Spatial context in the early visual system

Important visual objects in our everyday life, such as fellow people, passing cars or birds perhaps, are not point-like structures but often occupy considerable amounts of the visual field. However, each photoreceptor in our eyes samples just a tiny portion of the visual field and somehow the visual system should integrate these local signals. This process takes place mainly in the visual cortex and, while higher-order visual areas play an important role in perception of extended structures, it is now well established that visual neurons at the first cortical steps of seeing integrate broad spatial context into their responses. The main purpose of this thesis was to provide detailed information concerning the spatial structure of the mechanisms that underlie integration of spatial context in the early visual system. The opening study of this thesis showed that the antagonistic Gaussians structure that has been used for modeling context integration in single visual neurons provides a relatively accurate description of the process also in the human visual system. The first study introduced a novel method for connecting perceptual and neuroimaging measurements and this method was applied in the second study of this thesis. The second study showed that the human visual system integrates spatial context in terms of its visual field size instead of the size of its cortical representation. The third study showed that context is integrated over an unexpectedly large region of the visual field and that spatially distant context may sometimes increase the contrast response of the visual system. The closing study showed that orientation specificity of the integration of spatial context depends on distance both in single neurons in the macaque primary visual cortex and in human perception. The knowledge acquired in this thesis will be generally useful in applications that require understanding of the human visual system.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2013

Author dc:creator

• Nurminen, Lauri

• psykologia

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/40213

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F40213