Psychophysics with the split-brain subject: on hemispheric differences and numerical mediation in perceptual matching tasks.

Almtraet--Two questions concerning the mediation of psychophysical scaling of lateralized stimuli were investigated in .commissurotomized patients: (I) Is cross modality matching mediated by subvocal number assignment? (II) Are there hemispheric differences in psychophysical scaling? When exponents of power functions characterizing the magnitude estimation of joint position in right and left hands and line length in right and left visual fields were compared between the hemispheres, only the left hemisphere was able to make such judgments. When exponents of functions characterizing the cross modality matching of these stimuli were compared between the hemispheres, there were no sim~ificant differences. These results argue against mediation of cross modnlity matching by subvocai number a s s i ~ n t , and this demonstration of symmetrical tramduction of univariate stimuli suggests a reinterpretation of the literature reporting perceptual asymmetries.