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Biomedical subjects

C Trahiotis

Publications and source records attributed to C Trahiotis.

52 records · Page 3Linked to original sources
PubMed1986

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.

Acoustic Stimulation↗
PubMed1986

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 listener's 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.

Acoustic Stimulation↗
PubMed1986

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.

Acoustic Stimulation↗
PubMed1986

Lateralization of low-frequency tones and narrow bands of noise.

It is well known and universally accepted that people's ability to use ongoing interaural temporal disparities conveyed via pure tones is limited to frequencies below 1600 Hz. We wish to determine if this limitation is the result of the constant amplitude and periodic axis-crossings which characterize pure tones. To this end, an acoustic pointing task was employed in which listeners varied the interaural intensitive difference of a 500-Hz narrow-band noise (the pointer) so that the position of its intracranial image matched that of a second, experimenter-controlled stimulus (the target). Targets were either pure tones or narrow bands of noise (50 or 100 Hz wide). The narrow bands of noise were delayed interaurally in two distinct manners: Either the entire waveform or only the carrier was delayed. In the latter case, the envelopes and phase-functions of the bands of noise were identical interaurally. This resulted in noises which resemble the pure tone case in that the interaural delay is manifested as a constant phase-shift and resemble ordinary noises in that the envelope and phase are random functions of time. Surprisingly, it appears that all three targets were lateralized virtually identically regardless of frequency or bandwidth. Apparently, the dynamically changing envelopes and phases did not affect the listeners' use of interaural temporal disparities in any discernible fashion.

Acoustic Stimulation↗
PubMed1985

Lateralization of low-frequency, complex waveforms: the use of envelope-based temporal disparities.

Several recent investigations suggest that listeners either cannot or do not use envelope-based interaural temporal disparities (ITDs) to lateralize low-frequency sounds [G.B. Henning, J. Acoust. Soc. Am. 68, 446-453 (1980); G.B. Henning and J. Ashton, Hear. Res. 4, 185-194 (1981); G.B. Henning, Hear. Res. 9, 153-172 (1983)]. We believe listeners in those studies may have been unable to process envelope-based ITDs principally because of the types of stimuli utilized. In this study we employed an acoustic "pointing" task in which listeners varied the interaural intensitive difference of a 500-Hz narrow-band noise (the pointer) so that it matched the intracranial position of a second, experimenter-controlled stimulus (the target). Targets were sinusoidally amplitude-modulated tones centered on 500 Hz or 1 kHz, and modulated at 25, 50, or 100 Hz. Targets were presented with either the entire waveform delayed or with only the envelope delayed. The results suggest that delays of the envelope do affect the lateral position of low-frequency targets. However, the envelope-based cues appear to interact with those provided by the dominant fine structure.

Attention↗
PubMed1985

Lateralization of sinusoidally amplitude-modulated tones: effects of spectral locus and temporal variation.

It has long been recognized that listeners are sensitive to interaural temporal disparities (ITDs) of low-frequency (i.e., below 1600 Hz) stimuli. Within the last three decades, it has often been demonstrated that listeners are also sensitive to ITDs within the envelope of high-frequency, complex stimuli. Because these studies, for the most part, employed discrimination tasks, few data exist concerning the extent of laterality produced by ITDs as a function of the spectral locus of the stimulus. To this end, we employed an acoustic "pointing" task in which listeners varied the interaural intensity difference of a 500-Hz narrow-band noise (the pointer) so that it matched the intracranial position of a second, experimenter-controlled stimulus (the target). Targets were sinusoidally amplitude-modulated tones centered on 500 Hz, 1, 2, 3, or 4 kHz and modulated at rates ranging from 50 to 800 Hz. Targets were presented with either the entire waveform delayed or with only the envelope delayed. Our results suggest that: (1) for low-frequency targets, lateralization is influenced by ITDs in the envelope but is dominated by ITDs in the fine structure; (2) for high-frequency targets, envelope-based delays produce displacements of the acoustic images which are affected greatly by the rate of modulation; rather large extents of laterality could be produced with high rates of modulation; these data are consistent with those obtained previously in discrimination experiments; (3) for low rates of modulation (e.g., 100 Hz), delays of the entire waveform (both envelope and fine structure) produce much greater displacements of the acoustic image for low-frequency than for high-frequency targets (where fine-structure-based cues are not utilizable); (4) there appear to be no consistent relations among extent of laterality, rate of modulation, and the frequency of the carrier within and across listeners.

Adult↗
PubMed1980

Two-tone masking in normal hearing listeners.

Psychophysical measurements of two-tone masking [E. Zwicker, Acustica 4, 415-420 (1954)] were made at 0.25, 0.5, 1, 2, and 4 kHz utilizing a masker level of 62 dB SPL/tone. Fifty-eight "untrained" subjects were tested using a single run of a 4IFC adaptive procedure for each condition. Individual data were highly variable. Average data were systematic; they were analyzed using a two-line-regression procedure and the obtained critical-bandwidth estimates approximated normative values. Analysis of the literature revealed that a substantial increase of estimated critical bandwidth versus masker level occurs in two-tone masking. A portion of this increase appears artificial and stems from the relative effectiveness of the higher frequency masker tone at high masker levels. An alternative masker-frequency spacing is suggested to reduce level effects. Implications for an underlying critical-band mechanism are discussed.

Adolescent↗
PubMed1978

Regression interpretation of differences in time-intensity trading ratios obtained in studies of laterality using the method of adjustment.

This paper proposes a regression interpretation of the laterality matching data recently reported by Young and Levine [J. Acoust. Soc. Am. 61, 607-609 (1977)]. Under this interpretation, the difference between the trading function obtained when delta t is adjusted and that when delta I is ascribed to a judgmental bias associated with the method of adjustment. Arguments against associating the results of Young and Levine with the issue of dual images are presented.

Auditory Perception↗
PubMedDate not supplied

Effect of trial-by-trial variation in center frequency on detection of interaural temporal and intensitive differences in bands of noise.

Sensitivity to interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) was measured as a function of duration in conditions where the center frequency (CF) of the stimuli was constant and, separately, in conditions where the CF of the stimuli was varied on a trial-by-trial basis. Stimuli were bands of noise centered at either 300, 1200, 2400, or 4800 Hz with the bandwidth of the noise being 40% of their CF. The largest effects of shortening duration and varying center CF of the stimuli were degradations of sensitivity to ITDs for stimuli centered at 2400 or 4800 Hz. Overall, the data confirm and extend previous findings which indicate that ITDs and IIDs are processed separately within the central nervous system.

Acoustic Stimulation↗