Electrophysiological and behavioral measurements of spectro-temporal processing: Comodulation masking release

Behavioral experiments using the comodulation masking release (CMR) paradigm indicate that the auditory system is able to encode and compare the temporal characteristics of stimuli across multiple frequency regions. Such processing leads to improved signal detection under certain masking conditions. While there is growing electrophysiological evidence of the coding of temporal patterns at a single spectral region (e.g., the envelope-following response), few electrophysiological studies have demonstrated (directly or indirectly) across-frequency processing of temporal patterns. In the present study, behavioral and electrophysiological estimates of signal detection were obtained in masking conditions that typically lead to a CMR. Detection by normal-hearing human adults was estimated behaviorally using an adaptive staircase technique and electrophysiologically by recording late auditory-evoked potentials (N1-P2). Thresholds were estimated for a 1000-Hz sinusoidal signal (100-ms duration) in the presence of continuous, narrow-band noise maskers. Masker conditions included a single narrow-band noise masker centered at 1000 Hz and maskers composed of five noise bands (centered at 600, 800, 1000, 1200, and 1400 Hz) having either independent or identical (comodulated) temporal envelopes. Behavioral results indicated a masking release of about 8 to 12 dB while physiological estimates revealed somewhat smaller, but substantial, CMRs.