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PubMed1983

Head and body space to left and right, front and rear--I. Unidirectional competitive auditory stimulation.

Very substantial right ear advantages (REAs) and right side advantages (RSAs) are reported for vocal shadowing latencies to laterally presented competitive verbal stimuli from a single earphone or loudspeaker. When head and body hemispace were dissociated by inducing a 90 degree head turn, with presentations either lateral or front-back with respect to the body, RSAs and REAs vanished, indicating that stimuli neither in the head nor in the body hemispace alone appear capable of generating any lateral asymmetries. However, a front-of-body (but not front-of-head) superiority compared with the rear was obtained. Most importantly, a powerful ventriloquism effect was obtained whereby a laterally placed dummy loudspeaker produced "pseudo"-RSAs with anterior-posterior-located sound sources. This suggests that it is the perceived position of a sound source rather than its actual position or ear of entry which determines asymmetries.

Auditory Perception↗
PubMed1983

Deficits in auditory-spatial integration of sequentially presented patterns due to cortical lesions.

Groups of patients with cortical lesions were subjected to a uniquely developed procedure to test auditory-spatial perception. The stimuli were comprised of a sound source, which sequentially outlined a pattern within a 10 X 10 matrix of loudspeakers. Simple sound patterns, which "moved" across the loudspeaker array only once or twice, were equally well identified by the control group and the various patient groups. However, the more complex patterns, which outlined the contour of alphabetical letters, resulted in significantly lowered identification rates for the patient groups with lesions in the right posterior, left posterior and left temporal lobes. As a control measure, visual-spatial tasks were administered, and lower performance rates were found for the left and right posterior groups. The differences and similarities between auditory spatial and visual-spatial processing are discussed.

Auditory Perception↗
PubMed1986

Dichotic and dichhaptic techniques.

Auditory and tactual asymmetries frequently demonstrate right side advantages for verbal stimuli and the opposite effects for nonverbal stimuli. Such asymmetries may, however, reflect the perceived position of events in space, rather than the role of anatomical afferent pathways with suppression of ipsilateral by contralateral routes. Consequently, despite popular tradition, simultaneous competitive stimulation (dichotic or dichhaptic) may be unnecessary. We review the reliability and the relatively low validity of such techniques for predicting hemispheric specialization in various clinical and normal populations. We discuss the role of stimulus factors, the various indices and measures, the effect of order and mode of report, division of attention, task difficulty and memory factors.

Attention↗
PubMed1987

Lateralization of a moving auditory image in patients with focal damage of the brain hemispheres.

Perception of the moving fused auditory image resulting from dichotic click-train stimulation was studied in 53 patients with focal damages of the temporal lobes. Patients with the right- and left-side damage differed in the click rate for perceived movement and in the movement trajectory length. The data are discussed in connection with right hemisphere specialization for directional hearing.

Adolescent↗
PubMed1989

Parietal lobe mechanisms of spatial attention: modality-specific or supramodal?

Is the spatial attention system divided into separate, modality-specific subsystems, or is there a supramodal spatial attention system? More specifically, does the role of the parietal lobe in spatial attention involve modality-specific or supramodal mechanisms? We addressed this question using a variant of Posner's spatial cuing task. Parietal-lesioned patients performed a simple reaction time task to lateralized visual target stimuli, preceded on each trial by either non-predictive lateralized visual cue stimuli or non-predictive lateralized auditory cue stimuli. With both types of cues, we found disproportionate slowness in responding to invalidly cued contralesional targets, indicative of an impairment in disengaging attention from the ipsilesional to the contralesional side of space. The finding of an attentional disengagement impairment for visual targets with auditory cues implies that the parietal lobe's attentional mechanism operates on a representation of space in which both visual and auditory stimuli are represented, in other words, a supramodal representation of space.

Adult↗
PubMed1990

Recognition of fused dichotic words: an examination of the effects of head-turn and perceived spatial position.

Ear advantages for verbal stimuli were determined for male and female right-handed subjects using a fused dichotic words test. Subjects performed the word recognition task with their heads turned 90 degrees to the left, 90 degrees to the right, and straight ahead. In addition, subjects provided subjective judgements with regard to the perceived spatial position of the sound. A significant right ear advantage was evidenced under all three head turn conditions, although the magnitude of the REA was reduced in the right head turn condition. There was no significant effect of sex. Judgements of perceived spatial position indicated that subjects perceived the fused sound as coming from the centre of the head, regardless of the head's orientation with respect to the body. These findings suggest that ear of entry rather than the perceived position of a sound source is the major factor in determining the perceptual asymmetries observed with dichotic stimuli.

Adult↗
PubMed1991

The influence of attention on the dichotic REA.

