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.     

Intermodality relations in localization in blind and sighted people

Developmental data were gathered on the relative importance of vision, audition, and proprioception in determining spatial direction in a conflict situation. Age trends did not support the hypothesis that information from different modalities becomes better differentiated with age. In a follow-up study, blind children of different ages were tested under auditory-proprioceptive conflict conditions. No age changes were found. The possibility of a visual involvement in auditory and proprioceptive localization is discussed.     

Spatial memory by blind and sighted children.

Non-verbal recall of haptically presented spatial positions by three age groups of blind and sighted children was tested under conditions varying cueing, recall type and stimulus position in a within-subject design. Slighted status was not only significant, but interacted significantly with recall type, and further with stimulus position, consistent with sequential haptic by blind and quasi-simultaneous visual processing by sighted children. Age was significant, but its only significant interaction was a relatively small one with cueing conditions and stimulus position, suggesting that the oldest group, regardless of sightedness, used verbal strategies in pre-cued conditions. The findings support the hypothesis that visual and haptic modalities of representation have demonstrably different effects on processing and efficiency in spatial recall, but counterindicate the hypothesis that these relate differentially to age. Results also suggest that a combination of cue utilization and verbal strategies is a significant, but relatively minor, factor in improvements in spatial recall.     

Roughness perception in haptic virtual reality for sighted and blind people

Psychophysical functions for perceived roughness, relating ln (magnitude estimate of roughness) to ln (groove width), were obtained for blind and sighted participants in virtual reality using the PHANToM force feedback device. The stimuli were sinusoidal surfaces with groove widths between 0.675 mm and 20.700 mm. Group functions showed a similar nonlinearity to those obtained in physical reality using rigid probes (Klatzky, Lederman, Hamilton, Grindley, & Swendsen, 2003; Lederman, Klatzky, Hamilton, & Ramsay, 1999). Individual functions gave a different picture. Of 23 total participants, there were 13 with wholly descending linear psychometric functions, 7 with quadratic functions similar to the group function, and 3 with anomalous functions. Individual power law exponents showed no significant effects of visual status. All analyses gave a power law exponent close to -0.80. The implications for theories of roughness, methodologies of data analysis, and the design of haptic virtual reality interfaces are considered.     

The effects of curvature on haptic judgments of extent in sighted and blind people

A series of experiments was carried out to examine the effect of curvature on haptic judgments of extent in sighted and blind individuals. Experiment 1 showed that diameters connecting the endpoints of semicircular lines were underestimated with respect to straight lines, but failed to show an effect of visual experience on length judgments. In experiment 2 we tested are lengths. The effects of curvature on perceived path length were weaker, but were still present in this experiment. Visual experience had no effect on path length judgments. Another experiment was performed to examine the effect of repeated tracing (1, 5, 9, or unlimited number of traces) on judgments of the lengths of straight lines and diameters of semicircles. Judgments of extent were more accurate when subjects engaged in larger numbers of traces. There was no effect of number of traces on curve-height judgments, suggesting that subjects were not using height estimates to judge diameters of semicircles. In a further experiment we tested the effect of number of traces on curves that varied in height. Restricting subjects to a single trace magnified the effect of path length on judgments of the distance between the endpoints of curves. Additional experiments showed that curvature effects on diameter judgments were not eliminated when stimuli were in the frontal plane or when the curves were explored with the use of two hands. Arm support had no effect on judged length in experiment 7. A final experiment showed a robust horizontal vertical illusion in haptic perception of convex curves, with overestimation of the heights of the curves compared with their widths. The practical and theoretical implications of the results are discussed.     

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.     

Functional equivalence of spatial images from touch and vision: evidence from spatial updating in blind and sighted individuals

This research examined whether visual and haptic map learning yield functionally equivalent spatial images in working memory, as evidenced by similar encoding bias and updating performance. In 3 experiments, participants learned 4-point routes either by seeing or feeling the maps. At test, blindfolded participants made spatial judgments about the maps from imagined perspectives that were either aligned or misaligned with the maps as represented in working memory. Results from Experiments 1 and 2 revealed a highly similar pattern of latencies and errors between visual and haptic conditions. These findings extend the well-known alignment biases for visual map learning to haptic map learning, provide further evidence of haptic updating, and most important, show that learning from the 2 modalities yields very similar performance across all conditions. Experiment 3 found the same encoding biases and updating performance with blind individuals, demonstrating that functional equivalence cannot be due to visual recoding and is consistent with an amodal hypothesis of spatial images.     

