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Biomedical subjects

N I Hill

Publications and source records attributed to N I Hill.

9 recordsLinked to original sources
PubMed2000

Auditory spatial attention using interaural time differences.

Previous probe-signal studies of auditory spatial attention have shown faster responses to sounds at an expected versus an unexpected location, making no distinction between the use of interaural time difference (ITD) cues and interaural-level difference cues. In 5 experiments, performance on a same-different spatial discrimination task was used in place of the reaction time metric, and sounds, presented over headphones, were lateralized only by an ITD. In all experiments, performance was better for signals lateralized on the expected side of the head, supporting the conclusion that ITDs can be used as a basis for covert orienting. The performance advantage generalized to all sounds within the spatial focus and was not dissipated by a trial-by-trial rove in frequency or by a rove in spectral profile. Successful use by the listeners of a cross-modal, centrally positioned visual cue provided evidence for top-down attentional control.

Adult↗
PubMed1999

Sequential effects in rudimentary auditory and visual tasks.

Three experiments examined sequential effects in choice reaction time tasks. On each trial, a right/left positional judgment was made to a either a pure tone or a luminance increment in a visual array of box elements. In the first two experiments, a preparatory signal was presented prior to each imperative signal to indicate the relevant stimulus modality. At a short stimulus onset asynchrony (SOA) between the preparatory and the imperative signal (i.e., 60 msec), subjects were quicker to repeat the same response than to change their response when presented with successive tones, although no such repetition effect occurred on the visual target trials. Subjects were impaired if the stimulus modality changed across successive trials regardless of the modality of the target. At a longer SOA (i.e., 500 msec), these sequential effects were abolished; subjects were assumed to be able to prepare for the relevant modality because of the presentation of the preparatory signal. When the preparatory signals were omitted, in a final experiment, the modality-switching costs were still evident, but now inhibition of return occurred on both the auditory and the visual target trials-subjects were now impaired in responding when the target reappeared at its immediately previous location. It seems, therefore, that the repetition effect and modality-switching effects do dissociate. The data revealed clear differences between orienting attention to a particular spatial locale and focusing attention to a particular sensory modality.

Attention↗
PubMed1998

Relative intensity comparisons between a tone and spectrally remote noise: effects of onset asynchrony.

The present experiment investigated the effect of onset asynchrony on listeners' ability to make relative intensity comparisons between a 1-kHz tone and a band of noise high-pass filtered at 3 kHz. In the synchronous condition, the tone and noise were gated on and off simultaneously. In the two asynchronous conditions, either the tone was gated on before the noise or vice versa, both stimuli terminating simultaneously. In the sequential condition, the offset of the tone coincided with the onset of the noise. The task of the six listeners was to indicate in which of the two presentation intervals the level of the tone was incremented relative to that of the noise. To deter the use of strategies based on successive, within-channel level comparisons, the overall level of the stimuli was randomized on each presentation. For all listeners thresholds were lowest in the synchronous condition, and highest in the sequential condition, the difference ranging from approximately 7 to 18 dB (signal re: pedestal amplitude). Furthermore, five of the six listeners had significantly lower thresholds in the noise-leading condition than in the tone-leading condition, the average difference across listeners being approximately 5 dB. The results are discussed in terms of auditory grouping and the possible strategies available to the listeners.

Acoustic Stimulation↗
PubMed1998

Across-channel intensity discrimination in the presence of an interferer.

Listeners' thresholds for discriminating changes in the relative intensities of two octave-spaced pure tones were measured in three conditions using a 2AFC procedure. In the baseline condition the tone pair was presented alone, while in the two interference conditions the tone pair was accompanied by four additional tones, with the frequency separation between adjacent components of the resultant six-component complex being one octave. In the interference conditions the flanking components were either gated synchronously with the target pair, or began 200 ms ahead. The level of the flanking components relative to the target was randomized on each presentation. The overall stimulus level was also randomized on each presentation to reduce the effectiveness of within-channel comparisons. Threshold elevations in the synchronous condition relative to the baseline ranged from approximately 5 to 17 decibels. By contrast, in the asynchronous condition only one listener showed significant (although substantially reduced) interference. The results complement previous observations that across-channel intensity comparisons are poorer between components that begin or end at different times, and are qualitatively consistent with the hypothesis that temporal misalignment promotes the perceptual segregation of simultaneous frequency components.

Adult↗
PubMed1997

A probe-signal study of auditory discrimination of complex tones.

The present experiments used an analogue of the probe-signal method of Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513-1523 (1968)] to investigate the extent to which listeners direct attention to a particular spectral region when discriminating complex tones. The listeners' task was to discriminate between two seven-component complex tones on the basis of an increment in the level of a single component. On two-thirds of trials the increment was achieved by adding a fixed primary signal to one component of the complex. The primary-signal trials were relatively easy and were intended to cue listeners to attend to the component to which the primary was added. On the remaining trials a smaller probe signal was added either to the cued component, or to one of three other components. The results of the first experiment, in which the complex tones had a flat spectrum, showed significantly better performance for probe signals applied to the cued component compared to the other three components. To control for the possibility that the observed pattern of results was due to the use of timbral cues, a second experiment was conducted in which the spectral profile of the tones was randomized between trials. The results for the second experiment were similar to those of the first experiment and are consistent with the idea that listeners were focusing attention on the spectral region defined by the primary signal.

Adult↗
PubMed1997

Profile analysis with an asynchronous target: evidence for auditory grouping.

Green and Dai [in Auditory Physiology and Perception, edited by Y. Cazals, L. Demany, and K. Horner (Pergamon, Oxford, 1992)] reported a series of experiments which suggested that listeners' ability to perform simultaneous across-frequency comparisons of intensity is severely impaired when the target and flanking components begin or end at different times. The present experiment sought to replicate the effect of onset asynchrony and included an additional condition in which the leading portion, of the asynchronous target component was accompanied by a pair of "captor" tones. The intended purpose of the captor tones was to promote a perceptual organization in which the leading and synchronous portions of the asynchronous target component were grouped with different auditory objects. For all six listeners an asynchrony of 320 ms raised thresholds substantially relative to the synchronous onset condition, the magnitude of the increase ranging between 6 and 16 dB. By contrast, the mean elevation of threshold in the presence of the captor was only 3 dB, although for all listeners thresholds were still greater than for the synchronous onset condition. The results support the view that the deleterious effect of onset asynchrony on profile analysis performance is due to the operation of auditory grouping principles.

Adult↗
PubMed1996

Lateralization of a perturbed harmonic: effects of onset asynchrony and mistuning.

The lateralization paradigm of Trahiotis and Stern [C. Trahiotis and R. M. Sern, J. Acoust. Soc. Am. 86, 1285-1293 (1989)] was extended to investigate the influence of a spectrally flanking complex on the lateral position of a perturbed harmonic. When a complex tone consisting of harmonics 2 through 8 or 100 Hz was presented with an interaural time difference (ITD) of 1.5 ms, the complex was heard on the leading side (experiment 1). However, when the 500-Hz component had a later onset time than the other components (experiments 1 and 2) or was mistuned (experiment 3), it was perceived to be in a different lateral position to the complex. The complex still maintained a residual influence on the lateralization of the pure tone even for the largest asynchrony used (experiment 4). Experiment 5 confirmed that the lateralizaiton of the tonal complex was consistent with the aggregation of binaural information across frequency. The results suggest that across-frequency integration of interaural-timing information is influenced by onset-asynchrony and harmonicity.

Adolescent↗