Biomedical subjects

Jörg Lewald

Publications and source records attributed to Jörg Lewald.

At least 19 recordsLinked to original sources

PubMed2007

Functional cerebral asymmetry in auditory motion perception.

Several studies have shown a right-hemispheric advantage for sound localisation. However, most of these studies used stationary sound stimuli, although in most everyday situations humans are in motion when localising sound, or face a moving sound source. To elucidate the question of a functional asymmetry in cortical processing of auditory motion information, we tested 23 neurologically healthy human participants. Virtual leftward or rightward motion (broadband noise) was presented with variable movement angles (MA) in the horizontal plane (via headphones) in either the participants' left or right hemispace. Participants had to indicate whether the sound moved left or rightward. The frequency of "right" judgements determined as a function of MA had a sigmoidal shape in both hemispaces, indicating significant overall discrimination of motion direction. However, the frequency of correct judgements revealed a significantly better performance for the left than for the right hemispace, suggesting a superiority of the right hemisphere. This finding is in agreement with recent neuroimaging results showing higher right-hemispheric activity during localisation of moving sounds. The results might also point to a supramodal right-hemisphere advantage in the attentional processing of motion perception.

Adolescent↗

PubMed2006

More accurate sound localization induced by short-term light deprivation.

Crossmodal reorganization processes in the brain are mainly associated with early blindness, on the assumption that recruitment of genuine visual areas, such as primary visual cortex, for non-visual functions results in superior auditory and tactile performance of blind, compared to sighted, humans. This study shows that in sighted subjects the accuracy of sound localization, measured by a task of head pointing to acoustic targets, is reversibly increased after short-term light deprivation of 90 min. However, only the systematic deviations from target positions (constant error) were reduced after light deprivation, while the general precision of head pointing remained unchanged. Return to pre-deprivation values was observed after 180 min of re-exposure to light. The post-deprivation change was similar, though less in magnitude, to the effect of blindness that was demonstrated previously. Generally, these findings indicate that auditory-visual crossmodal plasticity can be quite rapidly initiated by deprivation of the visual cortex from visual input. It seems possible that visual deprivation has an influence on neuronal circuits, that are involved in processing of auditory information in visual brain areas of normal sighted humans. Since exclusively the constant error in sound localization, not general performance, was changed, the present effect of visual deprivation may, however, not be attributable to reorganization processes in the sense of a compensation for the absence of vision. It is more likely that the observed change in accuracy was specifically induced by the absence of visual calibration of the neural representation of auditory space during light deprivation.

Acoustic Stimulation↗

PubMed2006

Horizontal and vertical effects of eye-position on sound localization.

The effect of gaze direction on the localization of sound sources was investigated in the azimuthal and elevational dimension using a pointing task. In both dimensions, eccentric eye-position induced a significant shift in sound localization that was opposite to the direction of eccentricity. This finding is in accordance with the view that the azimuthal and elevational components of the auditory spatial information are processed in common neural substrates.

Acoustic Stimulation↗

PubMed2005

Sound lateralization in subjects with callosotomy, callosal agenesis, or hemispherectomy.

The question of whether there is a right-hemisphere dominance in the processing of auditory spatial information in human cortex as well as the role of the corpus callosum in spatial hearing functions is still a matter of debate. Here, we approached this issue by investigating two late-callosotomized subjects and one subject with agenesis of the corpus callosum, using a task of sound lateralization with variable interaural time differences. For comparison, three subjects with left or right hemispherectomy were also tested by employing identical methods. Besides a significant reduction in their acuity, subjects with total or partial section of the corpus callosum exhibited a considerable leftward bias of sound lateralization compared to normal controls. No such bias was found in the subject with callosal agenesis, but merely a marginal reduction of general acuity. Also, one subject with complete resection of the left cerebral cortex showed virtually normal performance, whereas another subject with left hemispherectomy and one subject with right hemispherectomy exhibited severe deficits, with almost total loss of sound-lateralization ability. The results obtained in subjects with callosotomy indicate that the integrity of the corpus callosum is not indispensable for preservation of sound-lateralization ability. On the other hand, transcallosal interhemispheric transfer of auditory information obviously plays a significant role in spatial hearing functions that depend on binaural cues. Moreover, these data are compatible with the general view of a dominance of the right cortical hemisphere in auditory space perception.

Acoustic Stimulation↗

PubMed2005

Processing of auditory spatial cues in human cortex: an fMRI study.

