Auditory Forward Masking Explained by a Subcortical Model with Efferent Control of Cochlear Gain

Abstract

AbstractPrevious physiological and psychophysical studies have explored whether feedback to the cochlea from the efferent system influences forward masking. The present work proposes that the limited growth-of-masking (GOM) observed in auditory-nerve (AN) fibers may have been misunderstood; namely, that this limitation may be due to the influence of anesthesia on the efferent system. Building on the premise that the unanesthetized AN may exhibit GOM similar to more central nuclei, the present computational modeling study demonstrates that feedback from the medial olivocochlear (MOC) efferents may account for GOM observed physiologically in onset-type neurons in both the cochlear nucleus and inferior colliculus (IC), as well as in human psychophysics. Additionally, the computational model of MOC efferents used here generates a decrease in masking with longer masker-signal delays similar to that observed in IC physiology and in psychophysical studies. An advantage of this explanation over alternative physiological explanations (e.g., that forward masking requires inhibition from the superior paraolivary nucleus) is that this theory can explain forward masking observed in the brainstem, early in the ascending pathway. For explaining psychoacoustic results, one strength of this model is that it can account for the lack of elevation in thresholds observed when masker level is randomly varied from interval-to-interval, a result that is difficult to explain using the conventional temporal-window model of psychophysical forward masking.Significance StatementThe simulations presented here demonstrate that a recent computational model of the auditory subcortex including medial-olivocochlear efferents generates forward masking, an increase in detection threshold for a short probe tone following a preceding sound. This model explains results from both physiological recordings and psychoacoustic experiments. The theory that efferent control of cochlear gain is a contributing mechanism for forward masking has several advantages. This theory can explain masking exhibited by brainstem neurons, a phenomenon not explained by current physiological theories in which forward-masking originates later in the ascending pathway. Additionally, this theory explains results for a psychoacoustic task with random variation in masker level, results not explained by the theory that persistent masker energy interferes with detection of the probe.