AP tuning curves from normal and pathological human and guinea pig cochleas

Abstract

Measures of cochlear selectivity can be obtained from compound responses using tone-on-tone masking procedures [Dallos and Cheatham, J. Acoust. Soc. Am. 59, 591--597 (1976)]. For the normal guinea pig, cochlear fiber tuning is sharper by a factor of 1.8 than AP tuning curves using simultaneous masking (threshold criterion = 25% N1 amplitude reduction). Anesthesia does not appear to affect AP tuning. In pathological cochleas, AP tuning is broadened by a factor of 2--3, and differences between forward and simultaneous masking curves are reduced. Tuning changes can sometimes occur without threshold elevation. AP tuning curves were obtained from humans during transtympanic electrocochleography. For subjects with near normal thresholds, Q10dB values (simultaneous masking) are approximately 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Using the relationship between cochlear fiber tuning and AP tuning in the guinea pig, estimates of human cochlear fiber tuning are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz. Patients with threshold elevations of more than 30 dB resulting from cochlear deafness have AP tuning curves less sharply tuned by a factor of 2--3.

Unexceptional sharpness of frequency tuning in the human cochlea

“…3-10). That conclusion coincides with an earlier study, based on the measurement of compound action potential tuning curves (APTCs) (11), but is at odds with an investigation that measured frequency selectivity in humans and chinchillas using the same psychophysical task (12).…”

“…3) reported similar Q 10 values for probe tones between 2 and 8 kHz (11,41). A third study, by Rutten (42) pig (dashed line) by using manual control of stimulus frequency and intensity and audiovisual threshold detection are larger and increasingly depart with increasing frequency from those of a more recent study (43) (solid line), which used an automated procedure (e.g., ref.…”

“…Therefore, to the extent that systematic quantitative relationships exist between the Q 10 values of ANFTCs and APTCs in experimental animals, it should be possible to predict the Q 10 values of human ANFTCs. Three studies (11,41,42) have used SM procedures to measure APTCs in humans. Their results are summarized in Fig.…”

Reduction in Sharpness of Frequency Tuning but not Endocochlear Potential in Aging and Noise-Exposed BALB/cJ Mice

“…Surprisingly few data have been published describing frequency tuning in mice or showing how genetic defects impact the relationship between the condition of the sensory epithelium and frequency tuning. CAPTC shapes are assumed to be representative of frequency tuning curves of auditory nerve ®bers under both normal and abnormal conditions (Harrison et al 1981). Tuning curves in sensitive mouse cochleas showed the classic tip±tail con®guration of single auditory neurons in mammals (Kiang et al 1965;Evans 1972;Geisler et al 1974;Schmiedt et al 1980;Salvi et al 1982) and were similar to CAP tuning curves derived in other species (Dallos and Cheatham 1976;Harris 1979;Harrison et al 1981;Dolan et al 1985;Brown and Abbas 1987), as well as ABR masking curves in mice (Saunders and Gar®nkle 1983;Henry 1985;Henry et al 1992;Walsh and McGee 2001).…”

Neural representation of spectral and temporal information in speech

“…Evans 1992), whereas others have not (e.g. Pickles 1979;Harrison et al 1981). Thus, while most studies have found behavioural filters to be wider in animals than in human subjects, it is not clear how that result should be interpreted in terms of the relative widths of AN tuning curves .…”