Academic journal article Attention, Perception and Psychophysics

Haptic Concepts in the Blind

Academic journal article Attention, Perception and Psychophysics

Haptic Concepts in the Blind

Article excerpt

We investigated and compared the acquisition of haptic concepts by the blind with the acquisition of haptic concepts by sighted controls. Each subject-blind, sighted but blindfolded, sighted and touching, and sighted only-initially classified eight objects into two categories using a study/test format, followed by a recognition/classification test involving old, new, and prototype forms. Each object varied along the dimensions of shape, size, and texture, with each dimension having five values. The categories were linearly separable in three dimensions, but no single dimension permitted 100% accurate classification. The results revealed that blind subjects learned the categories quickly and comparably with sighted controls. On the classification test, all groups performed equivalently, with the category prototype classified more accurately than the old or new stimuli. The blind subjects differed from the other subjects on the recognition test in two ways: They were least likely to false alarm to novel patterns that belonged to the category but most likely to false alarm to the category prototype, which they falsely called "old" 100% of the time. We discuss these results in terms of current views of categorization.

Research in formal categorization theory has made extensive contributions to our knowledge of human memory and perception. However, formal categorization theory has evolved primarily from studies that have used stimuli that are presented visually. A handful of studies have explored auditory (Aiken, 1969; Rosser, 1967) and kinesthetic concepts. For example, Solso and Raynis (1979) had subjects learn kinesthetic concepts in which arm motions were manipulated to trace out line figures.

Notably lacking in the domain of human categorization is how sighted individuals integrate haptic information into concepts and, more specifically, how individuals who are blind are able to learn object concepts. Haptics, derived from the Greek word haptikos, refers to the sense of touch, and includes all felt sensations derived from contact with texture, pressure, hardness, shape contours, temperature, and so on. A moment's reflection makes it clear that commonplace concepts are acquired from a confluence of modalities, with haptics playing an unknown but likely substantial role. The stroking of fur, the felt conformations of a face, exploring everyday objects, and the carrying of an infant or a small pet all involve commonplace haptic sensations. Early experiences are dominated by haptic influences. For example, infants are more likely to bang hard than soft objects (Lockman & Wright, 1988) and to stroke or finger surfaces on the basis of whether they are smooth or textured (Ruff, 1984). In sighted individuals, identification of commonplace objects is remarkably accurate (Klatzky, Lederman, & Metzger, 1985), and blind and sighted children do not differ in tactile exploratory strategies (Morrongiello, Humphrey, Timney, Choi, & Rocca, 1994). For the blind, haptic feedback is a primary mode of identification, and knowledge representation may be inherently dependent on perception through the haptic modality. Thus, formation of haptic concepts through the haptic modality is an important yet unexplored research direction.

The present study was an exploratory venture into how blind individuals learn and represent concepts when instances are explored through touch alone, contrasting their performance with subjects who were sighted but blindfolded. Two additional control groups were also used: subjects who were allowed to touch and see the objects, and subjects who were allowed to see but not touch the objects. The contrast in performance between sighted but blindfolded subjects and the sighted and touching subjects should tell us what sight adds to the haptic modality in learning concepts; the contrast between sight alone and touch alone provides an assessment of which modality alone better teaches the categories used in the present study. …

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