Biomedical subjects

Notger G Müller

Publications and source records attributed to Notger G Müller.

10 recordsLinked to original sources

PubMed2006

Cross-modal processing in early visual and auditory cortices depends on expected statistical relationship of multisensory information.

Previous studies have shown that processing information in one sensory modality can either be enhanced or attenuated by concurrent stimulation of another modality. Here, we reconcile these apparently contradictory results by showing that the sign of cross-modal interactions depends on whether the content of two modalities is associated or not. When concurrently presented auditory and visual stimuli are paired by chance, cue-induced preparatory neural activity is strongly enhanced in the task-relevant sensory system and suppressed in the irrelevant system. Conversely, when information in the two modalities is reliably associated, activity is enhanced in both systems regardless of which modality is task relevant. Our findings illustrate an ecologically optimal flexibility of the neural mechanisms that govern multisensory processing: facilitation occurs when integration is expected, and suppression occurs when distraction is expected. Because thalamic structures were more active when the senses needed to operate separately, we propose them to serve gatekeeper functions in early cross-modal interactions.

Acoustic Stimulation↗

PubMed2005

Interactions between task difficulty and hemispheric distribution of attended locations: implications for the splitting attention debate.

Whether attention can be split between multiple regions in space simultaneously is an ongoing controversy in attention research. We argue that the debate could be resolved if the distribution of target locations over hemifields and task difficulty are both considered. This premise was tested in five experiments in which 48 subjects compared the identity of two out of four stimuli. In an easy task, within each hemifield, performance (reaction times and error rates) was better for adjacent targets than for separated ones, but across hemifields, performance for separated and adjacent stimuli was similar. In difficult tasks, performance was always better when the stimuli were presented across the hemifields indicating a bilateral field advantage. Moreover, the difference between adjacent and separate conditions within one hemifield diminished with increasing task difficulty. We propose a modified model of visuo-spatial attention, which permits the hemispheres to maintain and control simultaneous attentional foci.

Adult↗

PubMed2004

The attentional field has a Mexican hat distribution.

We assessed the interference by distracter letters on target discrimination as a function of the distance between incompatible distracters and target. The slope of the response time-distance function supports a Mexican hat pattern of attentional modulation in the visual field. We relate the results to our recent finding of neural activity suppression in primary visual cortex coding locations in the vicinity of an attended region [Muller, N. G., & Kleinschmidt, A. (2004). The attentional 'spotlight's' penumbra: Center-surround modulation in striate cortex. Neuroreport, 15(6), 977-980]. As behavioral performance parallels activity modulation of primary visual cortex but not other areas we propose that perceptual capacities are determined by attentional response properties of V1.

Adult↗

PubMed2004

The attentional 'spotlight's' penumbra: center-surround modulation in striate cortex.

By enhancing neural activity in respective retinotopic cortical representations attention increases the efficiency with which visual information at a selected location is processed. Behavioral data also suggest that information from the vicinity of the attended region is actively suppressed. In search for a physiological correlate of this 'spotlight's penumbra' we assessed neural responses in retinotopic representations of an attended location and of locations at different distances to it. Relative to passive viewing we found suppressed striate activity for the nearby but not for the far locations. This attention-driven center-surround distribution of neural activity may enhance the contrast between attended and non-attended objects. We relate the different behavior of extrastriate areas to their lower spatial resolution, i.e. larger receptive fields.

Adult↗

PubMed2003

Dynamic interaction of object- and space-based attention in retinotopic visual areas.

We investigated the interaction between object- and space-based attention by measuring activity in early visual cortex. After central cueing, when subjects directed attention to a spatially defined part of an object, activity in early visual areas was enhanced at corresponding retinotopic representations but also at representations of other locations covered by the object. Different from the assumption of automatic attentional "spreading" within an object, however, activity was greater for representations of cued than of uncued locations on the same object. These findings support an interaction of object-based spatial selection with object-independent spatial mechanisms in directing attention. When the target stimulus did not appear at the expected location, we found higher activation in areas representing other locations on the same object than equidistant locations on other objects. Objects, hence, also guide spatial search, and this may account for the behaviorally observed delay in processing parts of an unattended object.

Adult↗

PubMed2003

A physiological correlate of the "Zoom Lens" of visual attention.

