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J O Pickles

Publications and source records attributed to J O Pickles.

53 records · Page 3Linked to original sources
PubMed1984

Frequency threshold curves and simultaneous masking functions in high-threshold, broadly-tuned, fibres of the guinea pig auditory nerve.

Tuning curves for simultaneous masking were measured electrophysiologically, in single fibres of the auditory nerve. The recordings were made in guinea pigs with cochlear hearing losses. The masking paradigm was an analogy of that used in the determination of psychophysical tuning curves in man. Below the probe frequency, the slope of the masking function was similar to that of the frequency-threshold curve. Here, changes in the slope of the frequency-threshold curve with hearing loss were closely mirrored by changes in the slope of the masking function. Above the probe frequency, however, the masking function for low-threshold fibres had a shallower slope than the frequency-threshold curve. When the high-frequency slope of the frequency-threshold curve became shallower with hearing loss, the changes were not mirrored in the masking function, until the threshold was raised to 70-80 dB SPL. The results are discussed in terms of the influence of cochlear nonlinearity on frequency resolution, and the vulnerability of the nonlinearity.

Animals↗
PubMed1984

Cross-links between stereocilia in the guinea pig organ of Corti, and their possible relation to sensory transduction.

Hair cells of the guinea pig cochlea were preserved for electron microscopic examination by fixing in glutaraldehyde without the use of osmium. An extensive array of cross-links was seen between the stereocilia, by both scanning and transmission electron microscopy. The stereocilia were linked together laterally, particularly near their apical ends, by links running approximately at right angles to the long axis of the stereocilia. One set joined stereocilia of the same row, and another set joined stereocilia of the different rows, holding the tips of the shorter stereocilia in towards the longer stereocilia of the next row. In addition, the tip of each shorter stereocilium on the hair cell gave rise to a single, upwards-pointing link, which ran up to join the taller stereocilium of the next row. We suggest that distortion of this link would give rise to sensory transduction. On this basis, we are able to explain the V shape of the rows of stereocilia on outer hair cells. Within the rows, the three-dimensional arrangement of the stereocilia was different from that seen conventionally. Rather than standing parallel, the stereocilia of the different rows tapered in together at the tips, presumably held by the laterally-running cross-links. In addition, a membrane roughness, particularly pronounced in the region of the stereocilium which gives rise to the cross-links, was seen. However, the lateral and basal surface membranes of the hair cell, and the membranes of the internal organelles, had a more conventional appearance.

Animals↗
PubMed1984

Frequency threshold curves and simultaneous masking functions in single fibres of the guinea pig auditory nerve.

Tuning curves for simultaneous masking were measured electrophysiologically, in single fibres of the guinea pig auditory nerve. The masking paradigm used was an analogy of that used in the determination of psychophysical tuning curves in man. The resulting tuning curves ran nearly parallel to the corresponding neural frequency threshold curve, over all except the high-frequency portion of the tuning curve. There, the masking functions had a shallower slope than the excitatory frequency threshold curve. The frequency at which the slope became shallower had a close and consistent dependence on fibre characteristic frequency, reaching a value of 1.2 times fibre characteristic frequency in high-frequency fibres. Analysis of firing rates during the threshold determination gave information about the mechanism of the masking, and the results were supported by theoretical analysis. The results give information useful for the interpretation of psychophysical tuning curves, determined by simultaneous masking, in man.

Animals↗
PubMed1983

Auditory-nerve correlates of loudness summation with stimulus bandwidth, in normal and pathological cochleae.

The firing of guinea pig auditory nerve fibres was measured in response to bands of noise of many different bandwidths, centre frequencies and intensities. The total amount of activity in the auditory nerve fibre array was calculated as a function of the bandwidth and intensity of the stimulus. As the bandwidth of the stimulus increased, while its net intensity was kept constant, the total firing rate increased steadily. There was no sign of a breakpoint corresponding to the critical bandwidth, seen in psychophysical judgements of loudness with similar stimuli. Moreover, the slope of the relation between total activity and stimulus bandwidth was particularly shallow in fibres with shallow tuning curves. The results suggest that (i) while loudness may in broad terms be related to the total amount of activity in the auditory nerve, this is not true in detail, (ii) the critical bandwidth in loudness summation does not relate to the resolution bandwidth of the cochlea, and (iii) the slope of the psychophysical loudness summation function may be able to give information about the sharpness of neural tuning.

