Showing papers by "Notger G. Müller published in 2007"

Object Familiarity and Semantic Congruency Modulate Responses in Cortical Audiovisual Integration Areas

Abstract: The cortical integration of auditory and visual features is crucial for efficient object recognition. Previous studies have shown that audiovisual (AV) integration is affected by where and when auditory and visual features occur. However, because relatively little is known about the impact of what is integrated, we here investigated the impact of semantic congruency and object familiarity on the neural correlates of AV integration. We used functional magnetic resonance imaging to identify regions involved in the integration of both (congruent and incongruent) familiar animal sounds and images and of arbitrary combinations of unfamiliar artificial sounds and object images. Unfamiliar object images and sounds were integrated in the inferior frontal cortex (IFC), possibly reflecting learning of novel AV associations. Integration of familiar, but semantically incongruent combinations also correlated with IFC activation and additionally involved the posterior superior temporal sulcus (pSTS). For highly familiar semantically congruent AV pairings, we again found AV integration effects in pSTS and additionally in superior temporal gyrus. These findings demonstrate that the neural correlates of object-related AV integration reflect both semantic congruency and familiarity of the integrated sounds and images.

Temporal Dynamics of the Attentional Spotlight: Neuronal Correlates of Attentional Capture and Inhibition of Return in Early Visual Cortex

Abstract: A stimulus that suddenly appears in the corner of the eye inevitably captures our attention, and this in turn leads to faster detection of a second stimulus presented at the same position shortly thereafter. After about 250 msec, however, this effect reverses and the second stimulus is detected faster when it appears far away from the first. Here, we report a potential physiological correlate of this time-dependent attentional facilitation and inhibition. We measured the activity in visual cortex representations of the second (target) stimulus' location depending on the stimulus onset asynchrony (SOA) and spatial distance that separated the target from the preceding cue stimulus. At an SOA of 100 msec, the target yielded larger responses when it was presented near to than far away from the cue. At an SOA of 850 msec, however, the response to the target was more pronounced when it appeared far away from the cue. Our data show how the neural substrate of visual orienting is guided by immediately preceding sensory experience and how a fast-reacting brain system modulates sensory processing by briefly increasing and subsequently decreasing responsiveness in parts of the visual cortex. We propose these activity modulations as the neural correlate of the sequence of perceptual facilitation and inhibition after attentional capture.

Competing neural responses for auditory and visual decisions.

Abstract: Why is it hard to divide attention between dissimilar activities, such as reading and listening to a conversation? We used functional magnetic resonance imaging (fMRI) to study interference between simple auditory and visual decisions, independently of motor competition. Overlapping activity for auditory and visual tasks performed in isolation was found in lateral prefrontal regions, middle temporal cortex and parietal cortex. When the visual stimulus occurred during the processing of the tone, its activation in prefrontal and middle temporal cortex was suppressed. Additionally, reduced activity was seen in modality-specific visual cortex. These results paralleled impaired awareness of the visual event. Even without competing motor responses, a simple auditory decision interferes with visual processing on different neural levels, including prefrontal cortex, middle temporal cortex and visual regions.