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At least 1,531 records · Page 85Linked to original sources
PubMed2001

Deficit of auditory space perception in patients with visuospatial neglect.

There have been many studies of visuospatial neglect, but fewer studies of neglect in relation with other sensory modalities. In the present study we investigate the performance of six right brain damaged (RBD) patients with left visual neglect and six RBD patients without neglect in an auditory spatial task. Previous work on sound localisation in neglect patients adopted measure of sound localisation based on directional motor responses (e.g., pointing to sounds) or judgement of sound position with respect to the body midline (auditory midline task). However, these measures might be influenced by non-auditory biases related with motor and egocentric components. Here we adopted a perceptual measure of sound localisation, consisting in a verbal judgement of the relative position (same or different) of two sequentially presented sounds. This task was performed in a visual and in a blindfolded condition. The results revealed that sound localisation performance of visuospatial neglect patients was severely impaired with respect to that of RBD controls, especially when sounds originated in contralesional hemispace. In such condition, neglect patients were always unable to discriminate the relative position of the two sounds. No difference in performance emerged as a function of the visual condition in either group. These results demonstrate a perceptual deficit of sound localisation in patients with visuospatial neglect, suggesting that the spatial deficits of these patients can arise multimodally for the same portion of external space.

Adult↗
PubMed2002

Selective deficit of auditory localisation in patients with visuospatial neglect.

Possible auditory deficits in neglect were examined by comparing the performance of four right brain-damaged (RBD) patients with left visuospatial neglect, versus four RBD patients without neglect, in three auditory tasks. The first task required speeded discrimination of sound elevation, by moving a central lever up or down according to the vertical position of a peripheral target sound, regardless of its side. The other two auditory tasks were non-spatial, requiring either speeded pitch discrimination (moving the central lever up for high pitch, down for low pitch) or speeded target detection. Neglect patients' performance was impaired with respect to RBD controls only when the auditory task required spatial coding of the target sound (the up/down spatial discrimination). This demonstrates a selective deficit of auditory space perception in neglect patients. This auditory spatial deficit was more pronounced for left than right sounds. Since auditory space perception was impaired in the vertical dimension, the observed deficit cannot be attributed to a systematic rightward shift in sound localisation. Instead, the results suggest increased spatial uncertainty in sound localisation by neglect patients, particularly for auditory targets on the contralesional side. These findings are related to multimodal coding of space in the parietal cortex, which was damaged in the neglect patients, but not in the RBD controls.

Adult↗
PubMed2002

Impaired perception of temporal order in auditory extinction.

It has been proposed that patients with extinction show a chronic bias of spatial attention towards the ipsilesional side. In this case, the law of 'prior entry' predicts that ipsilesional events should be perceived earlier than physically synchronous contralesional stimuli. In line with this prediction, previous studies have revealed substantial delays of awareness for contralesional visual and tactile events in patients with visual and with tactile extinction. The present study provides evidence that a 'prior entry' bias also occurs in the auditory modality. Patients with auditory extinction perceived two acoustic events (one presented to the left ear, the other to the right ear) as being 'simultaneous' when the contralesional sound was leading by 270 ms. The magnitude of this asynchrony was quite similar to that measured previously in the visual modality. Thus, the pathological delay of awareness for contralesional events may be independent of the sensory modality of the stimuli.

Acoustic Stimulation↗
PubMed2003

Preserved use of spatial cues for sound segregation in a case of spatial deafness.

Auditory spatial cues contribute to sound localisation and to sound object segregation. We have investigated these capacities in a patient (NM) who complained having difficulties to localise sounds in everyday life after a right temporo-parieto-frontal ischemic lesion. Two groups of tasks were used, in which spatial dimension was simulated by interaural time differences (ITD): (i) active localisation of stationary or moving sound targets, and (ii) sound segregation on the basis of spatial cues. This latter included a spatial release from masking paradigm and two ITD diotic tasks. NM failed to localise stationary and moving sounds: she perceived all the stimuli at the centre of the head, and could not differentiate stationary from moving targets. In contrast, NM was able to use ITD cues to segregate simultaneous sound sources in the spatial-release-from-masking paradigm and in ITD diotic tasks.These results suggest that sound localisation and sound object segregation based on spatial cues do not rely on the same mechanisms.

Adult↗
PubMed2000

Auditory agnosia and auditory spatial deficits following left hemispheric lesions: evidence for distinct processing pathways.

Auditory recognition and auditory spatial functions were studied in four patients with circumscribed left hemispheric lesions. Patient FD was severely deficient in recognition of environmental sounds but normal in auditory localisation and auditory motion perception. The lesion included the left superior, middle and inferior temporal gyri and lateral auditory areas (as identified in previous anatomical studies), but spared Heschl's gyrus, the acoustic radiation and the thalamus. Patient SD had the same profile as FD, with deficient recognition of environmental sounds but normal auditory localisation and motion perception. The lesion comprised the postero-inferior part of the frontal convexity and the anterior third of the temporal lobe; data from non-human primates indicate that the latter are interconnected with lateral auditory areas. Patient MA was deficient in recognition of environmental sounds, auditory localisation and auditory motion perception, confirming that auditory spatial functions can be disturbed by left unilateral damage; the lesion involved the supratemporal region as well as the temporal, postero-inferior frontal and antero-inferior parietal convexities. Patient CZ was severely deficient in auditory motion perception and partially deficient in auditory localisation, but normal in recognition of environmental sounds; the lesion involved large parts of the parieto-frontal convexity and the supratemporal region. We propose that auditory information is processed in the human auditory cortex along two distinct pathways, one lateral devoted to auditory recognition and one medial and posterior devoted to auditory spatial functions.

Aged↗
PubMed1989

Sensorineural hearing loss.

