Morton A. Heller

Picture and Pattern Perception in the Sighted and the Blind: The Advantage of the Late Blind

Two experiments are reported on the contribution of visual experience to tactile perception. In the first experiment, sighted, congenitally blind, and late blind individuals made tactual matches to tangible embossed shapes. In the second experiment, the same subjects attempted tactile identification of raised-line drawings. The three groups did not differ in the accuracy of shape matching, but both groups of blind subjects were much faster than the sighted. Late blind observers were far better than the sighted or congenitally blind at tactile picture identification. Four of the twelve pictures were correctly identified by most of the late blind subjects. The sighted and congenitally blind performed at comparable levels in picture naming. There was no evidence that visual experience alone aided the sighted in the tactile task under investigation, since they performed no better than did the early blind. The superiority of the late blind suggests that visual exposure to drawings and the rules of pictorial representation may help tactile picture identification when combined with a history of tactual experience.

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 touch. 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 ceding of tactual stimuli is not advantageous (or necessary) for texture perception, since touch may hold advantages for the detection of the smoothness of surfaces.

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.

Blind children recognizing tactile pictures respond like sighted children given guidance in exploration

Theory of tactile pictures argues that untrained blind subjects can recognize raised, outline pictures. It contends the blind persons knowledge of the shapes of common objects is like that of the sighted, and the blind persons pictorial abilities use the same principles as the sighted persons. To test this theory, blind children (aged 8-13) and blindfolded age-matched sighted children were asked to identify raised-line drawings of common objects. Their performances were correlated. In addition, the blind children identified more than sighted children exploring the pictures actively, but the same number of pictures as sighted children who were given passive, guided exploration. We argue blind and sighted children use the same principles to identify the pictures, but the blind have superior exploration skills. The differences in the effects of exploration skills on recognition scores are minimized when the sighted children are given guidance, since the sighted children then have efficient contact with the displays, and the performance of the sighted and the blind is then governed by the same principles, without one group benefitting from advantages in exploration skills.

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.

Perspective taking, pictures, and the blind

Congenitally blind, late blind, and blindfolded sighted controls attempted a Piagetian perspectivetaking (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.

Tactile picture perception in sighted and blind people

This paper reviews recent research on the perception of tangible pictures by sighted people and those who are blind or have extremely low vision. Raised-line pictures are useful for evaluating spatial cognition in congenitally blind people. The ease or difficulty of picture recognition is shown to vary with complexity, familiarity, and categorical information. Blind people are able to use pictorial displays effectively, but may benefit from instruction when complex depictions of three-dimensional objects involve foreshortening.

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 identical 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 inter-sensory 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.

Production and Interpretation of Perspective Drawings by Blind and Sighted People

In three experiments the production and interpretation of perspective drawings by blind and sighted subjects were examined. Blindfolded sighted, early-blind, and late-blind subjects first attempted to produce raised-line drawings of a surface at a number of angles—0° (panel horizontal), −22.5°, −45°, −67.5°, and −90° (vertical). Congenitally blind subjects did not show foreshortening in their naive raised-line drawings. However, the congenitally blind subjects were able to understand aspects of perspective, and performed as well as the blindfolded sighted and late-blind subjects in a subsequent multiple-choice task. Subjects in the multiple-choice task were required to match tangible perspective drawings to a slanted board. Although the three groups performed alike, both groups of blind subjects performed better than blindfolded sighted controls on judgments involving drawings of the vertical panel in the second experiment. In a final experiment, in which vision and touch were compared, sighted subjects were required to adjust the angle of the panel to match foreshortened, perspective drawings. This experiment yielded significantly better performance with vision than with touch, but only for drawings of the board at the vertical orientation. The results suggested that congenitally blind people may benefit from haptic exposure to raised-line configurations representing geometric perspective.

Haptic Dominance in Form Perception with Blurred Vision

Three experiments are reported in which subjects were exposed to discrepant visual and haptic form information. Stained glass was used to blur vision and lower its accuracy close to the level of touch. Haptic dominance occurred with the large intersensory conflicts under study. It is proposed that touch may be dominant in form perception when vision is peripheral and blurry.