New perspectives on the measurement and time course of auditory enhancement.

Abstract

A target sound can become more audible and may ‘pop out’\nfrom a simultaneously presented masker if the masker is presented first by\nitself, as a precursor. This phenomenon, known as auditory enhancement, may\nreflect the general perceptual principle of contrast enhancement, which\nfacilitates adaptation to ongoing acoustic conditions and the detection of new\nevents. Little is known about the mechanisms underlying enhancement, and\npotential confounding factors have made the size of the effect and its time\ncourse a point of contention. Here we measured enhancement as a function of\nprecursor duration and delay between precursor offset and target onset, using\ntwo single-interval pitch comparison tasks, which involve either same-different\nor up-down judgments, to avoid the potential confounds of earlier studies.\nAlthough these two tasks elicit different levels of performance and may reflect\ndifferent underlying mechanisms, they produced similar amounts of enhancement.\nThe effect decreased with decreasing precursor duration, but remained present\nfor precursors as short as 62.5 milliseconds, and decreased with increasing gap\nbetween the precursor and target, but remained measurable 1 second after the\nprecursor. Additional conditions, examining the effect of precursor/masker\nsimilarity and the possible role of grouping and cueing, suggest multiple\nsources of auditory enhancement.