Biomedical subjects

Ulrike Zimmer

Publications and source records attributed to Ulrike Zimmer.

4 recordsLinked to original sources

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

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↗

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↗

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↗