Blind people must adjust by using their remaining senses to interact with their environment. Adjustments occur even in adults with late-onset blindness and transiently in visually deprived sighted individuals. Section 6.18.1 discusses reading braille as an example adjustment that depends on information transmitted from specific mechanoreceptors in the fingertips. When blind people learn to discriminate subtle patterns of raised dots and to translate these into linguistic information, they extensively practice motor and perceptual skills. Additionally, blind people must utilize nonvisual information in all aspects of daily existence. As a consequence, blind individuals exhibit performance advantages in attending to touch. They also excel at several auditory tasks, but these skills will not be considered here. Section 6.18.2 argues that heightened acuity occurs in tasks that require practice in processing tactile information. Furthermore, prior visual experience influences, especially, spatial perception, and this impacts the artistic and spatial cognitive skills of blind people. Section 6.18.3 reviews the evidence that an expanded somatosensory cortex representation for the braille reading finger(s) in blind people is an example alteration that possibly underlies enhanced tactile acuity. However, findings in blind people do not consistently indicate somatosensory cortex reorganization, nor do they reveal an underlying Hebbian mechanism of enhanced synaptic efficacy. Section 6.18.4 explores evidence of more dramatic plasticity - cross-modal tactile and auditory inputs activating visually deprived occipital cortex. Visual deprivation, whether permanent in blind people or transient through blindfolding sighted persons, apparently does not silence visual cortex, which adjusts by processing nonvisual modalities. A significant question is whether altered visual cortex activity provides for relevant adjustments to blindness. Evidence is reviewed regarding which perceptual and cognitive processes activate visual cortex in early- and late-onset blind people. An important issue is whether reorganized visual cortex follows functional subdivisions that resemble those identified in sighted people. Section 6.18.5 examines whether inherent capabilities, unmasked by visual deprivation, contribute to visual cortex plasticity and whether cross-modal responses reflect new or physiologically altered connections. Possible anatomical and physiological sources of cross-modal inputs to visual cortex are described. However, limited evidence links these to explicit visual cortex reorganization in blindness. A mostly hypothetical discussion considers whether visual cortex reorganizes through changes in effective intracortical connectivity from multisensory areas.
- Magnetic resonance imaging