The authors emphasize the importance of early identification and early intervention concerning the management of children with Sensorineural Hearing Loss. The pediatrician plays a critical role in initiating the necessary clinical and audiological evaluations. Guidelines and treatment options are reviewed.

Child, Preschool↗
PubMed2002

The latency of saccades toward auditory targets in humans.

Auditory targets can be used to evoke saccadic eye movements since they provide a position reference signal in space. Comparison of the characteristics of saccades evoked by both visual and auditory stimuli can give further information on the oculomotor control system. In particular, the latency of auditory saccades evoked in different experimental situations, such as the step, gap and overlap protocols, and with different starting positions of the eyes in the orbit can provide useful insight into the central processing underlying saccade generation. The aim of this chapter is to provide a review of auditory saccade characteristics and to present latency data obtained in human subjects in different experimental conditions.

Acoustic Stimulation↗
PubMed2006

The "other" transformation required for visual-auditory integration: representational format.

Multisensory integration of spatial signals requires not only that stimulus locations be encoded in the same spatial reference frame, but also that stimulus locations be encoded in the same representational format. Previous studies have addressed the issue of spatial reference frame, but representational format, particularly for sound location, has been relatively overlooked. We discuss here our recent findings that sound location in the primate inferior colliculus is encoded using a "rate" code, a format that differs from the place code used for representing visual stimulus locations. Possible mechanisms for transforming signals from rate-to-place or place-to-rate coding formats are considered.

Analysis of Variance↗
PubMed2001

Synthesizing spatially complex sound in virtual space: an accurate offline algorithm.

The study of spatial processing in the auditory system usually requires complex experimental setups, using arrays of speakers or speakers mounted on moving arms. These devices, while allowing precision in the presentation of the spatial attributes of sound, are complex, expensive and limited. Alternative approaches rely on virtual space sound delivery. In this paper, we describe a virtual space algorithm that enables accurate reconstruction of eardrum waveforms for arbitrary sound sources moving along arbitrary trajectories in space. A physical validation of the synthesis algorithm is performed by comparing waveforms recorded during real motion with waveforms synthesized by the algorithm. As a demonstration of possible applications of the algorithm, virtual motion stimuli are used to reproduce psychophysical results in humans and for studying responses of barn owls to auditory motion stimuli.

Acoustic Stimulation↗
PubMed1999

Contralateral induction by frequency spectrum in hallucinating schizophrenics.

Seventeen schizophrenic patients who had all experienced auditory hallucinations were compared with 14 subjects of a reference group on a test of contralateral induction. Contralateral induction means that a sound is illusively heard as coming from a location where it belongs according to its spectral content. The phenomenon is connected with a simultaneous relative elimination of masking. The schizophrenic subjects deviated from the reference group in several aspects. Some of them did not hear the sound being induced to the contralateral side, which it was for all reference subjects. Another subgroup of the schizophrenics noticed the induction unusually early with a prolonged experience of it, and finally some of them experienced the induction now and then. The aberrations were interpreted as rigidity of adaptation on the one hand and as effects of an enhanced sensitivity on the other. Discontinuity, meaning that the fluency in mental processing is broken, was interpreted to cause the ratings of the third group of schizophrenics in this sample, who heard the contralateral induction now and then. These phenomena are clearly reminiscent of descriptions in research reports, and witnessed by clinical experience of the schizophrenic disturbance. The results represent another example of discontinuous neurophysiological functions between neural systems and between individuals suffering from schizophrenia.

Adult↗
PubMed2003

Sound analysis in auditory cortex.

Not so long ago, the auditory cortex took a back seat to the visual system in neuroscience research. With some notable exceptions outside the primate order, such as the classic work on echo-locating bats, owls and birdsong, the auditory cortex has been overlooked: only a few investigators were involved in understanding the structure and function of the monkey auditory cortex, and even fewer had the means to study its human counterpart. This situation has undergone a dramatic change in the past decade or so. Spurred on by advances in primate neurophysiology and neuroanatomy, and especially by developments in functional neuroimaging, substantial progress is now being made into understanding how the human auditory cortical system works.

Animals↗
PubMed1999

Maps versus clusters: different representations of auditory space in the midbrain and forebrain.

The auditory system determines the location of stimuli based on the evaluation of specific cues. The analysis begins in the tonotopic pathway, where these cues are processed in parallel, frequency-specific channels. This frequency-specific information is processed further in the midbrain and in the forebrain by specialized, space-processing pathways that integrate information across frequency channels, creating high-order neurons tuned to specific locations in space. Remarkably, the results of this integrative step are represented very differently in the midbrain and forebrain: in the midbrain, space is represented in maps, whereas, in the forebrain, space is represented in clusters of similarly tuned neurons. We propose that these different representations reflect the different roles that these two brain areas have in guiding behavior.

Animals↗
PubMed1999

Auditory cortical plasticity: a comparison with other sensory systems.

The auditory cortex has a crucial role in higher cognitive functions, including the perception of speech, music and auditory space. Cortical plasticity, as in other sensory systems, is used in the fine tuning of the auditory system for these higher functions. Auditory cortical plasticity can also be demonstrated after lesions of the cochlea and it appears to participate in generating tinnitus. Early musical training leads to an expansion in the representation of complex harmonic sounds in the auditory cortex. Similarly, the early phonetic environment has a strong influence on speech development and, presumably, on the cortical organization of speech. In auditory spatial perception, the spectral cues generated by the head and outer ears vary between individuals and have to be calibrated by learning, which most probably takes place at the cortical level. The neural mechanisms of plasticity are likely to be the same across all cortical regions. It should be useful, therefore, to relate some of the findings and hypotheses about auditory cortical plasticity to previous studies of other sensory systems.

Animals↗