Biomedical subjects

Rudy Guyonneau

Publications and source records attributed to Rudy Guyonneau.

4 recordsLinked to original sources

PubMed2006

Animals roll around the clock: the rotation invariance of ultrarapid visual processing.

The processing required to categorize faces and animals is not only rapid but also remarkably resistant to inversion. It has been suggested that this sort of categorization performance could be achieved using the global distribution of orientations within the image, which interestingly is unchanged by inversion. Here, we presented subjects with two natural scenes at 16 different orientations that were simultaneously flashed in the left and right hemifield and we asked them to make a saccade to the side containing an animal. We report that human performance is surprisingly rotation invariant as reaction times were similar and accuracy remarkably stable across orientations. The results imply that this form of rapid object detection could not depend on the global distribution of orientations within the image. One alternative is that subjects are instead using local combinations of features that are diagnostic for the presence of an animal.

Adult↗

PubMed2005

Temporal codes and sparse representations: a key to understanding rapid processing in the visual system.

Where neural information processing is concerned, there is no debate about the fact that spikes are the basic currency for transmitting information between neurons. How the brain actually uses them to encode information remains more controversial. It is commonly assumed that neuronal firing rate is the key variable, but the speed with which images can be analysed by the visual system poses a major challenge for rate-based approaches. We will thus expose here the possibility that the brain makes use of the spatio-temporal structure of spike patterns to encode information. We then consider how such rapid selective neural responses can be generated rapidly through spike-timing-dependent plasticity (STDP) and how these selectivities can be used for visual representation and recognition. Finally, we show how temporal codes and sparse representations may very well arise one from another and explain some of the remarkable features of processing in the visual system.

Action Potentials↗

PubMed2005

Spike times make sense.

Many behavioral responses are completed too quickly for the underlying sensory processes to rely on estimation of neural firing rates over extended time windows. Theoretically, first-spike times could underlie such rapid responses, but direct evidence has been lacking. Such evidence has now been uncovered in the human somatosensory system. We discuss these findings and their potential generalization to other sensory modalities, and we consider some future challenges for the neuroscientific community.

Action Potentials↗

PubMed2005

Neurons tune to the earliest spikes through STDP.

Spike timing-dependent plasticity (STDP) is a learning rule that modifies the strength of a neuron's synapses as a function of the precise temporal relations between input and output spikes. In many brains areas, temporal aspects of spike trains have been found to be highly reproducible. How will STDP affect a neuron's behavior when it is repeatedly presented with the same input spike pattern? We show in this theoretical study that repeated inputs systematically lead to a shaping of the neuron's selectivity, emphasizing its very first input spikes, while steadily decreasing the postsynaptic response latency. This was obtained under various conditions of background noise, and even under conditions where spiking latencies and firing rates, or synchrony, provided conflicting informations. The key role of first spikes demonstrated here provides further support for models using a single wave of spikes to implement rapid neural processing.

Action Potentials↗