Effects of fast, slow, and adaptive amplitude compression on children's and adults' perception of meaningful acoustic information.

Abstract

Fast- and slow-acting amplitude compression parameters have complementary strengths and weaknesses that limit the full benefit of this feature to hearing aid users. Adaptive time constants have been suggested in the literature as a means of optimizing the benefits of amplitude compression. The purpose of this study was to compare the effects of three amplitude compression release times (slow, fast, and adaptive) on children's and adults' accuracy for categorizing speech and environmental sounds. Participants were asked to categorize speech or environmental sounds embedded in short trials containing low-level playground noise. Stimulus trials included either a high-level environmental sound followed by a lower-level speech stimulus (word) or a high-level speech stimulus followed by a lower-level environmental sound. The listeners responded to the second (low-level) stimulus in each trial. The two stimuli overlapped temporally in half of the trials but not in the other half. The stimulus trials were processed to simulate amplitude compression having fast (40 msec), slow (800 msec), or adaptive release times. The adaptive-compression parameters operated in a slow fashion until a sudden increase/decrease in level required a rapid change in gain. Participants were 15 children and 26 adults with hearing loss (HL) as well as 20 children and 21 adults with normal hearing (NH). DATA COLLECTION AND ANALYSES: Performance (in % correct) was arcsine transformed and subjected to repeated-measures analysis of variance with pairwise comparisons of significant main effects using Bonferroni adjustments for multiple comparisons. Overall, the performance of listeners with HL was poorer than that of the listeners with NH and performance for the environmental sounds was poorer than for the speech stimuli, particularly for the adults and children with HL. Significant effects of age group, stimulus overlap, and compression speed were observed for the listeners with NH, whereas effects of stimulus overlap and compression speed were found for the listeners with HL. Whereas listeners with NH achieved optimal performance with slow-acting compression, the listeners with HL achieved optimal performance with adaptive compression. Although slow, fast, and adaptive compression affects the acoustic signal in a subtle fashion, amplitude compression significantly affects perception of speech and environmental sounds.