not experience any illusory change in tactile perception when the frequency of the auditory signal was modified, whereas sighted individuals consistently experienced the illusion. This demonstration that blind individuals had reduced susceptibility to an auditory-tactile illusion suggests either that vision is necessary for the establishment of audiotactile interactions or that auditory and tactile information can be processed more independently in blind individuals than in sighted individuals. In addition, the results obtained in late-onset blind participants suggest that visual input may play a role in the maintenance of audiotactile integration.     

Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem concerning tactile pictorial perception by the blind. The aim of the experiments reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute values of 3-D properties from 2-D patterns read by the finger pads, the abilities of participants to perceive gradients lying between known maxima and minima were assessed. Experiment 1 involved blindfolded sighted participants making verbal magnitude estimations of texture-gradient magnitudes corresponding to plane surfaces at different slants. In experiment 2 the participants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind participants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for learning. Texture gradients appear as informative to the blind as they do to the sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigated.     

Imposed vibration influences perceived tactile smoothness

According to the duplex theory of tactile texture perception, detection of cutaneous vibrations produced when the exploring finger moves across a surface contributes importantly to the perception of fine textures. If this is true, a vibrating surface should feel different from a stationary one. To test this prediction, experiments were conducted in which subjects examined two identical surfaces, one of which was surreptitiously made to vibrate, and judged which of the two was smoother. In experiment 1, the vibrating surface was less and less often judged smoother as the amplitude of (150 Hz) vibration increased. The effect was comparable in subjects who realized the surface was vibrating and those who did not. Experiment 2 showed that different frequencies (150-400 Hz) were equally effective in eliciting the effect when equated in sensation level (dB SL). The results suggest that vibrotaction contributes to texture perception, and that, at least within the Pacinian channel, it does so by means of an intensity code.     

Retention of high tactile acuity throughout the life span in blindness

Previous studies of tactile acuity on the fingertip, using passive touch, have demonstrated an age-related decline in spatial resolution for both sighted and blind subjects. We have reexamined this age dependence with two newly designed tactile-acuity charts that require active exploration of the test symbols. One chart used dot patterns similar to braille, and the other used embossed Landolt rings. Groups of blind braille readers and sighted subjects ranging from 12 to 85 years old were tested in two experiments. We replicated previous findings for sighted subjects by showing an age-related decrease in tactile acuity by nearly 1% per year. Surprisingly, the blind subjects retained high acuity into old age, showing no age-related decline. For the blind subjects, tactile acuity did not correlate with braille reading speed, the amount of daily reading, or the age at which braille was learned. We conclude that when measured with active touch, blind subjects retain high tactile acuity into old age, unlike their aging sighted peers. We propose that blind people's use of active touch in daily activities, not specifically braille reading, results in preservation of tactile acuity across the life span.     

Visual discrimination of local surface depth and orientation

Many theoretical analyses of 3-dimensional form perception assume that visible surfaces in the environment are perceptually represented in terms of local mappings of metric depth and/or orientation. Although this approach is often taken for granted in the study of human vision, there have been relatively few attempts to demonstrate its psychological validity empirically. In an effort to shed new light on this issue, our research has been designed to investigate the accuracy with which observers can discriminate metric depth and orientation intervals on smoothly curved surfaces. Observers were presented with visual images of surfaces defined by shading and/or texture, on which two pairs of points were designated with small dots. In Experiment 1, their task was to identify which pair of points had a greater difference in depth; in Experiment 2 they were required to judge which pair had a greater difference in orientation. The Weber fractions obtained for these tasks were 10 to 100 times greater than those that have been reported for other types of sensory discrimination, indicating that the perception of metric structure from these displays is surprisingly coarse grained.     

Perception of Size of Movement Patterns

Physiological data suggest that perception and memory of kinesthesis may differ depending on whether a movement pattern is actively commanded or passively induced. An attempt was made to demonstrate a difference between these two types of movements by employing a cross-modal visual recognition test of size perception. Absolute and algebraic errors in the matching of kinesthesis with vision were measured. Positive algebraic errors were seen indicating that subjects’ perception for the size of kinesthetic movement patterns was magnified as compared to vision. Active kinesthesis was matched with vision more accurately than was passive kinesthesis, and the data yielded information about the differential contribution of active and passive muscle compartments to the global kinesthetic perception of voluntary movement. Cross-modal matching of kinesthesis with vision was in certain cases as accurate as visual intramodal matching. It was argued that active kinesthesis has internal references, and vision has external references to facilitate the similar-size recognition performance.     

Multisensory integration of vision and touch in nonspatial feature discrimination tasks

Multisensory integration of nonspatial features between vision and touch was investigated by examining the effects of redundant signals of visual and tactile inputs. In the present experiments, visual letter stimuli and/or tactile letter stimuli were presented, which participants were asked to identify as quickly as possible. The results of Experiment 1 demonstrated faster reaction times for bimodal stimuli than for unimodal stimuli (the redundant signals effect (RSE)). The RSE was due to coactivation of figural representations from the visual and tactile modalities. This coactivation did not occur for a simple stimulus detection task (Experiment 2) or for bimodal stimuli with the same semantic information but different physical stimulus features (Experiment 3). The findings suggest that the integration process might occur at a relatively early stage of object-identification prior to the decision level.     

