Forward masking in the amplitude-modulation domain for tone carriers: Psychophysical results and physiological correlates

Magdalena Wojtczak, Paul C. Nelson, Neal F. Viemeister, Laurel H. Carney

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Wojtczak and Viemeister (J Acoust Soc Am 118:3198-3210, 2005) demonstrated forward masking in the amplitude-modulation (AM) domain. The present study examined whether this effect has correlates in physiological responses to AM at the level of the auditory midbrain. The human psychophysical experiment used 40-Hz, 100% AM (masker AM) that was imposed on a 5.5-kHz carrier during the first 150 ms of its duration. The masker AM was followed by a 50-ms burst of AM of the same rate (signal AM) imposed on the same (uninterrupted) carrier, either immediately after the masker or with a delay. In the physiological experiment, single-unit extracellular recordings in the awake rabbit inferior colliculus (IC) were obtained for stimuli designed to be similar to the uninterrupted-carrier conditions used in the psychophysics. The masker AM was longer (500 ms compared with 150 ms in the psychophysical experiment), and the carrier and modulation rate were chosen based on each neuron's audio- and envelope-frequency selectivity. Based on the average discharge rates of the responses or on the temporal correlation between neural responses to masked and unmasked stimuli, only a small subset of the population of IC cells exhibited suppression of signal AM following the masker. In contrast, changes in the discharge rates between the temporal segments of the carrier immediately preceding the signal AM and during the signal AM varied as a function of masker-signal delay with a trend that matched the psychophysical results. Unless the physiological observations were caused by species differences, they suggest that stages of processing higher than the IC must be considered to account for the AM-processing time constants measured perceptually in humans.

Original languageEnglish (US)
Pages (from-to)361-373
Number of pages13
JournalJARO - Journal of the Association for Research in Otolaryngology
Volume12
Issue number3
DOIs
StatePublished - Jun 2011

Keywords

  • modulation coding in the inferior colliculus
  • recovery from modulation masking

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