Haptic perception of the horizontal by blind and low-vision individuals.

We examined haptic perception of the horizontal in visually impaired people. Blind people (late blind and congenitally blind), persons with very low vision, and blindfolded sighted individuals felt raised-line drawings of jars at four angles. They had to demonstrate their understanding that water remains horizontal, despite jar tilt, by selecting the correct raised-line drawing given four choices. Low-vision subjects, with near perfect scores, performed significantly better than the other groups of subjects. While the late-blind and blindfolded sighted subjects performed slightly better than the congenitally blind participants, the difference between the late-blind and congenitally blind groups was nonsignificant. The performance of the congenitally blind subjects indicates that visual experience is not necessary for the development of an understanding that water level stays horizontal, given container tilt.     

Perception of weight and volume of functional objects as judged by the sighted and blind

Summary The manner in which sighted, sighted-but-blindfolded, late-blind (subsequent to 7 years of age), and congenitally blind (blind since birth) persons employ physical parameters in determining weight and volume of functional objects was studied. Eight stimuli each having a unique combination of physical specifications were judged, using both a match and estimate procedure. The results indicated that information derived from mass, displacement, and density provides the basis for volumetric and weight judgements of sighted persons. Non-sighted individuals employ this information differently than do sighted persons. Likewise, individuals after 7 years of age retain information provided by early visual experience and thus may employ a combination of kinesthetic and visual cues. The results also show that sighted and late-blind groups may employ visual perception or memory in determining volume, whereas sighted-but-blindfolded persons and the congenitally blind may employ mass in volumetric tasks. All groups may employ mass (and perhaps density) in determining weight, and although the weight judgements of non-sighted groups correlate highly with mass, sighted subjects are more accurate in judgement (i.e. have the smaller constant error). Sighted subjects apparently employ a complex system in determining weight. Age at which blindness occurred and the number of years of blindness had no effect for the late-blind group.     

Mental imagery,reasoning, and blindness

Although reasoning seems to be inextricably linked to seeing in the “mind's eye”, the evidence is equivocal. In three experiments, sighted, blindfolded sighted, and congenitally totally blind persons solved deductive inferences based on three sorts of relation: (a) visuo-spatial relations that are easy to envisage either visually or spatially, (b) visual relations that are easy to envisage visually but hard to envisage spatially, and (c) control relations that are hard to envisage both visually and spatially. In absolute terms, congenitally totally blind persons performed less accurately and more slowly than the sighted on all such tasks. In relative terms, however, the visual relations in comparison with control relations impeded the reasoning of sighted and blindfolded participants, whereas congenitally totally blind participants performed the same with the different sorts of relation. We conclude that mental images containing visual details that are irrelevant to an inference can even impede the process of reasoning. Persons who are blind from birth—and who thus do not tend to construct visual mental images—are immune to this visual-impedance effect.     

Mental imagery, reasoning, and blindness

Although reasoning seems to be inextricably linked to seeing in the “mind's eye”, the evidence is equivocal. In three experiments, sighted, blindfolded sighted, and congenitally totally blind persons solved deductive inferences based on three sorts of relation: (a) visuo-spatial relations that are easy to envisage either visually or spatially, (b) visual relations that are easy to envisage visually but hard to envisage spatially, and (c) control relations that are hard to envisage both visually and spatially. In absolute terms, congenitally totally blind persons performed less accurately and more slowly than the sighted on all such tasks. In relative terms, however, the visual relations in comparison with control relations impeded the reasoning of sighted and blindfolded participants, whereas congenitally totally blind participants performed the same with the different sorts of relation. We conclude that mental images containing visual details that are irrelevant to an inference can even impede the process of reasoning. Persons who are blind from birth—and who thus do not tend to construct visual mental images—are immune to this visual-impedance effect.     

Structural properties of spatial representations in blind people: Scanning images constructed from haptic exploration or from locomotion in a 3-D audio virtual environment

When people scan mental images, their response times increase linearly with increases in the distance to be scanned, which is generally taken as reflecting the fact that their internal representations incorporate the metric properties of the corresponding objects. In view of this finding, we investigated the structural properties of spatial mental images created from nonvisual sources in three groups (blindfolded sighted, late blind, and congenitally blind). In Experiment 1, blindfolded sighted and late blind participants created metrically accurate spatial representations of a small-scale spatial configuration under both verbal and haptic learning conditions. In Experiment 2, late and congenitally blind participants generated accurate spatial mental images after both verbal and locomotor learning of a full-scale navigable space (created by an immersive audio virtual reality system), whereas blindfolded sighted participants were selectively impaired in their ability to generate precise spatial representations from locomotor experience. These results attest that in the context of a permanent lack of sight, encoding spatial information on the basis of the most reliable currently functional system (the sensorimotor system) is crucial for building a metrically accurate representation of a spatial environment. The results also highlight the potential of spatialized audio-rendering technology for exploring the spatial representations of visually impaired participants.     

