A physiological study of forward masking: Recovery of discharge rate to probe tones in inferior colliculus

Abstract

In forward masking the perception of a target sound (probe) is degraded due to the presence of a preceding sound (masker). Two factors contributing to the probe response are (i) the temporal separation (delay) between the masker and probe and (ii) the interstimulus interval (ISI). Human listeners recover from forward masking to quiet probe thresholds for delays of 150–300 ms [Jesteadt et al., JASA 71, 950 (1982)]. Similarly, physiological studies have reported neural correlates of behavioral forward masking at the level of the inferior colliculus (IC), with 300-ms recovery of neural thresholds to the probe [Nelson et al., J. Neurosci. 29, 2553 (2019)]. Here, we estimated recovery of the discharge rate of IC neurons after forward maskers. We also quantified the impact of previous masker trials on IC rates by varying ISI. We recorded from the IC of awake rabbits using gaussian noise forward maskers and pure-tone probes. Interestingly, we observed significant effects of prior masking trials on discharge rates in response to the probe, even for ISIs larger than those typically used in psychophysical experiments. Our results show that ISIs of at least 1.5 s were required for full recovery of discharge rates after 70 dB SPL gaussian noise maskers. [NIH-NIDCD-010813.]