Effects of Aging, Continuity and Frequency Difference on the Time Course of Auditory Perceptual Organization
Raynor, Graham Komei
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Effective everyday hearing requires the auditory system to organize auditory input into perceptual streams corresponding to objects of interest. Changes in this process may be responsible for age-related deterioration in the capacity to effectively hear important sounds masked by background noise. Younger (18-25) and older (55+) adults with healthy hearing listened to 10-second intervals of a simple pattern of “ABA” tone triplets. The ABA patterns are used as a model of real-world auditory streaming, because they are initially perceived as one integrated stream, and over time are reorganized into two segregated streams. Participants performed a target-detection task designed to index their perceptual organization of the tones, which does not depend on potentially-biased, subjective judgment (Thompson, Carlyon, & Cusack, 2011). Complex tones with narrowly-spaced, unresolvable frequency components were used in this experiment to control for age-related decreases in frequency selectivity. Both groups demonstrated a capacity for segregating the A and B tones based on differences in harmonic spacing, as predicted. However, despite our acoustic controls the older adults showed significantly less segregation of the 6ST stimuli, indicating that there are additional age-related changes in auditory streaming, which make them less likely to segregate in response to harmonic spacing differences. Additionally, older adults showed significantly better overall performance on the task than younger adults, indicating that the age differences are not simply due to age-related deficits in task execution. The ABA intervals were presented either continuously, or with 5-second interruptions prior to each trial that have previously been shown to “reset” perceptual streaming back to an integrated percept (Cusack, Deeks, Aikman, & Carlyon, 2004). For both age groups interruptions preceding the ABA intervals were shown to be capable of resulting in decreased segregation, as predicted. Targets were presented at 4 time points (2, 4, 6, and 8 seconds) in order to test for age differences in the time course of streaming. In the results for the 8-semitone stimuli, we observed strong evidence for delayed build-up in older adults, in response to the Gap condition. However, this evidence was not statistically conclusive and future experiments are needed determine the effect’s validity.