Laterality researchers have frequently neglected to control for possible attentional components of perceptual asymmetries. Attention was manipulated in a dichotic listening paradigm by presenting a pre-exposural tone cue to the ear from which the subject was required to report. The time period between the onset of the cue and the onset of the trial (Stimulus Onset Asynchrony--SOA) was varied such that the time available to orient attention was manipulated. In two experiments, sizeable REAs were apparent at the shortest SOA (150 msec) but were substantially attenuated at longer intervals (450 and 750 msec SOA). In addition, a much larger effect of SOA on left-ear than on right-ear performance was observed. These effects were taken as evidence of an attentional bias to the right ear in the typical dichotic listening situation.

Adult↗
PubMed1993

Children's ability to shift attention from one ear to the other: divergent results for dichotic and monaural stimuli.

In three experiments, 5- to 8-year-old children reported digit names from one ear for 30 trials before shifting attention to the other ear. Stimuli were presented dichotically in Experiment 1 and monaurally in Experiments 2 and 3. Dichotic stimulation yielded not only a right-ear advantage but also a priming effect that reflects difficulty in shifting attention in either direction. With monaural stimulation, however, performance with the second ear to be monitored was superior to performance with the first ear. The priming effect thus depends on interaural competition and cannot be attributed to general factors such as fatigue or motivation.

Attention↗
PubMed1996

Differences between Caucasians and American Indians on the cognitive laterality battery.

Caucasians scored significantly better than American Indian college students on verbal-sequential tests, but not on visuospatial tests, of Gordon's Cognitive Laterality Battery (CLB). Caucasians scored more right-biased than American Indians on the Edinburgh Handedness Inventory (EHI). The effects of percentage of Native American ancestry, strategy employed to recall serial sounds, bilingualism, familial sinistrality and handedness laterality on test performance were also analyzed. Results are consistent with hypotheses drawn from Annett's genetic theory of human laterality, if frequency distributions for the hypothesized rs+ gene are assumed to vary across the parent populations from which the samples were drawn.

Acoustic Stimulation↗
PubMed1983

Attentional biases and the right-ear effect in dichotic listening.

Most dichotic listening experiments permit subjects to deploy attention in any way they choose. We argue that this adds uncontrolled variance to the observed right-ear advantage. In the first experiment, more robust laterality effects were obtained in an identification task with focused than with divided attention. Such differences were not found in the second experiment, when a detection procedure was used. Virtually all the laterality effect observed in the second study could be attributed to subjects who were biased attenders, in the sense that they exhibited more intrusions from the right ear to the left than vice versa. However, rather than indicating that laterality effects are simply attentional bias, this effect can be attributed to an asymmetry of perceptual discrimination.

Adolescent↗
PubMed1983

Central auditory processing. IV. Ear dominance--spatial and temporal complexity.

Ear dominance for dichotically presented tones was measured in 63 righthanded subjects when the frequency difference (delta f) was small compared to the center frequency (fc) and again when it was large. Although two-thirds of the population exhibited a left-ear dominance in both conditions, a shift toward right-ear dominance occurred when the delta f was increased. An additional study, employing the alternating tone illusion described by Deutsch, revealed the same general effect, i.e., a shift toward right-ear dominance with increasing values of delta f/fc. The results of these experiments, coupled with a review of previously published data of other dichotic experiments, indicate that as the ratio of delta f/fc increases, the subjective complexity of the sound image increases, and there is a progressive emergence of a "right-ear advantage" (or ear dominance). A tentative explanation relates these results to the effects of anatomical asymmetries of primary and auditory association cortex and the efferent temporal lobe enhancement mechanism described by R. Efron, P.H. Crandall, B. Koss, P.L. Divenyi, and E.W. Yund (Brain and Language, 1983, 19, 254-263.

Adolescent↗
PubMed1987

Spatial constraints on attention to speech in the blind.

When sighted persons try to identify one of two speech utterances coming from different directions, they display both a frontal position advantage, i.e., better recognition of inputs from the front than of those from the rear, and a right-side advantage, better recognition of inputs from the right than of those from the left. The present study demonstrates a dissociation of the two effects in blind subjects (N = 10) who showed no frontal position advantage together with a right-side advantage superior to that of control sighted subjects (N = 16). There was no systematic difference between congenitally blind subjects and noncongenitals. The absence of frontal position advantage in the blind is consistent with the notion that this effect originates in the habit of sighted listeners to orient toward the source of heard speech. The occurrence of at least normal right-side advantage in the blind does not support recent suggestions of reduced lateralization of language functions in such subjects.

Adolescent↗
PubMed1988

Expectancy effects: cost-benefit analysis of monaurally and dichotically presented speech.