Haptic orientation perception benefits from visual experience: evidence from early-blind, late-blind, and sighted people

Early-blind, late-blind, and blindfolded sighted participants were presented with two haptic allocentric spatial tasks: a parallel-setting task, in an immediate and a 10-sec delay condition, and a task in which the orientation of a single bar was judged verbally. With respect to deviation size, the data suggest that mental visual processing filled a beneficial role in both tasks. In the parallel-setting task, the early blind performed more variably and showed no improvement with delay, whereas the late blind did improve, but less than the sighted did. In the verbal judgment task, both early- and late-blind participants displayed larger deviations than the sighted controls. Differences between the groups were absent or much weaker with respect to the haptic oblique effect, a finding that reinforces the view that this effect is not of visual origin. The role of visual processing mechanisms and visual experience in haptic spatial tasks is discussed.     

Tangible pictures: viewpoint effects and linear perspective in visually impaired people

Perception of raised-line pictures in blindfolded-sighted, congenitally blind, late-blind, and low-vision subjects was studied in a series of experiments. The major aim of the study was to examine the value of perspective drawings for haptic pictures and visually impaired individuals. In experiment 1, subjects felt two wooden boards joined at 45 degrees, 90 degrees, or 135 degrees, and were instructed to pick the correct perspective drawing from among four choices. The first experiment on perspective found a significant effect of visual status, with much higher performance by the low-vision subjects. Mean performance for the congenitally blind subjects was not significantly different from that of the late-blind and blindfolded-sighted subjects. In a further experiment, blindfolded subjects drew tangible pictures of three-dimensional (3-D) geometric solids, and then engaged in a matching task. Counter to expectations, performance was not impaired for the 3-D drawings as compared with the frontal viewpoints. Subjects were also especially fast and more accurate when matching top views. Experiment 5 showed that top views were easiest for all of the visually impaired subjects, including those who were congenitally blind. Experiment 5 yielded higher performance for 3-D than frontal viewpoints. The results of all of the experiments were consistent with the idea that visual experience is not necessary for understanding perspective drawings of geometrical objects.     

Obstacle Crossing Differences Between Blind and Blindfolded Subjects After Haptic Exploration

Little is known about the ability of blind people to cross obstacles after they have explored haptically their size and position. Long-term absence of vision may affect spatial cognition in the blind while their extensive experience with the use of haptic information for guidance may lead to compensation strategies. Seven blind and 7 sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed an obstacle after a haptic exploration. Blind and blindfolded subjects used different strategies to cross the obstacle. After the first 20 trials the blindfolded subjects reduced the distance between the foot and the obstacle at the toe-off instant, while the blind behaved as the subjects with full vision. Blind and blindfolded participants showed larger foot clearance than participants with vision. At foot landing the hip was more behind the foot in the blindfolded condition, while there were no differences between the blind and the vision conditions. For several parameters of the obstacle crossing task, blind people were more similar to subjects with full vision indicating that the blind subjects were able to compensate for the lack of vision.     

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.     

Memory processing of spatial order as transmitted by auditory information in the absence of visual cues

Two experiments were conducted concerning spatial order recall when spatial information is transmitted by auditory stimuli. Temporal order either was congruent with spatial order or was independent of spatial order. In Experiment 1, the comparisons were among normally or partially sighted subjects allowed to look, normally sighted subjects who were blindfolded, and blind children. The main findings were a superiority of the sighted subjects allowed to look (that is, to support auditory information with visual cues) and a smaller advantage for the sighted-but-blindfolded subjects, relative to the blind group. In Experiment 2, normally sighted adults (either seeing or blindfolded) and blind adults were tested. Surprisingly, the blind were not worse than the sighted in this study. Subsequent interviews and detailed analysis of errors suggested that the blind coded spatial information kinesthetically. These indirect analyses also suggested that whereas spatial order was coded temporally in the sighted, it was controlled by both temporal and spatial factors in the blind and blindfolded subjects.     

Sequential vs simultaneous encoding of spatial information: a comparison between the blind and the sighted

The aim of this research is to assess whether the crucial factor in determining the characteristics of blind people's spatial mental images is concerned with the visual impairment per se or the processing style that the dominant perceptual modalities used to acquire spatial information impose, i.e. simultaneous (vision) vs sequential (kinaesthesis). Participants were asked to learn six positions in a large parking area via movement alone (congenitally blind, adventitiously blind, blindfolded sighted) or with vision plus movement (simultaneous sighted, sequential sighted), and then to mentally scan between positions in the path. The crucial manipulation concerned the sequential sighted group. Their visual exploration was made sequential by putting visual obstacles within the pathway in such a way that they could not see simultaneously the positions along the pathway. The results revealed a significant time/distance linear relation in all tested groups. However, the linear component was lower in sequential sighted and blind participants, especially congenital. Sequential sighted and congenitally blind participants showed an almost overlapping performance. Differences between groups became evident when mentally scanning farther distances (more than 5m). This threshold effect could be revealing of processing limitations due to the need of integrating and updating spatial information. Overall, the results suggest that the characteristics of the processing style rather than the visual impairment per se affect blind people's spatial mental images.     

