Sensitivity to Envelope Interaural Time Differences: Modeling Auditory Modulation Filtering

Area of Science:

• Auditory neuroscience
• Computational modeling
• Psychoacoustics

Background:

• Envelope interaural time difference (ITD_ENV) is a cue for sound localization.
• ITD_ENV is processed by excitatory-inhibitory (EI) neurons in the lateral superior olive (LSO).
• Human sensitivity to ITD_ENV varies and decreases with carrier frequency and modulation rate.

Purpose of the Study:

• To computationally model the variable sensitivity to ITD_ENV across human listeners.
• To investigate the role of LSO neuron membrane frequency responses in ITD_ENV sensitivity variation.
• To understand ITD_ENV processing at different modulation rates and carrier frequencies.

Main Methods:

• Developed a bilateral auditory-periphery model stimulating EI neurons.
• Modeled LSO neuron membrane frequency response ranges to simulate listener variability.
• Calculated just-noticeable differences in ITD_ENV using Fisher information from model spike-rate functions.

Main Results:

• Model populations with decreasing frequency response ranges reproduced human ITD_ENV sensitivity variations.
• Model populations matched human sensitivity at progressively higher modulation rates.
• Fast resonant model neurons extended ITD_ENV sensitivity above 500 Hz.

Conclusions:

• LSO neuron membrane frequency response range is a key factor in variable ITD_ENV sensitivity.
• Computational models can replicate human psychoacoustic performance in ITD_ENV processing.
• Modulation filtering by membrane impedance shapes ITD_ENV encoding in the auditory brainstem.