The issue of where in the human cortex coding of sound location is represented still is a matter of debate. It is unclear whether there are cortical areas that are specifically activated depending on the location of sound. Are identical or distinct cortical areas in one hemisphere involved in processing of sounds from the left and right? Also, the possibility has not been investigated so far that distinct areas have a preference for processing of central and eccentric sound locations. The present study focussed on these issues by using functional magnetic resonance imaging (fMRI). Activations evoked by left, right and central sounds were analysed separately, and contrasts were computed between these conditions. We did not find areas, which were involved in the processing of exclusively left, right or central sound positions. Large overlapping areas rather were observed for the three sound stimuli, located in the temporal, parietal and frontal cortices of both hemispheres. This result argues for the idea of a widely distributed bilateral network accessing an internal representation of the body to encode stimulus position in relation to the body median plane. However, two areas (right BA 40 and left BA 37) also were found to have preferences for sound position. In particular, BA 40 turned out to be significantly more activated by processing central positions, compared to eccentric stimuli. In line with previous findings on visual perception, the latter observation supports the assumption that the right inferior parietal cortex may be preferentially involved in the perception of central stimulus positions in relation to the body.

Acoustic Stimulation↗

PubMed2004

Auditory-visual temporal integration as a function of distance: no compensation for sound-transmission time in human perception.

In a psychophysical outdoor experiment with human subjects, the point of subjective simultaneity (PSS) of auditory and visual stimuli was measured for distances from 1 to 50 m. Repetitive sound and light pulses were presented with various stimulus-onset asynchronies, and subjects judged which modality came first. With increasing distance of the stimuli the PSS shifted in a linear relation toward delays of the light behind the sound. The slope of the regression line (3 ms/m) almost exactly corresponded to that of the temporal disparities resulting from the lower velocity of sound compared to light. These data refute the hypothesis proposed recently that there could be an 'implicit estimation' of sound-arrival time. The brain seems to eliminate such crossmodal temporal disparities by the integration of auditory and visual stimuli that fall into a time window, but not by specific compensatory processes that use an estimate of the sound delay.

Acoustic Stimulation↗

PubMed2004

Gender-specific hemispheric asymmetry in auditory space perception.

This study aimed to investigate gender-related functional asymmetries in monaural sound localization in the vertical plane. In a simple pointing task, right-handed subjects localized vertical positions of sound sources using only one ear. Results show that females were more precise when listening with the left ear, while males did better with the right. However, significant differences in monaural localization performance as a function of gender occurred exclusively when listening with the right ear, with males performing substantially more precisely than females. These findings suggest gender-related differences in the intrahemispheric functional organization of the left hemisphere for the processing of monaural spatial cues. It is proposed that the results may be related to the sexual dimorphism of the posterior parietal cortex, or planum temporale, both areas known to be involved in spatial auditory functions.

Acoustic Stimulation↗

PubMed2004

Sound lateralization in Parkinson's disease.

The symptoms primarily associated with Parkinson's disease (PD) are of a motor and cognitive nature, but sensory deficits may also be involved. Previous studies have reported disturbed spatial perception in visual and tactile tasks. We have investigated whether PD patients show deficits in auditory spatial perception. For this purpose, we employed a simple task involving left/right judgments about dichotic stimuli presented with various interaural time differences (ITD). The acuity of sound lateralization was significantly reduced in PD: the just noticeable difference (JND) in interaural time seen in PD patients was about twice that seen for age-matched healthy controls. We propose that this deficit may be related to a potential role of the basal ganglia in spatial hearing functions, as has been suggested by neurophysiological and neuroanatomical studies on animals.

Acoustic Stimulation↗

PubMed2004

Shift in sound localization induced by rTMS of the posterior parietal lobe.

Neuroimaging studies in human subjects and single-unit recordings in monkeys have suggested the primate posterior parietal cortex (PPC) to be involved in auditory space perception. Here we tested this hypothesis by combining repetitive focal transcranial magnetic stimulation (rTMS) of the right PPC with a task of pointing to free-field-sound stimuli. After a period of 15 min rTMS at 1Hz, subjects exhibited an overall signed error in pointing by 2.5 degrees, directed to the left and downward, with reference to a baseline condition with "sham rTMS". No effects of rTMS on the general precision of sound localization (unsigned errors) were found. Thus, low-frequency offline rTMS may have specifically affected neuronal circuits transforming auditory spatial coordinates in both azimuth and elevation. This is in accordance with the view that the PPC may represent a neural substrate of the perceptual stability in spatial hearing.

