The evoked potential as a measure of perceptual and semantic differences.

This review discusses the information content of perceptual and semantic evoked potentials arising in humans as a result of instantaneous changes in nonverbal and verbal stimuli. The amplitudes of perceptual and semantic evoked potentials were found to correlate positively with subjects' assessments of the differences between these stimuli. Multidimensional scaling matrixes of evoked potential amplitudes and subjective assessments of differences on pairwise substitution of stimuli showed that the actual colors and color names occupied a four-dimensional spherical color space and were encoded by excitation vectors of identical lengths. Color differences were equal to the absolute differences between their excitation vectors, while semantic differences in color names corresponded to the absolute difference vectors represented by long-term color memory traces. These data were reviewed in the framework of a spherical model of cognitive processes.