Stereo perception in callosal agenesis and partial callosotomy.

Stereoperception in two acallosal patients and two partial callosotomy patients was compared with that of three normal subjects. All three patients with the splenium missing, whether due to agenesis or surgical intervention, showed midline deficits and broadly similar profiles; namely, they made few uncrossed midline responses. The patient with partial callosal section but with the splenium almost totally spared performed better at the midline than in the periphery. All degrees of disconnection produced some overall loss of performance, confirming the results of Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987). The results are discussed in the context of earlier reports of human and animal studies of stereoperception. Bearing in mind reports of structural alterations in layer III of the striate cortex in acallosals (Shoumjra, K. et al. Brain Res. 93, 241-252, 1975. Also, Akert, K. et al. Trans. Am. Neurol. Assoc. 79, 151-153, 1954), it is speculated that the specific difficulties encountered by them in handling uncrossed disparities may be due to a marked reduction or absence of far neurones in acallosal brains (Poggio, G. F. and Poggio, T. Ann. Rev. Neurosci. 7, 379-412, 1984). The likely importance of the anterior commissure in the efficient integration of crossed disparity (near neurones) (Cowey, A. In Brain Mechanisms and Spatial Vision, D. Ingle (Editor), NATO Advanced Study Institute Series, Martinus Nijhoff, The Hague, 1985) is seen as a possible explanation of the acallosals relative success in making crossed disparity judgements. The variability of performance in normals documented by Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987) is, not surprisingly, even more marked amongst acallosals.