Contextual effects in the primary visual cortex of anesthetized cats.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2007)
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|Item Type:||Ph.D. Thesis|
|Title:||Contextual effects in the primary visual cortex of anesthetized cats|
Responses of visual cortical neurons in early processing stages can be modulated by stimuli presented outside the classical receptive field. The function of these context effects is still not completly understood, but its relevance for global image processing such as figure-ground segregation has been suggested. In the present study we investigate aspects of centre-surround interactions and the role of neural synchronisation in this context. Neuronal synchronization has been proposed to underlie the formation of neuronal assemblies and to possibly play a crucial role during the process of scene segmentation. We recorded multi-unit activity with up to 32 channels simultaneously from area 17 of anaesthetized cats. A sinusoidal drifting grating (figure) covering the receptive fields of the recorded neurons was made to perceptually pop out from a simultaneously presented background grating either by changing the relative orientation or by successively increasing the relative spatial phase between the two gratings. Altering the orientation contrast between centre and surround had no significant effect on synchronization strength. By contrast, firing rates showed showed a strong dependence on the relative orientation difference between the two gratings, showing strong suppression when figure and background were iso-oriented. This suppression progressively decreased as the orientation difference between figure and background increased. Changes in the relative spatial phase on the other hand had a significant effect on synchronisation strength. Synchronization strength increased when figure and background were segregated by an offset in the spatial phase and this increase was correlated with the gradual increase in relative spatial phase between figure and background. At the same time, long-distance synchronization between two groups of neurons stimulated by either figure or background decreased with increasing phase difference. Our results indicate that rate changes might play a role in segregating orientations while synchrony may be crucial in encoding phase differences. These findings suggest that firing rates and synchrony may represent two distinct and complementary mechanisms for the encoding of different aspects of contextual information and the grouping of responses and thus are a possible neurophysiological substrate of perceptual figure-ground segregation.
|Place of Publication:||Darmstadt|
|Uncontrolled Keywords:||visueller Kortex|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie|
|Divisions:||10 Department of Biology|
|Date Deposited:||17 Oct 2008 09:22|
|Last Modified:||07 Dec 2012 11:52|
|Referees:||Singer, Prof. Dr. Wolf and Thiel, Prof. Dr. Gerhard|
|Advisors:||Galuske, Prof. Dr. Ralf|
|Refereed:||18 December 2006|