Constantine Trahiotis

Lateralization of complex binaural stimuli: A weighted‐image model

This article describes a new model that predicts the subjective lateral position of bandpass stimuli. It is assumed, as in other models, that stimuli are bandpass filtered and rectified, and that the rectified outputs of filters with matching center frequencies undergo interaural cross correlation. The model specifies and utilizes the shape and location of assumed patterns of neural activity that describe the cross-correlation function. Individual modes of this function receive greater weighting if they are straighter (describing consistent interaural delay over frequency) and/or more central (describing interaural delays of smaller magnitude). This weighting of straightness and centrality is used by the model to predict the perceived laterality of several types of low-frequency bandpass stimuli with interaural time delays and/or phase shifts, including bandpass noise, amplitude-modulated stimuli with time-delayed envelopes, and bandpass-filtered clicks. This model is compared to other theories that describe lateralization in terms of the relative contributions of information in the envelopes and fine structures of binaural stimuli.

Behavioral Investigation of Some Possible Effects of Sectioning the Crossed Olivocochlear Bundle

Due to the paucity of behavioral data bearing on the possible role of the efferent auditory system, an investigation of some possible functions of the crossed olivocochlear bundle (OCB) has been undertaken, using cats. Behavioral correlates of transection of the crossed OCB were sought in such measures as absolute thresholds in quiet, effective masking over differing noise levels and frequencies, and temporary threshold shifts. The following results were obtained after transection of crossed OCB: (1) Absolute thresholds were unchanged; (2) amount of masking at 1000 Hz and 2000 Hz increased (though the shift was not statistically significant with the small number of subjects tested); and (3) TTS did not differ greatly for the transected animals.

Peripheral auditory processing and investigations of the “precedence effect” which utilize successive transient stimuli

This article addresses how a consideration of peripheral auditory processing can help to understand experiments concerning binaural precedence that employ successive binaural transients. It appears that much of the patterning of the behavioral data is amenable to an explanation based on peripheral interactions that result from auditory filtering and the functioning of auditory hair cells in combination with a binaural model based on cross correlation. A noteworthy aspect of this approach is that it does not include inhibitory mechanisms like those commonly invoked to explain binaural precedence.

Interaural correlation discrimination: II. Relation to binaural unmasking

Many theoretical models of binaural interaction assume that sensitivity to interaural correlation underlies binaural unmasking. This paper explores the extent to which sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation implied by results from binaural detection experiments are consistent with sensitivity to changes in interaural correlation measured directly in correlation discrimination experiments. The vehicle for this exploration is a simplified model of the underlying processes assumed by many models of binaural unmasking for the detection of narrow-band signals in the presence of broadband noise. Consideration is given to psychometric function slopes, detection thresholds, bandwidth effects, duration effects, level effects, and interaural-parameter effects. Although many of the results obtained from our analysis are consistent with the notion that the cue in binaural detection tasks is a change in interaural correlation, some significant inconsistencies are noted.

Lateralization of bands of noise: Effects of bandwidth and differences of interaural time and phase

The effects of stimulus bandwidth on lateralization of narrow bands of noise were investigated with an acoustic pointing task. Stimuli were narrow bands of noise (centered on 500 Hz with bandwidths ranging from 50-400 Hz) that contained interaural time delays and/or interaural phase shifts. The overall extent of lateralization and sidedness was found to vary greatly as a function of stimulus bandwidth, as insightfully discussed earlier by Jeffress [L. A. Jeffress, Foundations of Modern Auditory Theory, edited by J. V. Tobias (Academic, New York, 1972)]. The data are qualitatively consistent with a weighted-image model [Stern et al., J. Acoust. Soc. Am. 84, 156-165 (1988)] that specifies and utilizes the shapes and locations of patterns of hypothesized neural activity. These patterns are topographically organized along a two-dimensional surface, and they describe the cross-correlation function of the stimuli as a joint function of frequency and the delay parameter of the cross-correlation operation. In this fashion, lateralization depends upon individual modes of such patterns that are weighed with respect to their straightness (consistency of interaural delay over frequency) and centrality (the extent to which interaural delays are small in magnitude).

