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PubMed1981

A psychophysical investigation of auditory functioning in schizophrenia.

The present report is of the application of Treisman's (1964) model of perceptual functioning to the study of schizophrenic hallucinations. It was hypothesized that hallucinators would perform on an auditory threshold task as if possessing a perceptual system showing high levels of spontaneous neural activity (In). Three groups were compared on the Weber functions for pure tone intensity: schizophrenic hallucinators, old people and anxiety neurotics. From these functions, estimates of In were calculated using Barlow's (1957b) method. No group differences were found. An alternative explanation of schizophrenic hallucinations, in terms of increased responsiveness to normal levels of background sensory activity, is proposed.

Adult↗
PubMed1977

Direct excitatory interactions between spinal motoneurones of the cat.

1. Ninety-seven spinal motoneurones were identified by their antidromic invasion following stimulation of the muscle nerve and submitted to a series of four tests to reveal a possible direct excitation between motoneurones. 2. Threshold differentiation, refractoriness, hyperpolarization and collision revealed antidromically induced depolarizations in fourteen of the ninety-seven tested motoneurones. 3. The parameters of the antidromically induced depolarizations indicate a short latency, a low amplitude and independence with regard to the membrane polarization. 4. It is concluded that the antidromically induced depolarizations reached the impaled motoneurone via a route other than its own axon. 5. The mechanism may involve either electrotonic interactions between neighbouring motoneurones or excitatory recurrent collaterals between synergist motoneurones.

Action Potentials↗
PubMed2004

Sequential streaming and effective level differences due to phase-spectrum manipulations.

Roberts et al. [J. Acoust. Soc. Am. 112, 2074-2085 (2002)] demonstrated that sequential stream segregation occurs with stimuli that differ only in phase spectrum. We investigated if this was partly due to differences in effective excitation level. Stimuli were harmonic complexes with a 100 Hz fundamental, 1250-2500 Hz passband, and cosine, alternating, or random component phase. In experiment 1, the complex tones were used as forward maskers of 20-ms probe tones at 1000, 1250, 1650, 2050, 2500, and 3000 Hz. While there was no significant difference in the masking produced by the cosine- and alternating-phase stimuli, the random-phase stimulus produced significantly greater masking, equivalent to a difference in overall effective excitation level of 12.6 dB. Experiments 2 and 3 used the asynchrony detection and subjective streaming tasks of Roberts et al. Successive stimuli had identical phase, but differed in level by 0, 1, 3, 5, 10, or 15 dB. Stream segregation increased once the level difference reached 5 dB. While some of the stream segregation observed by Roberts et al. may have been due to a difference in effective excitation level, this does not account for the stream segregation between cosine- and alternating-phase stimuli.

Acoustic Stimulation↗
PubMed2004

The effects of real and illusory glides on pure-tone frequency discrimination.

Experiment 1 measured pure-tone frequency difference limens (DLs) at 1 and 4 kHz. The stimuli had two steady-state portions, which differed in frequency for the target. These portions were separated by a middle section of varying length, which consisted of a silent gap, a frequency glide, or a noise burst (conditions: gap, glide, and noise, respectively). The noise burst created an illusion of the tone continuing through the gap. In the first condition, the stimuli had an overall duration of 500 ms. In the second condition, stimuli had a fixed 50-ms middle section, and the overall duration was varied. DLs were lower for the glide than for the gap condition, consistent with the idea that the auditory system contains a mechanism specific for the detection of dynamic changes. DLs were generally lower for the noise than for the gap condition, suggesting that this mechanism extracts information from an illusory glide. In a second experiment, pure-tone frequency direction-discrimination thresholds were measured using similar stimuli as for the first experiment. For this task, the type of the middle section hardly affected the thresholds, suggesting that the frequency-change detection mechanism does not facilitate the identification of the direction of frequency changes.

Acoustic Stimulation↗
PubMed2004

Sequential F0 comparisons between resolved and unresolved harmonics: no evidence for translation noise between two pitch mechanisms.

Carlyon and Shackleton [J. Acoust. Soc. Am. 95, 3541-3554 (1994)] suggested that fundamental-frequency (F0) discrimination performance between resolved and unresolved harmonics is limited by an internal "translation" noise between the outputs of two distinct F0 encoding mechanisms, in addition to the encoding noise associated with each mechanism. To test this hypothesis further, F0 difference limens (DLF0s) were measured in six normal-hearing listeners using sequentially presented groups of harmonics. The two groups of harmonics presented on each trial were bandpass filtered into the same or different spectral regions, in such a way that both groups contained mainly resolved harmonics, both groups contained only unresolved harmonics, or one group contained mainly resolved and the other only unresolved harmonics. Three spectral regions (low: 600-1150 Hz, mid: 1400-2500 Hz, or high: 3000-5250 Hz) and two nominal F0s (100 and 200 Hz) were used. The DLF0s measured in across-region conditions were well accounted for by a model assuming only two sources of internal noise: the encoding noise estimated on the basis of the within-region results plus a constant noise associated with F0 comparisons across different spectral regions, independent of resolvability. No evidence for an across-pitch-mechanism translation noise was found. A reexamination of previous evidence for the existence of such noise suggests that the present negative outcome is unlikely to be explained by insufficient measurement sensitivity or an unusually large across-region comparison noise in the present study. While the results do not rule out the possibility of two separate pitch mechanisms, they indicate that the F0s of sequentially presented resolved and unresolved harmonics can be compared internally at no or negligible extra cost.

