Cross-modal plasticity of tactile perception in blindness

Abstract

This review focusses on cross-modal plasticity resulting from visual deprivation. This is viewed against the background of task-specific visual cortical recruitment that is routine during tactile tasks in the sighted and that may depend in part on visual imagery. Superior tactile perceptual performance in the blind may be practice-related, although there are unresolved questions regarding the effects of Braille-reading experience and the age of onset of blindness. While visual cortical areas are clearly more involved in tactile microspatial processing in the blind than in the sighted, it still remains unclear how to reconcile these tactile processes with the growing literature implicating visual cortical activity in a wide range of cognitive tasks in the blind, including those involving language, or with studies of short-term, reversible visual deprivation in the normally sighted that reveal plastic changes even over periods of hours or days.

Figure 1

Lateral view of inflated representation (bottom) and flat map (middle) of the right hemisphere (RH) showing location of CIP activity in normally sighted subjects that was selective for tactile microspatial (offset) discrimination, relative to tactile temporal (stimulus duration) discrimination, and whose activation magnitude in the offset task (relative to rest) predicted tactile acuity threshold. Scale represents correlation coefficient (r) of this predictive relationship. The negative correlation indicates that greater activation magnitudes were associated with lower thresholds (better acuity). Time-courses of blood oxygenation level-dependent (BOLD) signal at the CIP focus in the spatial and temporal tasks (top) demonstrate spatial selectivity. Time axis is in terms of the number of scans (each scan comprised 1.5 s). Based on data in Stilla et al. (2007). A: anterior; P: posterior.

Figure 2

Flat maps (top) and lateral views of inflated representations (bottom) of the right and left hemisphere (RH, LH) showing regions whose activation magnitude in the offset task (relative to rest) predicted tactile acuity threshold in a group of blind subjects including early and late blind. Scale represents correlation coefficient (r) of this predictive relationship. Modified from Stilla et al. (2008b). Abbreviations in Figures 1&2 refer to areas discussed in the text.

Figure 3

Time-courses of BOLD signal at selected foci from Figure 2, in the spatial (offset) and temporal (stimulus duration) tasks. These foci were spatially selective in both early blind (EB) and late blind (LB). Modified from Stilla et al. (2008b).