In three experiments, cost-benefit analysis was used to determine the role of attention in the processing of auditory information. In two experiments consonant-vowel syllables were presented monaurally, while in the third the mode of presentation was dichotic. For all three experiments the ability to detect a target stimulus under conditions in which precued location information was valid or invalid was contrasted with detection in a neutral condition where no location information was provided. The results indicated that attention can be effectively deployed under monaural conditions when either a simple detection or a discriminative response is required. Similar conclusions cannot be reached when considering the effectiveness of attention under conditions of dichotic listening. These results are discussed in relation to accounts which argue that dichotic listening performance is critically dependent upon auditory disembedding and where attention is viewed as a late process involving response selection.

Adult↗
PubMed1990

The effects of head and eye turns on the right ear advantage in dichotic listening.

The aim of the present experiment was to investigate the effects of head and eye turns on the ear advantage in dichotic listening (DL) to CV-syllables. Since head and eye turns also mean focusing attention to either the left or right side in space, a second aim was to evaluate recent arguments that ear advantages seen in DL are caused by the perceived position in space of the sound source. Forty right-handed females had 36 trials of CV-syllables under four different instructions. One group (n = 20) was instructed to turn their head (but not their eyes) to the right, the left, or straight ahead during stimulus presentations. The fourth condition was a standard (no instruction) condition. A second group (n = 20) had the same instructions but were told to turn their eyes instead of their heads. Conditions were pseudo-counterbalanced across subjects. Consistent with other studies, results showed a right ear advantage (REA) in both groups during all conditions. However, the REA was largest for the standard condition. Also, more subjects showed a REA during the standard condition, and especially compared to the turn-right condition. It is concluded that dichotic performance is not caused by selective attention to either side in space, and that lateral turns of the head and the eyes contralateral to the left hemisphere have an inhibitory (if anything) effect on the REA.

Adult↗
PubMed1995

The developmental emergence of the representation of auditory azimuth in the external nucleus of the inferior colliculus of the guinea-pig: the effects of visual and auditory deprivation.

A topographic representation of the auditory azimuth has been described in the external nucleus of the inferior colliculus (ICX) of the guinea-pig [3]. This representation is characterized by directional multi-unit responses, at threshold stimulation intensities, with directional preferences organized in such a way as to represent the auditory azimuth along the rostro-caudal axis of the ICX. The following paper considers the emergence of that map and the role of developmental experience in its elaboration. Multi-unit responses to free-field broad-band auditory stimuli were recorded in the ICX. At threshold stimulation intensities, multi-unit receptive fields (MURFs) obtained from younger animals showed the same discrete spatial tuning as found in MURFs from animals older than 35 DAB (days after birth). However, a normal adult topographic representation was not present until animals were at least 30-32 DAB. Visual deprivation, by dark-rearing from birth until mapping (at 35-43 DAB), had no obvious detrimental effects on auditory receptive field size or topographic order in the ICX. Auditory deprivation was achieved by rearing animals in an environment of continuous omnidirectional noise from birth until mapping (47-53 DAB). Following auditory deprivation, receptive fields remained relatively discrete, but no correlation between rostro-caudal position of the recording site and the angle of the best response was observed. Thus, the representation of auditory azimuth in the ICX appears to be unperturbed by developmental visual deprivation but is susceptible to developmental auditory deprivation.

Animals↗
PubMed1992

Role of the central auditory system in hearing: the new direction.

The mammalian central auditory system contains a large number of subcortical auditory nuclei, which were once thought to form a simple relay system, taking signals from the ear to the cortex where all information processing would have occurred. Now it appears that these subcortical nuclei are themselves responsible for the extraction and analysis of the dimensions of sounds. Not only do the nuclei encode dimensions defining the nature of the sound, but also they extract features of sound location. Three major nuclei in the superior olivary complex of mammals extract the horizontal direction of a sound source, and it seems likely that other nuclei in the auditory system encode elevation and distance. This shift in viewpoint away from the attributes of sound to the attributes of sound sources is an important new step in the investigation of the role of the central auditory system in hearing.

Acoustic Stimulation↗
PubMed1990

Impairment of auditory processing by simultaneous vestibular stimulation: psychophysical and electrophysiological data.

The aim of the experiments reported here was to demonstrate auditory-vestibular interaction both on a psychophysical and on an electrophysiological basis in humans. These results correspond to those recently obtained during simultaneous visual and vestibular stimulation and illustrate experimentally the importance of auditory information processing in spatial orientation. Time to detect the motion of a sound source is significantly increased when simultaneous vestibular stimulation is induced by passive sinusoidal head oscillations. This effect increased with the peak acceleration of the vestibular stimulus (197, 790 and 1777 degrees/s2). Vestibular influence on general auditory information processing without the quality of (object-) motion could be electrophysiologically demonstrated by means of brainstem auditory evoked potentials. The amplitude of component V generated by the inferior colliculi or by neuronal structures located slightly lower in the auditory tract was significantly reduced during concurrent vestibular stimulation. This neuronal brainstem area is a predominant location of biconvergent vestibulo-auditory neurons mediating intersensory information processing at an early neuronal level.

Adolescent↗