Masking of auditory brainstem responses in young and aged gerbils.
Auditory brainstem responses (ABR) were recorded in the presence of low-pass (1 kHz cutoff) or high-pass (8 kHz cutoff) filtered noise in young (4-8 month) and aged (36 month) gerbils. For low-pass maskers, aged gerbils had higher masked thresholds at 2 and 4 kHz than young subjects. This was true for all aged subjects, including those with quiet thresholds similar to those of young controls. For high-pass masking, the majority of aged subjects had higher masked thresholds at 2 and 4 kHz than young controls; however, aged subjects with relatively normal quiet thresholds had masked thresholds similar to those of young subjects. A modified power-law (MPL) model was used to predict masked thresholds for aged subjects. Thresholds measured in the presence of low-pass noise were higher than predicted in many of the aged subjects, particularly those with near-normal quiet thresholds. In contrast, thresholds measured in the presence of the high-pass masker were similar to the predicted thresholds. These results suggest that: (a) excess masking occurred in aged subjects for low-pass, but not high-pass, maskers; (b) the excess masking occurred independently of quiet thresholds; and (c) excess upward spread of masking was related to the spectrum of the masker and not the 2 and 4 kHz regions of the auditory periphery.
Boettcher
F A
FA
Department of Otorhinolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425-2242, USA.
Mills
J H
JH
Dubno
J R
JR
Schmiedt
R A
RA
D000161:Acoustic Stimulation; D000375:Aging / Q000502:physiology* / Q000523:psychology; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005849:Gerbillinae; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology; D006801:Humans; D008954:Models, Biological; D009622:Noise; D010470:Perceptual Masking / Q000502:physiology; D011571:Psychoacoustics