Frequency dependence of sensitivity to interaural phase differences in pure tones

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Human Hearing Physiology

Background:

• Established knowledge indicates a sharp increase in interaural time difference (ITD) thresholds for pure tones above 1300 Hz in humans, with unmeasurability above 1400 Hz.
• Existing physiological data and auditory models suggest a more gradual decline in auditory sensitivity, masked by psychometric function characteristics.
• Previous studies reported ITD thresholds at specific correct proportions but lacked data on the decline of sensitivity or d' with increasing frequencies.

Purpose of the Study:

• To investigate the precise decline in pure-tone auditory sensitivity at higher frequencies in humans.
• To compare behavioral data with existing auditory models and physiological data on auditory nerve fiber function.
• To characterize the rate of sensitivity loss in dB/octave.

Main Methods:

• Collected pure-tone behavioral data using a constant stimulus procedure.
• Assessed auditory sensitivity by measuring the proportion of correct responses.
• Analyzed data from nine human subjects to determine sensitivity decline across frequencies.

Main Results:

• Seven out of nine subjects demonstrated high proportions correct (>0.9) at 1300 Hz.
• Subjects exhibited near-zero sensitivity (proportion correct near chance level) at 1500 Hz.
• Observed auditory sensitivity decline ranged from 46-78 dB/octave, significantly steeper than model predictions.

Conclusions:

• The rate of auditory sensitivity decline in humans at high frequencies is considerably steeper than previously predicted by auditory models.
• The findings suggest limitations in current models of auditory processing and phase locking in auditory nerve fibers.
• This study provides crucial behavioral data highlighting a more abrupt loss of high-frequency auditory sensitivity than anticipated.