Lateralization of bands of noise and sinusoidally amplitude‐modulated tones: Effects of spectral locus and bandwidth

Lateralization of narrow bands of noise was investigated while varying interaural temporal disparity (ITD), center frequency, and bandwidth, utilizing an acoustic pointing task. Stimuli were narrow bands of noise centered at octave intervals between 500 Hz and 4 kHz with bandwidths ranging from 50-400 Hz. In a second experiment, lateralization for bands of noise and sinusoidally amplitude-modulated (SAM) tones, whose spectral content was constrained to be no lower than 3.8 kHz, was assessed. Overall, relatively large extents of laterality were obtained from all four listeners for ITDs of low-frequency bands of noise. Increasing the bandwidth of these noises did not yield consistent changes in the extent of laterality across ITDs and listeners. Most targets centered at high frequencies were lateralized near the midline. However, three of the four listeners did exhibit rather large displacements of the intracranial image when the bandwidth of the high-frequency noises was 400 Hz or greater. Interestingly, ITDs within high-frequency SAM tones were relatively ineffective. Thus, it appears that ITDs of relatively wide-band, high-frequency stimuli can mediate rather substantial extents of laterality. However, these effects are highly listener-dependent.

Discrimination of interaural temporal disparities by normal‐hearing listeners and listeners with high‐frequency sensorineural hearing loss

Thresholds of ongoing interaural time difference (ITD) were obtained from normal-hearing and hearing-impaired listeners who had high-frequency, sensorineural hearing loss. Several stimuli (a 500-Hz sinusoid, a narrow-band noise centered at 500 Hz, a sinusoidally amplitude-modulated 4000-Hz tone, and a narrow-band noise centered at 4000 Hz) and two criteria [equal sound-pressure level (Eq SPL) and equal sensation level (Eq SL)] for determining the level of stimuli presented to each listener were employed. The ITD thresholds and slopes of the psychometric functions were elevated for hearing-impaired listeners for the two high-frequency stimuli in comparison to: the listeners own low-frequency thresholds; and data obtained from normal-hearing listeners for stimuli presented with Eq SPL interaurally. The two groups of listeners required similar ITDs to reach threshold when stimuli were presented at Eq SLs to each ear. For low-frequency stimuli, the ITD thresholds of the hearing-impaired listener were generally slightly greater than those obtained from the normal-hearing listeners. Whether these stimuli were presented at either Eq SPL or Eq SL did not differentially affect the ITD thresholds across groups.

Lateralization of low‐frequency tones: Relative potency of gating and ongoing interaural delays

Several types of interaural delay can affect the lateral position of binaural signals. Delays can occur within the gating (onset and/or offset) or ongoing portions of the signal, or both. Extent of laterality produced by each of these delays was measured for low-frequency tones with an acoustic pointing task. Relative potency was assessed by presenting the delays singly or in combinations (where the types of delay were consistent or in opposition). Rise/decay time, duration, and frequency of the tonal targets were also varied. The major finding was that ongoing delays were much more potent than gating delays in determining extent of laterality. Gating delays were most effective when the interaural phase of the ongoing portion of the tones was more or less ambiguous with respect to which ear was leading. Many of our findings are qualitatively well described by considering properties of patterns of activity produced within a cross-correlation network by such interaurally delayed signals.

COMPARISON OF HEARING THRESHOLDS AND MORPHOLOGICAL CHANGES IN THE CHINCHILLA AFTER EXPOSURE TO 4 kHz TONES

Behavioral, anatomical and histochemical effects of acoustic overstimulation produced by a 4 cHz tone were investigated. In each of five monaural chinchillas, high frequency hearing loss was produced which was related to locus and extent of hair cell loss. Masked audiograms were fairly consistent with those obtained in quiet and the anatomical data on presence or absence of hair cells. Histochemical and electron microscope examination of selected portions of the cochlear partition revealed a series of changes in hair cells which may or may not influence their functional properties.ZUSAMMENFASSUNGDie Wirkungen akustischer uberreizung auf anatomische, histochemische und Verhaltens-Parameter wurden an funf einohrigen Chinchillas untersucht. Beschallung erfolgte mit einem Dauerton von 4 kHz. Die an Hand von Audiogrammen festgestellten Horausfalle stimmten ziemlich gut mit der Lokalisation sowie der Ausdehnung des Haarzellen untergangs im Cortischen Organ uberein. An Haarzellen ausserhalb der Hauptzerstorungsh...

Comparison of critical ratios and critical bands in the monaural chinchilla

The major purpose of this study was to compare measures of critical ratios and critical bands in monaural chinchillas. Critical ratios were obtained from two groups of chinchillas tested at 0.5, 1, 2, and 4 kHz in each of three levels of broad−band noise. Critical bands were obtained by assessing the values of masked threshold in various narrow−bands of noise centered on each test frequency. The measures of critical ratios and critical bands were found not to be parallel as a function of frequency, as is the case for human subjects. The present data were compared to those reported for the monkey and were found to be in essential agreement.Subject Classification: 65.58, 65.75; 80.50.