Factors affecting psychophysical tuning curves for hearing-impaired subjects with high-frequency dead regions.
A dead region (DR) is a region of the cochlea where there are no functioning inner hair cells and/or neurons. DRs can be detected using the threshold-equalizing-noise (TEN) test, but psychophysical tuning curves (PTCs) are sometimes used to give a more precise estimate of the edge frequency of a DR; a shifted tip of the PTC indicates a DR. We show here that the shapes of PTCs for hearing-impaired subjects can be influenced by the detection of beats and simple difference tones (SDTs). As a result, PTCs can have tips at f(s), even when f(s) falls in a DR. PTCs were measured for subjects with mild to moderate low-frequency and severe high-frequency hearing loss using sinusoidal and narrowband noise maskers (80-, 160-, 320-Hz wide): (1) in quiet; (2) in the presence of additional lowpass filtered noise (LF noise) designed to mask SDTs; (3) in the presence of a pair of low-frequency tones designed to interfere with the detection of beats (MDI tones). In condition (1), the PTCs were often W-shaped, with a sharp tip at f(s). This occurred less for the wider noise bandwidths. For subjects with good low-frequency hearing, the LF noise often reduced or eliminated the tip at f(s), suggesting that this tip was partly caused by detection of SDTs. For the sinusoidal and 80-Hz wide noise maskers, the addition of the MDI tones reduced the masker level required for threshold for masker frequencies adjacent to f(s), for nearly all subjects, suggesting a strong influence of beat detection. To minimize the influence of beats, we recommend using noise maskers with a bandwidth of 160 or (preferably) 320 Hz. In cases of near-normal hearing at low frequencies, we recommend using an additional LF noise to mask SDTs.
Kluk
Karolina
K
Department of Experimental Psychology, University of Cambridge, Cambridge CB2 3EB, UK. kk278@cam.ac.uk
Moore
Brian C J
BC
D000161:Acoustic Stimulation; D000368:Aged; D000369:Aged, 80 and over; D001299:Audiometry / Q000379:methods; D003051:Cochlea / Q000473:pathology / Q000503:physiopathology; D006316:Hearing Loss, High-Frequency / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010470:Perceptual Masking / Q000502:physiology; D011571:Psychoacoustics