Acoustic Stimulation↗
PubMed1980

Is myosin in the cochlea a basis for active motility?

Recent evidence suggests that the stereocilia of cochlear hair cells contain actin filaments. The experiments reported here demonstrate the presence of myosin, suggesting that the mechanical properties of the hair cells may be actively modifiable by actin-myosin interactions as in muscle cells.

Actins↗
PubMed1980

Responses of auditory nerve fibres in the guinea pig to noise bands of different widths.

The responses of single fibres of the auditory nerve were recorded in anaesthetised guinea pigs. The fibres were stimulated by bandpass noise centered on the characteristic frequency. As the noise bandwidth was increased at constant spectral density, the firing rate increased, came to a peak, and in the majority of fibres, declined at wider bandwidths. The bandwidth at which the firing was at a peak had a mean value of 34% of the characteristic frequency. On average, the evoked firing rate was supressed by 8% at the widest bands of noise used. However, 17% of fibres showed no suppression at all. In those that did, suppression was still visible if the stimulus intensity was so high as to drive the firing into saturation.

Acoustic Stimulation↗
PubMed1979

Psychophysical frequency resolution in the cat as determined by simultaneous masking and its relation to auditory-nerve resolution.

Critical bandwidths were measured behaviorally at 1 and 2 kHz by simultaneous masking in four cats. Three methods were used. They were (i) the masking of a tone by noise of variable bandwidth, (ii) the masking of a narrow-band signal by two tones, and (iii) the masking of a tone by noise of rippled spectrum. The three methods agreed closely and gave a mean critical bandwidth of 410 Hz at 1 kHz and 690 Hz at 2 kHz. These values were about three times as great as the electrophysiologically-determined effective bandwidths of single fibers of the auditory nerve at the same frequencies, both as measured in other animals, and in one of the animals that had been tested behaviorally as well. Psychophysical tuning curves were also determined behaviorally; in contrast, they agreed closely with auditory-nerve fibers in both bandwidth and slope. The results suggest that the critical band as measured by simultaneous masking is not a close relation of the frequency-threshold curve of auditory-nerve fibers, but that the psychophysical tuning curve possibly may be. Possible reasons and implications are discussed.

Animals↗
PubMed1976

Role of centrifugal pathways to cochlear nucleus in determination of critical bandwidth.

Atropine sulfate was applied locally to the cochlear nucleus of three unanesthetized cats in order to block the cholinergic centrifugal innervation of the nucleus. The critical bandwidth was measured behaviorally from the masked thresholds of 1-kHz tone pips in different bandwidths of masking noise. Atropine increased the critical bandwidth markedly. This suggests that normally the centrifugal pathways influence the critical bandwidth. Saline solutions alone had no effect, and if the cannula was not accurately implanted over the cochlear nucleus, atropine had no effect either.

Acoustic Stimulation↗
PubMedDate not supplied

Normal critical bands in the cat.

Critical bands in the cat were measured by a behavioural psychophysical method. Pure tones were masked by noise by variable bandwidth but constant total power, geometrically centred on the test tone; the point at which the masked threshold began to fall as the masker bandwidth was increased estimated the critical bandwidth. At 2 kHz the critical bandwidth was also measured from the wideband masked thresholds of both tones and noise of variable bandwidth: this produced the same result as the first method. The measured critical bandwidth was greater than previously published values of the effective bandwidths of single fibres of the auditory nerve. The results do not fit in with the commonly accepted theory that the critical band represents the resolution of the cochlea.

Acoustic Stimulation↗
PubMedDate not supplied

An investigation of sympathetic effects on hearing.

Absolute and masked thresholds were measured behaviourally in the cat before and after lesion of the superior cervical ganglion and sympathetic trunk. No changes were found, even though testing was continued for up to 2 1/2 years afterwards. However in acute experiments in the anaesthetised animal small increases in the neural N1 potential of the cochlea, without any effect on the microphonic, were found after stimulation of the sympathetic trunk.

Action Potentials↗