Acoustic Stimulation↗

PubMed2004

Representational momentum in spatial hearing.

The final position of a moving visual object usually appears to be displaced in the direction of motion. We investigated this phenomenon, termed representational momentum, in the auditory modality. In a dark anechoic environment, an acoustic target (continuous noise or noise pulses) moved from left to right or from right to left along the frontal horizontal plane. Listeners judged the final position of the target using a hand pointer. Target velocity was 8 degrees s(-1) or 16 degrees s(-1). Generally, the final target positions were localised as displaced in the direction of motion. With presentation of continuous noise, target velocity had a strong influence on mean displacement: displacements were stronger with lower velocity. No influence of sound velocity on displacement was found with motion of pulsed noise. Although these findings suggest that the underlying mechanisms may be different in the auditory and visual modality, the occurrence of displacements indicates that representational-momentum-like effects are not restricted to the visual modality, but may reflect a general phenomenon with judgments of dynamic events.

Acoustic Stimulation↗

PubMed2004

Is there a role of visual cortex in spatial hearing?

The integration of auditory and visual spatial information is an important prerequisite for accurate orientation in the environment. However, while visual spatial information is based on retinal coordinates, the auditory system receives information on sound location in relation to the head. Thus, any deviation of the eyes from a central position results in a divergence between the retinal visual and the head-centred auditory coordinates. It has been suggested that this divergence is compensated for by a neural coordinate transformation, using a signal of eye-in-head position. Using functional magnetic resonance imaging, we investigated which cortical areas of the human brain participate in such auditory-visual coordinate transformations. Sounds were produced with different interaural level differences, leading to left, right or central intracranial percepts, while subjects directed their gaze to visual targets presented to the left, to the right or straight ahead. When gaze was to the left or right, we found the primary visual cortex (V1/V2) activated in both hemispheres. The occipital activation did not occur with sound lateralization per se, but was found exclusively in combination with eccentric eye positions. This result suggests a relation of neural processing in the visual cortex and the transformation of auditory spatial coordinates responsible for maintaining the perceptual alignment of audition and vision with changes in gaze direction.

Acoustic Stimulation↗

PubMed2004

Involvement of the superior temporal cortex and the occipital cortex in spatial hearing: evidence from repetitive transcranial magnetic stimulation.

The processing of auditory spatial information in cortical areas of the human brain outside of the primary auditory cortex remains poorly understood. Here we investigated the role of the superior temporal gyrus (STG) and the occipital cortex (OC) in spatial hearing using repetitive transcranial magnetic stimulation (rTMS). The right STG is known to be of crucial importance for visual spatial awareness, and has been suggested to be involved in auditory spatial perception. We found that rTMS of the right STG induced a systematic error in the perception of interaural time differences (a primary cue for sound localization in the azimuthal plane). This is in accordance with the recent view, based on both neurophysiological data obtained in monkeys and human neuroimaging studies, that information on sound location is processed within a dorsolateral "where" stream including the caudal STG. A similar, but opposite, auditory shift was obtained after rTMS of secondary visual areas of the right OC. Processing of auditory information in the OC has previously been shown to exist only in blind persons. Thus, the latter finding provides the first evidence of an involvement of the visual cortex in spatial hearing in sighted human subjects, and suggests a close interconnection of the neural representation of auditory and visual space. Because rTMS induced systematic shifts in auditory lateralization, but not a general deterioration, we propose that rTMS of STG or OC specifically affected neuronal circuits transforming auditory spatial coordinates in order to maintain alignment with vision.

Acoustic Stimulation↗

PubMed2003

Disturbed sound lateralization in patients with spatial neglect.

Previous studies on auditory space perception in patients with neglect have investigated localization of free-field-sound stimuli or lateralization of dichotic stimuli that are perceived intracranially. Since those studies in part revealed contradictory results, reporting either systematic errors to the left or systematic errors to the right, we reassessed the ability of auditory lateralization in patients with right hemispheric lesions with and without neglect. Unexpectedly, about half of the patients with neglect showed erratic judgments on sound position, that is, they were completely unable to lateralize sounds. The remaining neglect patients only showed a small deviation of the auditory median plane to the left side, indicating that they perceived the sounds as slightly shifted to the right side. The comparison between both groups revealed higher severity of neglect in the group of neglect patients who were unable to perform the task, suggesting that the inability of sound lateralization was associated with the strength of clinical neglect. However, we also observed 1 out of 9 patients with left brain damage who was not able to lateralize spatial sounds. This patient did not show any symptoms of spatial neglect. Thus, it may be that a spatial auditory deficit, such as that observed here in right-brain-damaged patients, only co-occurs with spatial neglect if the right superior temporal cortex is lesioned.

