Abstract
A target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This phenomenon, known as auditory enhancement, reflects a general principle of contrast enhancement, and may help in the detection of new acoustic events in the environment and in establishing the perceptual constancy of speech and other biologically relevant sounds under varying acoustic conditions. Surprisingly, no neural correlates of this important phenomenon have been reported in humans. Here we used the auditory steady state response (ASSR) to determine whether the neural response to the target is amplified under conditions of enhancement. We used a double-modulation paradigm, involving the simultaneous amplitude modulation of a tone with two modulation frequencies, to distinguish cortical from subcortical contributions to this phenomenon. Robust phase-locked neural responses to both the target and masker were identified at both cortical and subcortical levels. Consistent with perceptual results, the response to the target tone embedded in the simultaneous maskers increased in the presence of the precursor, whereas the response to the masker components remained constant across conditions. The quantitative pattern of results suggest that the enhancement effects emerge at a subcortical level but are further enhanced within the auditory cortex.
Footnotes
fengl{at}umn.edu, mehta{at}umn.edu, oxenham{at}umn.edu