Psychophysical suppression effects for tonal and speech signals

This experiment assessed the benefits of suppression and the impact of redu ced or absent suppression on speech recognition in noise. Psychophysical su ppression was measured in forward masking using tonal maskers and suppresso rs and band limited noise maskers and suppressors. Subjects were 10 younger and 10 older adults with normal hearing, and 10 older adults with cochlear hearing loss. For younger subjects with normal hearing, suppression measur ed with noise maskers increased with masker level and was larger at 2.0 kHz than at 0.8 kHz. Less suppression was observed for older than younger subj ects with normal hearing. There was little evidence of suppression for olde r subjects with cochlear hearing loss. Suppression measured with noise mask ers and suppressors was larger in magnitude and more prevalent than suppres sion measured with tonal maskers and suppressors. The benefit of suppressio n to speech recognition in noise was assessed by obtaining scores for filte red consonant-vowel syllables as a function of the bandwidth of a forward m asker. Speech-recognition scores in forward maskers should be higher than t hose in simultaneous maskers given that forward maskers are less effective than simultaneous maskers. If suppression also mitigated the effects of the forward masker and resulted in an improved signal-to-noise ratio, scores s hould decrease less in forward masking as forward-masker bandwidth increase d, and differences between scores in forward and simultaneous maskers shoul d increase, as was observed for younger subjects with normal hearing. Less or no benefit of suppression to speech recognition in noise was observed fo r older subjects with normal hearing or hearing loss. In general, as suppre ssion measured with tonal signals increased, the combined benefit of forwar d masking and suppression to speech recognition in noise also increased. (C ) 2001 Acoustical Society of America.