TACTILE MENTAL-IMAGERY IN SIGHTED PERSONS AND IN PATIENTS SUFFERING FROM PERIPHERAL BLINDNESS EARLY IN LIFE

Patterns of cortical activity as measured by scalp-recorded event-rela ted slow negative DC potential shifts were recorded in 9 early blind a nd 23 sighted normals while they imagined the feel of textures with th e fingertips of one hand. All sighted subjects reported to have concom itant visual imagery as well. Hence, it was not surprising to observe occipital negative shifts, previously described as a sign of occipital Visual cortex involvement in visual mental imagery. Though having nev er had visual perception, the blind, too, had occipital negativities. Their absolute amplitudes were smaller than in the sighted, not only o ccipitally but also and more pronounced at other areas, particularly f rontally where amplitudes were even positive. On the hypothesis that t he smaller overall amplitudes in the blind could obscure topographical differences betweeen groups, the relative distribution of negativity across the scalp was assessed, using normalized data. Such normalized parameters significantly differed between groups, indicating that the occipital potentials of the blind were relatively more negative as rel ated to the other scalp areas, than were the occipital potentials of t he sighted as related to the other scalp areas. This occipital finding might indicate a participation of the blind's visually deprived occip ital cortex in tactile imagery. Second, parietal DC potentials were ma ximal over the hemisphere contralateral to the imaging hand, possibly indicating involvement of the contralateral parietal association corte x in tactile imagery. Reasons why this was true only for the sighted, are discussed.