Attending a certain region in space enhances activity in visual areas retinotopically mapped to this region; stimuli presented in this region are preferentially processed. The zoom lens model of visual attention proposes that the attended region can be adjusted in size and predicts a tradeoff between its size and processing efficiency because of limited processing capacities. By means of event-related functional magnetic resonance imaging, we analyzed neural activity in multiple visual areas as a function of the size of an attended visual field region, which was defined by a spatial cue stimulus. After cueing, a target object, defined by a specific feature conjunction, had to be identified among objects within the cued region. Neural activity preceding the objects in multiple retinotopic visual areas correlated with the size of the attended region, as did subjects' performance. While the extent of activated retinotopic visual cortex increased with the size of the attended region, the level of neural activity in a given subregion decreased. These findings are consistent with the physiological predictions of the zoom lens model. Size-related modulations of neural activity were pronounced in early visual areas. We relate this finding to the small receptive field of these areas, whereby only neuronal units with receptive fields covering the attended region received a top-down bias. This preactivation of neuronal units may then have gated selective processing of the features of the object that appeared at the attended location, thus enabling feature integration and object identification.

Adult↗

PubMed2003

The functional neuroanatomy of visual conjunction search: a parametric fMRI study.

Visual conjunction search is proposed to be a multicomponent process which involves scaling and successive shifts of attention in space as well as object identification. Here, we first mapped brain areas sustaining the proposed attentional subprocesses and then tested whether their activity was modulated by search load, i.e., the number of shifts, as predicted by serial search models. Search load was manipulated indirectly by precueing a varying number of locations at which relevant objects were shown. Multiple subregions within the intraparietal sulcus (IPS) and the prefrontal cortex were activated after cueing. Activity in the right posterior IPS was modulated by the distance of attention shifts and in the left posterior IPS by "zooming out" to cover a large region of the visual field. More anterior subregions of the left IPS responded to object identification irrespective of the need for serial scanning. Corresponding regions in the right IPS were modulated parametrically with respect to search load, along with the right temporoparietal junction. These results support a functional segregation of subregions of the IPS. The posterior regions participate in large-scale shifts and scaling of the attentional focus and the anterior regions in object identification and rapid serial shifts during search. The sustained activation in the frontal eye fields after cueing suggests a role in maintaining attention in the periphery. Together with the findings in early visual areas from this experiment (Müller et al., 2003) the current observations are best accounted for by hybrid models of visual conjunction search, where parallel processing in visual and temporoparietal regions and serial scanning controlled by the right IPS cooperate.

Adult↗

PubMed2002

Contributions of subregions of the prefrontal cortex to working memory: evidence from brain lesions in humans.

We investigated working memory in patients with focal brain damage involving subregions of the prefrontal cortex (PFC). Lesions in the dorsal portion of lateral PFC or the ventromedial portion of orbital PFC did not impair performance in tasks that required maintenance and monitoring of object or spatial information. Larger lesions involving both ventral and dorsal parts of the lateral PFC impaired maintenance and monitoring of spatial and object information, with more severe deficits observed in the spatial tasks. The results support a distributed localization of function in lateral PFC during working memory.

Adult↗

PubMed2002

Age-related changes in fronto-parietal networks during spatial memory: an ERP study.

Spatial attention and memory were compared in young and old subjects using non-delayed and delayed matching-to-sample tests. Both young and older subjects revealed a right hemisphere superiority for spatial processing. Older subjects were as accurate as young controls in the non-delay task supporting preserved attention ability in this spatial task. However, older subjects were impaired at 3 s retention intervals supporting an encoding and/or retrieval deficit in spatial memory. Stimulus evaluation demands were highest in the non-delay task and younger subjects generated the largest posterior P3 in this condition plus an additional frontal P3. The frontal P3 was reduced in amplitude in the delay tasks in the young subjects. Retention of spatial information during the delay period was characterized by a negative slow wave maximal over Pz that predicted later memory performance and was enhanced in those subjects with high memory performance. Conversely, older subjects generated a frontal P3 in both delay and non-delay conditions and a reduced sustained posterior scalp negativity in some delay conditions. The results support age-related alterations in frontal-parietal networks during spatial memory.

Adolescent↗

PubMed2002

Interactions of focal cortical lesions with error processing: evidence from event-related brain potentials.

Electrophysiological and hemodynamic studies have suggested that structures in the vicinity of the anterior cingulate cortex are involved in performance monitoring, particularly in detection of errors. Bidirectional interactions between the frontomedian system involved in performance monitoring and the lateral prefrontal cortex as well as the orbitofrontal cortex have been proposed, but few studies have directly addressed this issue. The authors used a speeded flankers task to investigate error-related event-related potentials in 3 patient groups with different focal cortical lesions. Whereas bilateral frontopolar lesions involving the orbitofrontal cortex as well as temporal lesions did not alter the error-related negativity (ERN), lesions of the lateral frontal cortex resulted in an abolition of the ERN and in a reduction of the error positivity.

Brain↗