Acoustic Stimulation↗
PubMed2005

Binaural release from informational masking in a speech identification task.

Binaural release from informational masking (IM) was examined in a speech identification task. Target and masker sentences were processed into mutually exclusive frequency bands, thus limiting energetic masking (EM), and presented over headphones. In a baseline condition, both were presented monotically to the same ear (TmMm). Despite minimal frequency overlap between target and masker, the presence of the masker resulted in reduced performance, or IM. Presenting the target monotically and the masker diotically (TmMo) resulted in a release from IM. Release was also obtained by imposing interaural differences in level (ILDs) and in time (ITDs) on the maskers (T(m)M(ILD), T(m)M(ITD)). Any masker with a perceived lateral position that differed from that of a truly monaural stimulus resulted in a similar amount of release from IM relative to TmMm. For binaural targets and maskers (T(o)M(ILD), T(o)M(ITD)), release was seen whenever ITDs or ILDs differed between target and masker. These results suggest that binaural cues can be very effective in reducing IM. Because mechanisms based on differences in perceived location make predictions that are similar to those of nonlocation-based binaural mechanisms, a variant of the equalization-cancellation model is also considered.

Acoustic Stimulation↗
PubMed2006

Discrimination of nonlinear frequency glides.

Discrimination thresholds for short duration nonlinear tone glides that differed in glide rate were measured in order to determine whether cues related to rate of frequency change alone were sufficient for discrimination. Thresholds for rising and falling nonlinear glides of 50-ms and 400-ms duration, spanning three frequency excursions (0.5, 1, and 2 ERBs) at three center frequencies (0.5, 2.0, and 6.0 kHz) were measured. Results showed that glide discrimination was possible when duration and initial and final frequencies were identical. Thresholds were of a different order to those found in previous studies using linear frequency glides where endpoint frequency or duration information is available as added cues. The pattern of results was suggestive of a mechanism sensitive to spectral changes in time. Thresholds increased as the rate of transition span increased, particularly above spans of 1 ERB. The Weber fraction associated with these changes was 0.6-0.7. Overall, the results were consistent with an excitation pattern model of nonlinear glide detection that has difficulty in tracking signals with rapid frequency changes that exceed the width of an auditory filter and are of short duration.

Acoustic Stimulation↗
PubMed2006

Effect of adaptive psychophysical procedure on loudness matches.

Large variability in equal-loudness matches has been observed across studies. The purpose of the present study was to gain insight into the extent to which this variability results from differences in psychophysical procedures and/or differences among listeners. Four adaptive two-interval, two-alternatives-forced-choice procedures were used to obtain equal-loudness matches between 5- and 200-ms 1-kHz tones as a function of level for each of six normal listeners. The procedures differed primarily in the sequence in which the stimuli were presented. The variations tested were the ordering of stimuli by amplitude across blocks of trials (both increasing and decreasing amplitudes), randomizing the order across those blocks, and randomizing the order within blocks. The random-within-block procedure, which sought to randomize any intertrial information, yielded a significantly greater amount of temporal integration than the other three procedures. The results show significant differences in temporal integration measurements at moderate levels for the same listeners across different procedures. Therefore, although there are individual differences among listeners in the amount of temporal integration measured across paradigms, the choice of paradigm also affects the amount of temporal integration measured at moderate levels.

Acoustic Stimulation↗
PubMed1978

Theory of binaural interaction based on auditory-nerve data. III. Joint dependence on interaural time and amplitude differences in discrimination and detection.

This paper is primarily concerned with issues of symmetry-asymmetry in the joint dependence of binaural performance on interaural time delay and interaural amplitude ratio. The predictions of our model based on auditory-nerve data are shown to be inadequate for available data showing asymmetries in interaural time discrimination. Measured detection thresholds for a 500-Hz tone burst masked by wide-band noise are reported for nonunity amplitude ratios and both polarities of delays in order to test for asymmetries analogous to those observed in the time discrimination case. The detection results show only small asymmetries and are not inconsistent with the model. A general discussion of our model and the implications of available empirical results leads to a suggested modification of the model. We show by an example that modifications of the type we are suggesting are capable of describing the detection data and at least the gross trends of the discrimination data.

Auditory Perception↗
PubMed1978

Phase locking in monaural and binaural medullary neurons: implications for binaural phenomena.

The synchrony of neural impulses in response to low-frequency sinusoids is described for auditory medullary neurons. The results are summarized as follows: (1) In general, neural synchrony is found to improve with increases in intensity and frequency of stimulation for both monaural and binaural neurons when measurements are make in absolute time. (2) An analysis of our population of neurons implies that two separate mechanisms are responsible for the decrease in synchrony found in many neurons as compared to primarylike neurons with high-locking ability. The two mechanisms are convergence of mistimed impulses and electrontonic changes which occur in dendrites. (3) An analysis of binaural vector strength data provides an explanation for physiological differences between cyclic and noncyclic vector strengths as a function of interaural time and reveals the effects of mistimed convergence upon neural synchrony.(4) In contrast to the inferior colliculus, where the neurons discharge best with contralateral leads in time, superior olivary neurons exhibited no such preference. Some discharge best to ipsilateral while others to contralateral leads. This comparison reveals a striking difference in the coding characteristics of medullary and inferior colliculus neurons. (5) Finally, the results are compared with the psychophysically determined difference limens.

Action Potentials↗