Perspective taking, pictures, and the blind

Congenitally blind, late blind, and blindfolded sighted controls attempted a Piagetian perspective-taking (three-mountain) task. Piaget used the term perspective to mean point of view (Piaget & Inhelder, 1967, p. 210), and the present usage does not imply linear perspective. Subjects used raised-line drawings to depict alternative points of view of an array of three geometric solid forms (cube, cone, and ball). They then identified the point of view of raised-line drawings. The effect of visual status on accuracy was nonsignificant for both response measures. Using alternating vision of the array and drawings, sighted subjects in a control condition performed like the congenitally blind. However, congenitally blind individuals did require more time than the other subjects for the perspective-taking task. In an additional experiment, no difference was found between the three groups in the accuracy or speed of tactile shape matching. The results suggest that visual imagery and visual experience are not necessary for tactile perspective taking.     

Egocentric/allocentric and coordinate/categorical haptic encoding in blind people

In this research, the impact of visual experience on the capacity to use egocentric (body-centered) and allocentric (object-centered) representations in combination with categorical (invariant non-metric) and coordinate (variable metric) spatial relations was examined. Participants memorized through haptic (congenitally blind, adventitiously blind, and blindfolded) and haptic + visual (sighted) exploration triads of 3D objects and then they were asked to judge: "which object was closest/farthest to you?" (egocentric-coordinate); "which object was on your left/right?" (egocentric-categorical); "which object was closest/farthest to a target object (e.g., cone)?" (allocentric-coordinate); "which object was on the left/right of the target object (e.g., cone)?" (allocentric-categorical). The results showed a slowdown in processing time when congenitally blind people provided allocentric-coordinate judgments and adventitiously blind people egocentric-categorical judgments. Moreover, in egocentric judgments, adventitiously blind participants were less accurate than sighted participants. However, the overall performance was quite good and this supports the idea that the differences observed are more quantitative than qualitative. The theoretical implications of these results are discussed.     

Conservation by the congenitally blind

A conservation study of amount using specially designed wire cylinders was made of congenitally blind children and two control groups of sighted children (one of which undertook the task blindfolded), matched for chronological age. No differences were found among the three groups on the age of attainment of conservation. However, the manner by which the blind processed the environment differed from the blindfolded sighted children, as evidenced in some of their non-conservation answers. The language of the blind children did not differ from that of the sighted children in describing the materials, but the language of the non-conserving children of all groups differed from that of conserving children. The importance for several theoretical views on the attainment of conservation is discussed, and it is argued that the achievement of the beginning of operational thinking may be more a central developmental phenomenon than one based on specific sensory experience.     

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.     

Mental rotation and the frame of reference in blind and sighted individuals

Mental rotation in the congenitally blind was investigated with a haptic letter-judgment task. Blind subjects and blindfolded, sighted subjects were presented a letter in some orientation between 0° to 300° from upright and timed while they judged whether it was a normal or mirror-image letter. Both groups showed an increasing response time with the stimulus’s departure from upright; this result was interpreted as reflecting the process of mental rotation. The results for the blind subjects suggest that mental rotation can operate on a spatial representation that does not have any specifically visual components. Further research showed that for the sighted subjects in the haptic task, the orientation of a letter is coded with respect to the position of the hand. Sighted subjects may code the orientation of the letter and then translate this code into a visual representation, or they may use a spatial representation that is not specifically visual.     

The influence of visual experience on visual and spatial imagery

Differences are reported between blind and sighted participants on a visual-imagery and a spatial-imagery task, but not on an auditory-imagery task. For the visual-imagery task, participants had to compare object forms on the basis of a (verbally presented) object name. In the spatial-imagery task, they had to compare angular differences on the basis of the position of clock hands on two clock faces, again only on the basis of verbally presented clock times. Interestingly, there was a difference between early-blind and late-blind participants on the visual-imagery and the spatial-imagery tasks: late-blind participants made more errors than sighted people on the visual-imagery task, while early-blind participants made more errors than sighted people on the spatial-imagery task. This difference suggests that, for visual (form) imagery, people use the channel currently available (haptic for the blind; visual for the sighted). For the spatial-imagery task in this study reliance on haptic processing did not seem to suffice, and people benefited from visual experience and ability. However, the difference on the spatial-imagery task between early-blind and sighted people in this study might also be caused by differences in experience with the analogue clock faces that formed the basis for the spatial judgments.