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Seminar Details

Date 28-5-2010
Time 11:00
Room/Location DISI-Sala Conferenze 3 piano
Title Neurons in the supragranular layers of monkey area V1 compensate receptive field shifts due to ocul
Speaker Dott. Nabil Daddaoua
Affiliation Department of cognitive neurology Hertie institute for clinical brain research Otfried Müller strass
Link http://www.hih-tuebingen.de/
Abstract We perceive the world as stable and upright despite ego motion. To construct a world-centered percept of our visual environment our visual system must compensate for the orientation of the eyes in the head and of the head in space. Previous work has suggested that the construction of such a world- centered representation is accomplished at later stages in the cortical processing of visual information, building on a fully retinal representation of the visual world in striate visual cortex (V1). Contrary to this widely held belief, we demonstrate that subsets of V1 neurons use information about eye torsion to keep receptive fields stable relative to the head despite tilt- induced ocular counter roll. This conclusion is based on the analysis of 89 neurons recorded from V1 layers 2-4 of a behaving monkey whose receptive fields were compared with the monkey´s head and body kept in different roll orientations. We obtained high-resolution receptive field maps using the reverse correlation technique while the monkey was actively fixating a target located in the middle of a computer screen. We repeated the same procedure with the monkey and the monitor presenting the stimuli roll tilted by 50deg and, finally, repeated the same procedure when the monkey was rolled back to the upright position. 2-D eye position was monitored using the search-coil technique and eye torsion was measured by means of a camera system. Roll- tilting the monkey by 50deg induced 4 to 5deg of ocular counter roll. 88% of neurons showed a shift of their receptive field location on the monitor, suggesting that they were not able to compensate for ocular counter roll. However, to our surprise, the remaining 12% exhibited receptive fields that did not shift on the monitor despite tilt-induced counter roll. In other words, they were head-centered. Head centered neurons were mostly located in the superficial layers 2 (3 of 39) and 3 (7 of 32) whereas 17 of 18 layer 4 neurons showed significant receptive field shifts, i.e. they were not head-centered. This layer-specific distribution of coordinate frame preferences suggests that non-retinal information on eye torsion is used to convert retinocentric signals in the major recipient of geniculate input, layer 4, into a head- centered format in supragranular primary visual cortex. On the other hand, the lack of any evidence for world-centered responses in V1 suggests that the integration of information about head orientation, requiring vestibular input, is reserved to extrastriate visual cortex. In other words, the construction of a world-centered representation of the perceptual visual world seems to take place in at least two steps associated with distinct parts of visual cortex.
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