Adult↗

PubMed2003

Cross-modal perceptual integration of spatially and temporally disparate auditory and visual stimuli.

Under certain conditions, auditory and visual information are integrated into a single unified percept even when they originate in different locations in space. The present study shows how this illusion, known as the ventriloquism effect, depends on spatial, temporal and cognitive factors. A method of psychophysical scaling was employed in combination with simple auditory-visual stimuli (tone bursts and flashing light spots) that were presented with various spatiotemporal disparities. Participants either judged their impression of the likelihood of a common cause (Experiment 1) or spatial alignment (Experiment 2) or synchrony of sound and light (Experiment 3). In all three experiments the participants' judgements depended significantly on temporal disparity whereas influences of spatial disparity were significant in Experiments 1 and 2. Optimum scores were always obtained when auditory stimuli were presented with a delay of 50-100 ms after the visual stimuli. These results demonstrate that both temporal and spatial proximity of the two stimuli are critical for the experience of phenomenal causality. On the other hand, spatio-temporal ranges for optimal perception of phenomenal causality in Experiment 1 were significantly larger than predicted by simultaneous detection of spatial and temporal disparities. This finding suggests that auditory-visual binding was further facilitated by additional, cognitive, factors, associated with the specific instruction to judge the likelihood of a common cause. Obviously, these instructional influences may reflect similar perceptual effects, as have been shown previously by increasing the complexity or cognitive compellingness of auditory-visual stimuli.

Acoustic Stimulation↗

PubMed2002

Role of the posterior parietal cortex in spatial hearing.

The human posterior parietal cortex (PPC) is well known to be involved in various functions of multisensory spatial perception. However, the specific role of the PPC in hearing has, up to now, remained unclear. To allow more reliable conclusions to be drawn on this issue, we have used repetitive transcranial magnetic stimulation in healthy subjects. Focal stimulation of the PPC induced a systematic shift in the lateralization of interaural time differences (ITDs, a main cue for auditory azimuth), whereas the acuity of ITD discrimination was unaffected. We propose that the PPC is specifically involved in relating azimuthal angles of sound to the body coordinates and is part of a "where" stream in cortical processing of auditory information.

Acoustic Stimulation↗

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↗

PubMed2002

Vertical sound localization in blind humans.

It is widely held that early-blind people compensate their visual loss by a general sharpening of spatial hearing. The present study reports a possible exception to this view: when the vertical position (elevation) of a sound source had to be localized, four out of six early-blind subjects exhibited systematic deviations in pointing, while two early-blind subjects were as accurate as sighted controls. On the other hand, blind and sighted individuals were able to judge relative positions of different sound locations with similar precision. These results suggest that visual experience may be used to accurately calibrate the relation between the vertical coordinates of auditory space and body, but is not needed to develop sufficiently high resolution of spatial hearing.

Adult↗

PubMed2002

Opposing effects of head position on sound localization in blind and sighted human subjects.

Up to now, there is an unsolved contradiction between the view that the development of an auditory spatial representation needs calibration by vision and the psychophysical demonstration of quite precise sound localization in early blind humans. The present study provides a link between these two competing conceptions. Two experiments were conducted with congenitally or early blind subjects and sighted controls. In the first experiment, subjects pointed with their head to actual sound sources located in the azimuthal plane. In the second experiment, lateralization of dichotic sound stimuli, presented via headphones, was investigated with variation of head-to-trunk position. The results showed opposing systematic errors of sound localization or lateralization, depending on head position, made by blind and sighted subjects. These differences suggest that audiomotor feedback replaces vision so as to calibrate auditory space in blind individuals. That is, in contrast to the widespread opinion of compensation of visual loss by a general sharpening of audition, compensatory plasticity in the blind may specifically be related to enhanced processing of proprioceptive and vestibular information with the auditory spatial input.

Adaptation, Physiological↗