Diderot Reconsidered: Visual Impairment and Auditory Compensation

Two general models for auditory compensation attending visual loss, structural and strategic, are discussed in the light of available research. It is suggested that previous dismissals of structural forms of auditory compensation may be in error, at least for those who are more profoundly and congenitally impaired.

Perceiving space and optical cues via a visuo-tactile sensory substitution system: a methodological approach for training of blind subjects for navigation

A methodological approach to perceptual learning was used to allow both early blind subjects (experimental group) and blindfolded sighted subjects (control group) to experience optical information and spatial phenomena, on the basis of visuo-tactile information transmitted by a 64-taxel pneumatic sensory substitution device. The learning process allowed the subjects to develop abilities in spatial localisation, shape recognition (with generalisation to different points of view), and monocular depth cue interpretation. During the training phase, early blind people initially experienced more difficulties than blindfolded sighted subjects (having previous perceptual experience of perspective) with interpreting and using monocular depth cues. The amelioration of the performance for all blind subjects during training sessions and the quite similar level of performance reached by two groups in the final navigation tasks suggested that early blind people were able to develop and apply cognitive understanding of depth cues. Both groups showed generalisation of the learning from the initial phases to cue identification in the maze, and subjectively experienced shapes facing them. Subjects' performance depended not only on their perceptual experience but also on their previous spatial competencies.

Visual mediation and the haptic recognition of two-dimensional pictures of common objects

A set of three experiments was performed to investigate the role of visual imaging in the haptic recognition of raised-line depictions of common objects. Blindfolded, sighted (Experiment 1) observers performed the task very poorly, while several findings converged to indicate that a visual translation process was adopted. These included (1) strong correlation between image-ability ratings (obtained in Experiment 1 and, independently, in Experiment 2) and both recognition speed and accuracy, (2) superior performance with, and greater ease of imaging, two-dimensional as opposed to three-dimensional depictions, despite equivalence in rated line complexity, and (3) a significant correlation between the general ability of the observer to image and obtained imageability ratings of the stimulus depictions. That congenitally blind observers performed the same task even more poorly, while their performance did not differ for two- versus three-dimensional depictions (Experiment 3), provides further evidence that visual translation was used by the sighted. Such limited performance is contrasted with the considerable skill with which real common objects are processed and recognized haptically. The reasons for the general difference in the haptic performance of two- versus three-dimensional tasks are considered. Implications for the presentation of spatial information in the form of tangible graphics displays for the blind are also discussed.