Physiological (waves I and V) and psychophysical tuning curves in human subjects

Tuning curves obtained on wave I (VIII nerve) and wave V of the auditory brainstem response were recorded simultaneously with ear-canal and forehead electrodes. On these same human subjects using the same acoustic stimuli psychophysical tuning curves were also measured. For each subject the three tuning curves were qualitatively similar; however, both intra- and inter-subject quantitative differences were present. The best agreement was between the psychological and the wave V tuning curves. The wave I tuning curve differed from the other two mainly on the high-frequency side by showing a wider response area. The main difference between both physiological tuning curves and the psychophysical tuning curve occurred near center frequency of the probe signal: Physiological tuning curves had deeper tips in comparison to the psychophysical tuning curves which had shallow rounded tips. This might be due to energy splatter of the short-duration signal which can significantly effect psychophysical judgments while minimally contributing to the physiological responses. A precise measure of sharpness of tuning was difficult to obtain; however, the response area of wave I appears to be more biased towards high-frequency cochlear neurons than either wave V or psychophysical judgments. Tuning curves are shown to be a viable method of relating physiological to psychophysical measurements in human subjects.