Objective correlates of pitch salience using pupillometry

Although objective correlates of pitch salience have been investigated in several neuroimaging studies, the results remain controversial. In the present study, a novel approach to objectively estimate pitch salience was used. Pupil dilation was measured as an indicator of the required effort in performing a pitch discrimination task for complex tones of varying pitch salience.

It has been shown that cognitive processing demands of the task can be reflected in the pupil response, whereby pupil size dilates when cognitive load increases. The hypothesis was that pupil size would increase with increasing effort in performing the task and thus with decreasing pitch salience. A group of normal-hearing listeners first performed a behavioral pitch-discrimination experiment, where fundamental frequency difference limens ( F 0 DLs ) were measured as a function of F 0 .

Results showed that pitch salience of complex tones filtered in a high spectral region (1.5-3.5 kHz) increased with F 0 . In a second experiment, listeners were presented with trials containing two reference complex tones with a fixed F 0 and a deviant tone with a larger F 0 . Six conditions with different salience, defined by both the frequency region and F 0 , were considered.

Pupil size was measured for each condition, while the subjects’ task was to detect the deviants by pressing a response button. The expected trend was that pupil size would increase with decreasing salience. Results for musically trained listeners showed the expected trend, whereby pupil size significantly increased with decreasing salience of the stimuli.

Non-musically trained listeners showed, however, a smaller pupil size for the least salient condition as compared to a medium salient condition, probably due to a too demanding task