Correlations between psychophysical magnitude estimates and simultaneously obtained auditory nerve, brain stem and cortical responses to click stimuli in man.

Responses from the auditory nerve, brain stem auditory nuclei and cortex, as well as subjective responses to click stimuli at 10 intensities, were recorded simultaneously in the same human subjects. For various measures of the responses, the power-law exponents of their intensity functions were calculated, along with their statistical significances. The electrophysiological and psycho-physical functions were compared for similarity. On average, the exponents of the intensity functions of amplitudes of the auditory nerve and earlier brain stem responses were highly significant, showing similarity across subjects and similarity with the exponents of the subjective estimates. However, a closer examination proved this similarity to be superficial, since magnitude estimates showed an appreciable intersubject and intersession variability while the auditory nerve and brain stem responses were approximately constant. All other electric response measures either had exponents which were not significant or showed even poorer correlation with the subjective response. It is proposed that the type of electrical activity recorded in this study may not be the proper set of neural parameters which give rise to the loudness estimate.