Tonotopic Selectivity in Cats and Humans: Electrophysiology and Psychophysics

Abstract

We describe a scalp-recorded measure of tonotopic selectivity, the “cortical onset response” (COR) and compare the results between humans and cats. The COR results, in turn, were compared with psychophysical masked-detection thresholds obtained using similar stimuli and obtained from both species. The COR consisted of averaged responses elicited by 50-ms tone-burst probes presented at 1-s intervals against a continuous noise masker. The noise masker had a bandwidth of 1 or 1/8th octave, geometrically centred on 4000 Hz for humans and on 8000 Hz for cats. The probe frequency was either − 0.5, − 0.25, 0, 0.25 or 0.5 octaves re the masker centre frequency. The COR was larger for probe frequencies more distant from the centre frequency of the masker, and this effect was greater for the 1/8th-octave than for the 1-octave masker. This pattern broadly reflected the masked excitation patterns obtained psychophysically with similar stimuli in both species. However, the positive signal-to-noise ratio used to obtain reliable COR measures meant that some aspects of the data differed from those obtained psychophysically, in a way that could be partly explained by the upward spread of the probe’s excitation pattern. Our psychophysical measurements also showed that the auditory filter width obtained at 8000 Hz using notched-noise maskers was slightly wider in cat than previous measures from humans. We argue that although conclusions from COR measures differ in some ways from conclusions based on psychophysics, the COR measures provide an objective, noninvasive, valid measure of tonotopic selectivity that does not require training and that may be applied to acoustic and cochlear-implant experiments in humans and laboratory animals.

Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings

“…A receiver-operating characteristic (ROC) analysis was used to determine the significance of the ACC magnitudes for individual cats (Green and Swets 1966;Macmillan and Creelman 2005). The ROC is derived from the distributions of trial-sampled magnitudes of the ACC and the estimated background noise.…”

High Spectral and Temporal Acuity in Primary Auditory Cortex of Awake Cats

“…In contrast to that trend, we note that human listeners show more acute frequency discrimination at moderate-to-high sensation levels than at lower levels (e.g., [ 37 ]). As a point of reference, we recently estimated the Equivalent Rectangular Bandwidth of the cat’s auditory filter using a psychophysical notched-noise procedure [ 38 ]: the value of the filter centered at 8 kHz was 0.2 oct. Of the 78 units in our sample having BFs within an octave of 8 kHz, only 14 (18%) had bandwidths ≤ 0.2 oct, and all those units had best levels ≤ 20 dB SPL.…”

Exploring the Use of Interleaved Stimuli to Measure Cochlear-Implant Excitation Patterns

“…To our knowledge, this study is the first to investigate pTP excitation patterns in humans with interleaved masking. We have argued that interleaved stimulation allows for an easier comparison with electrophysiological recordings in humans and animals than forward-masking, because one can elicit cortical onset responses without contamination by an offset response to the masker, as would occur in a forward-masking paradigm [ 6 ].…”

“…Mens and Berenstein [ 30 ] used a ‘flat TP + 2’ configuration, in which, for example, current injected via electrode 4 would be returned equally from electrodes 1, 2, 6, and 7, and reported no benefit over monopolar stimulation for speech recognition. As discussed in Guérit et al [ 6 ], increasing the spacing between stimulating electrodes in tripolar stimulation may have the benefit of sharpening neural excitation patterns, but may also have a trade-off between how much current is returned through the side electrodes. Widening the tripolar configuration while injecting substantial amounts of current at the side electrodes might create side-lobes of excitation, in the same way as wide bipolar stimulation creates bimodal peaks of neural excitation [ 31 , 32 ].…”

“…As a first step towards resolving the discrepancy between the human and animal results, we developed a non-invasive electrophysiological method for measuring masked excitation patterns in NH humans and cats, which was validated against psychophysical measures in the two species [ 6 ]. That paradigm involved scalp-based recordings of the cortical onset response to tones of different frequencies presented against a continuous noise masker.…”