Reduced visual acuity is mirrored in low vision imagery

Research has examined the nature of visual imagery in normally sighted and blind subjects, but not in those with low vision. Findings with normally sighted subjects suggest that imagery involves primary visual areas of the brain. Since the plasticity of visual cortex appears to be limited in adulthood, we might expect imagery of those with adult-onset low vision to be relatively unaffected by these losses. But if visual imagery is based on recent and current experience, we would expect images of those with low vision to share some properties of impaired visual perception. We examined key parameters of mental images reported by normally sighted subjects, compared to those with early- and late-onset low vision, and with a group of subjects with restricted visual fields using an imagery questionnaire. We found evidence that those with reduced visual acuity report the imagery distances of objects to be closer than those with normal acuity and also depict objects in imagery with lower resolution than those with normal visual acuity. We also found that all low vision groups, like the normally sighted, image objects at a substantially greater distance than when asked to place them at a distance that ‘just fits’ their imagery field (overflow distance). All low vision groups, like the normally sighted, showed evidence of a limited visual field for imagery, but our group with restricted visual fields did not differ from the other groups in this respect. We conclude that imagery of those with low vision is similar to that of those with normal vision in being dependent on the size of objects or features being imaged, but that it also reflects their reduced visual acuity. We found no evidence for a dependence on imagery of age of onset or number of years of vision impairment.     

Vertical-horizontal illusion present for sighted but not early blind humans using auditory substitution of vision

This experiment was undertaken to investigate the effect of sensory modality (vision vs. audition) and of visual status (early blind vs. sighted) on susceptibility to the vertical-horizontal illusion. Early blind volunteers and blindfolded sighted subjects explored variants of the vertical-horizontal illusion using a device that substituted audition for vision, whereas sighted subjects from an independent group inspected the same stimuli visually. Sensitivity to the vertical-horizontal illusion, including an illusion of moderate strength when using the sensory substitution device, was observed only in the two sighted groups. The existence of an illusion effect when using such a device supports the idea of a visual perception provided by sensory substitution, whereas the attenuation of the vertical-horizontal illusion strength is consistent with the visual field shape theory (Künnapas, 1955a). The absence of the illusion effect in early blind subjects suggests that the sensory experience influences the nature of perception and that the visual experience plays a crucial role in the vertical-horizontal illusion, in accordance with the size-constancy scaling theory (Gregory, 1963).     

Behavioral evidence for task-dependent “what” versus “where” processing within and across modalities

Task-dependent information processing for the purpose of recognition or spatial perception is considered a principle common to all the main sensory modalities. Using a dual-task interference paradigm, we investigated the behavioral effects of independent information processing for shape identification and localization of object features within and across vision and touch. In Experiment 1, we established that color and texture processing (i.e., a “what” task) interfered with both visual and haptic shape-matching tasks and that mirror image and rotation matching (i.e., a “where” task) interfered with a feature-location-matching task in both modalities. In contrast, interference was reduced when a “where” interference task was embedded in a “what” primary task and vice versa. In Experiment 2, we replicated this finding within each modality, using the same interference and primary tasks throughout. In Experiment 3, the interference tasks were always conducted in a modality other than the primary task modality. Here, we found that resources for identification and spatial localization are independent of modality. Our findings further suggest that multisensory resources for shape recognition also involve resources for spatial localization. These results extend recent neuropsychological and neuroimaging findings and have important implications for our understanding of high-level information processing across the human sensory systems.     

An examination of the relationship between visual capture and prism adaptation

The phenomena of prismatically induced “visual capture” and adaptation of the hand were compared. In Experiment 1, it was demonstrated that when the subject’s hand was transported for him by the experimenter (passive movement) immediately preceding the measure of visual capture, the magnitude of the immediate shift in felt limb position (visual capture) was enhanced relative to when the subject moved the hand himself (active movement). In Experiment 2, where the dependent measure was adaptation of the prism-exposed hand, the opposite effect was produced by the active/passive manipulation. It appears, then, that different processes operate to produce visual capture and adaptation. It was speculated that visual capture represents an immediate weighting of visual over proprioceptive input as a result of the greater precision of vision and/or the subject’s tendency to direct his attention more heavily to this modality. In contrast, prism adaptation is probably a recalibration of felt limb position in the direction of vision, induced by the presence of a registered discordance between visual and proprioceptive inputs.     

Roughness perception of unfamiliar dot pattern textures

Both vision and touch yield comparable results in terms of roughness estimation of familiar textures as was shown in earlier studies. To our knowledge, no research has been conducted on the effect of sensory familiarity with the stimulus material on roughness estimation of unfamiliar textures.The influence of sensory modality and familiarity on roughness perception of dot pattern textures was investigated in a series of five experiments. Participants estimated the roughness of textures varying in mean center-to-center dot spacing in experimental conditions providing visual, haptic and visual–haptic combined information.The findings indicate that roughness perception of unfamiliar dot pattern textures is well described by a bi-exponential function of inter-dot spacing, regardless of the sensory modality used. However, sensory modality appears to affect the maximum of the psychophysical roughness function, with visually perceived roughness peaking for a smaller inter-dot spacing than haptic roughness. We propose that this might be due to the better spatial acuity of the visual modality. Individuals appeared to use different visual roughness estimation strategies depending on their first sensory experience (visual vs. haptic) with the stimulus material, primarily in an experimental context which required the combination of visual and haptic information in a single bimodal roughness estimate. Furthermore, the similarity of findings in experimental settings using real and virtual visual textures indicates the suitability of the experimental setup for neuroimaging studies, creating a more direct link between behavioral and neuroimaging results.