Loss of a Sense: Effect on Others, Psychological

Generalized Deficiency or Across-Sense Enhancement?

Loss of a sense dramatically alters the type of experience that individuals can rely on as they navigate their world. Some have argued that this is likely to have a negative impact on the sense-deprived individual. Such a view holds that normal development requires integration of information from the different senses, such as when one connects what is being said (audition) with the shape formed by the lips of the speaker (vision). In the absence of such integration, some have argued that development of the remaining senses is compromised and cognitive functioning as a whole is challenged.

Studies of animals and humans show, however, that the loss of one sense is often met by an enhancement of the remaining senses, a phenomenon called cross-modal plasticity. For example, cats blinded early in life are better at localizing the source of a sound. They also show enhanced growth of facial whiskers resulting in larger areas of the somatosensory cortex dedicated to tactile exploration. Such compensatory mechanisms often result in deprived individuals outperforming their non-deprived peers on tasks involving their remaining senses. As outlined in this entry, enhanced performance is not systematic. Rather, enhancements in the remaining modalities are most marked under conditions of attention, when the task requires selecting a target from among distractors, or when the time and place of occurrence of the target are unknown. The consequences of these changes for how individuals perceive, remember, and think are being worked out.

The work discussed in this entry only applies to those individuals who have completely lost access to one of their senses early in life, have no associated brain damage, and have been given the opportunity to develop adequate social and communication skills. These selection criteria are necessary to study the effect of sensory loss itself, without being confounded by effects of brain disorder or atypical [Page 534]social development. Thus, most research focuses on blindness caused by early vision loss in both eyes or on deafness caused by profound hearing loss in both cochleas. Although this restricts the relevance of the work to only a small subpopulation of deaf or blind individuals, the focus on early and total deprivation is not arbitrary. It is necessary because brain changes after early deprivation are more widespread. Similarly, brain changes after total sensory loss are more profound and of a different nature than are those observed after partial sensory loss. As research matures, it is encompassing the situation of a greater number of individuals, documenting which mechanisms of brain plasticity are shared by different amounts and onsets of deprivation and which ones may be specific to early and total loss.

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