Tactual picture identification by blind and sighted people: Effects of providing categorical information

Four experiments examined the influence of categorical information and visual experience on the identification of tangible pictures, produced with a raised-line drawing kit. In Experiment 1, prior categorical information aided the accuracy and speed of picture identification. In a second experiment, categorical information helped subjects when given after the examination of each picture, but before any attempt at identification. The benefits of categorical information were also obtained in another group of subjects, when the superordinate categories were named at the start of the experiment. In a third experiment, a multiple-choice picture recognition task was used to eliminate the difficulty of naming from the picture-identification task. The multiple-choice data showed higher accuracy and shorter latencies when compared with identification tasks. A fourth experiment evaluated picture identification in blindfolded sighted, early, and late blind participants. Congenitally blind subjects showed lower performance than did the other groups, despite the availability of prior categorical information. The data were consistent with theories that assume that visual imagery aids tactual perception in naming raised line drawings. It was proposed that part of the difficulty in identification of raised line pictures may derive from problems in locating picture categories or names, and not merely in perception of the patterns.     

Spatial biases in peripersonal space in sighted and blind individuals revealed by a haptic line bisection paradigm

Our representation of peripersonal space does not always accurately reflect the physical world. An example of this is pseudoneglect, a phenomenon in which neurologically normal individuals bisect to the left of the veridical midpoint, reflecting an overrepresentation of the left portion of space compared with the right one. Consistent biases have also been observed in the vertical and radial planes. It is an open question whether these biases depend on normal visual experience for their occurrence. Here we systematically investigated this issue by testing blindfolded sighted and early blind individuals in a haptic line bisection task. Critically, we found a robust leftward bias in all participants. In the vertical and radial planes, sighted participants showed a consistent downward and proximal bias. Conversely, the directional bias in blind participants was dependent on the final movement direction; thus, there was no general bias in either direction. These findings are discussed in terms of different reference frames adopted by sighted and blind participants when encoding space.     

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.     

Tactile-kinaesthetic perception of straightness in blind and sighted humans

A comparison is made between the tactile-kinaesthetic perception of straightness in twenty blind and twenty sighted subjects. Both types of subject are found to perceive a “plus curved” edge as straight, but this curve is significantly less for the blind than for the sighted, i.e. the blind subjects' judgments correspond more closely to the objective straight. Furthermore, the blind, both as individuals and as a group, are significantly finer in their judgments and more consistent. These results are thought to be explained in terms of the more highly developed organisation of the blind's tactile-kinaesthetic perception.     

Location and distance estimates by blind and sighted children

Blindfold normal, blindfold autistic and congenitally blind children made reproduction location and distance estimates of an arm movement. For each task they first experienced a standard vertical movement of a predetermined extent. In the test tasks which followed, they either reproduced the movement exactly, reproduced the end point although commencing from a different starting position, or reproduced the same distance from a different starting point. Sighted normal children and blind children performed very similarly on both the reproduction and the location task. However on distance reproduction, the blind children underestimated the longer distances more markedly than did the normals. Autistic children resembled the blind in their attempts to reproduce the longer distances. In addition they had a tendency to overshoot over short distances in all tasks.     

Simple auditory reaction time in blind and sighted adolescents.

This study compared simple auditory reaction times of 20 subjects aged between 11 and 15 yr. (M = 13), 10 born-blind from the Louis Braille Institut (Montréal) and 10 normal sighted subjects of the same age and sex. Their task was to press a telegraph key as fast as possible after presentation of an auditory stimulus. Each subject executed five blocks of 10 trials; the blocks were separated by a rest period of 1 min. The results showed no significant difference (p greater than .05) between born-blind and sighted people of the same sex and chronological age in regard to simple auditory reaction time.     

The structure of haptic space in the blind and sighted

Summary The purpose of the present experiment was to analyse the metric of haptic space. The subjects were shown a goal-point, after having felt the sides of a right triangle with differing lengths. The subjects were then required to estimate the position of the goal-point in one of two ways, either along the hypotenuse from the starting point (a cognitive spatial orientation task) or via the sides touched previously (a perceptual spatial orientation task). They were asked to do this either by making a hand movement which would approximate the distance (motor estimate) or verbally (verbal estimate). There were four groups of subjects: congenitally blind (CB), adventitiously blind (AB), sighted under blindfold (SB), and sighted people with visual pre-orientation (SV). 10 subjects were in each group. The major results of the experiment were: (1) With all groups but SV a distortion was observed in the estimates of the shortest distance from the Euclidian metric to the city-block-metric. (2) The groups AB and SB produced the largest distortion from the Euclidian metric. (3) In the case of motor estimates, both cognitive and perceptual spatial orientation tasks led to congruent metrics. (4) With the exception of group SV verbal and motor estimates led to divergent metrics. The results are considered from the points of view of (a) empiricist theories, (b) theories of equal laws of structure for all sensory modalities, and (c) the hypothesis of transposition.This investigation was supported in part by the German Research Association (Deutsche Forschungsgemeinschaft); head of the research project Prof. Dr. F. Merz.I thank the staff of the Blind Mobility Research Unit of the University of Nottingham for the support in correcting the English translation.