Biomedical subjects

Julien Besle

Publications and source records attributed to Julien Besle.

3 recordsLinked to original sources

PubMed2005

Is the auditory sensory memory sensitive to visual information?

The mismatch negativity (MMN) component of auditory event-related brain potentials can be used as a probe to study the representation of sounds in auditory sensory memory (ASM). Yet it has been shown that an auditory MMN can also be elicited by an illusory auditory deviance induced by visual changes. This suggests that some visual information may be encoded in ASM and is accessible to the auditory MMN process. It is not known, however, whether visual information affects ASM representation for any audiovisual event or whether this phenomenon is limited to specific domains in which strong audiovisual illusions occur. To highlight this issue, we have compared the topographies of MMNs elicited by non-speech audiovisual stimuli deviating from audiovisual standards on the visual, the auditory, or both dimensions. Contrary to what occurs with audiovisual illusions, each unimodal deviant elicited sensory-specific MMNs, and the MMN to audiovisual deviants included both sensory components. The visual MMN was, however, different from a genuine visual MMN obtained in a visual-only control oddball paradigm, suggesting that auditory and visual information interacts before the MMN process occurs. Furthermore, the MMN to audiovisual deviants was significantly different from the sum of the two sensory-specific MMNs, showing that the processes of visual and auditory change detection are not completely independent.

Acoustic Stimulation↗

PubMed2005

Task-dependent activation latency in human visual extrastriate cortex.

Event related potentials (ERPs) were recorded from subjects who had to perform either an identification task or a simple detection task on moving visual stimuli. Results showed that the amplitude of the so-called visual "N1" component was larger for identification than for mere detection, replicating previous data obtained with static stimuli. However, we also found that: (i) the onset, peak and offset latencies of the visual N1 to dynamic stimuli were significantly earlier in the detection task than in the identification task, and (ii) in both conditions, the coordinates of the equivalent current dipoles best explaining the visual N1 component were consistent with those of the human motion visual area MT+/V5 in the extrastriate cortex. Altogether, these results indicate that dynamic stimuli may activate (at least partly) different pathways and processes in extrastriate cortex according to the nature of the task required on these stimuli.

Adult↗

PubMed2004

Bimodal speech: early suppressive visual effects in human auditory cortex.

While everyone has experienced that seeing lip movements may improve speech perception, little is known about the neural mechanisms by which audiovisual speech information is combined. Event-related potentials (ERPs) were recorded while subjects performed an auditory recognition task among four different natural syllables randomly presented in the auditory (A), visual (V) or congruent bimodal (AV) condition. We found that: (i) bimodal syllables were identified more rapidly than auditory alone stimuli; (ii) this behavioural facilitation was associated with cross-modal [AV-(A+V)] ERP effects around 120-190 ms latency, expressed mainly as a decrease of unimodal N1 generator activities in the auditory cortex. This finding provides evidence for suppressive, speech-specific audiovisual integration mechanisms, which are likely to be related to the dominance of the auditory modality for speech perception. Furthermore, the latency of the effect indicates that integration operates at pre-representational stages of stimulus analysis, probably via feedback projections from visual and/or polymodal areas.

Acoustic Stimulation↗