The effects of decreased audibility produced by high-pass noise masking on N1 and the mismatch negativity to speech sounds /ba/ and /da/
Journal/Book: J Speech Lang Hear Res. 1999; 42: 10801 Rockville Pike, Rockville, MD 20852-3279, USA. Amer Speech-Language-Hearing Assoc. 271-286.
Abstract: This study investigated the effects of decreased audibility produced by high-pass noise masking on the cortical event-related potentials (ERPs) N1 and mismatch negativity (MMN) to the speech sounds /ba/ and /da/, presented at 65 dB SPL. ERPs were recorded while normal listeners (N = 11) ignored the stimuli and read a book. Broadband masking noise was simultaneously presented at an intensity sufficient to mask the response to the speech sounds, and subsequently high-pass filtered. The conditions were QUIET (no noise); high-pass cutoff frequencies of 4000, 2000, 1000, 500, and 250 Hz; and broadband noise. Behavioral measures of discrimination of the speech sounds (d' and reaction time) were obtained separately from the ERPs for each listener and condition. As the cutoff frequency of the high-pass masker was lowered, ERP latencies increased and amplitudes decreased. The cutoff frequency where changes first occurred differed for N1 and MMN. N1 showed small systematic changes across frequency beginning with the 4000-Hz high-pass noise. MMN and behavioral measures showed large changes that occurred at approximately 1000 Hz. These results indicate that decreased audibility resulting from the masking, affects N1 and the MMN in a differential manner. N1 reflects the presence of audible stimulus energy, being present in all conditions where stimuli were audible, whether or not they were discriminable. The MMN is present only For those conditions where stimuli were behaviorally discriminable. These studies of cortical ERPs in high-pass noise studies provide insight into the changes in brain processes and behavioral performance that occur when audibility is reduced, as in hearing loss.
Note: Article Stapells DR, Univ British Columbia, Sch Audiol & Speech Sci, 5804 Fairview Ave, Vancouver, BC V6T 1Z3, CANADA
Keyword(s): event-related potentials; masking; mismatch negativity; behavioral; hearing loss; EVENT-RELATED POTENTIALS; HUMAN AUDITORY-CORTEX; COCHLEAR-IMPLANT; EVOKED-POTENTIALS; MEMORY TRACE; RESPONSES; DISCRIMINATION; PERCEPTION; STIMULUS; BRAIN