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The role of attention and adaptation in shaping cortical representations and the perception of abrupt changes in the visual environment

dc.contributor.advisorTreue, Stefan Prof. Dr.
dc.contributor.authorMehrpour, Vahid
dc.titleThe role of attention and adaptation in shaping cortical representations and the perception of abrupt changes in the visual environmentde
dc.contributor.refereeTreue, Stefan Prof. Dr.
dc.description.abstractengThe visual system receives a wealth of visual information about objects with changing features in time. Attention is a mechanism allowing us to prioritize the processing of relevant information at the expense of other information. Most physiological research efforts have focused on the cortical processing of stimulus properties, which remain unchanged in time and its attentional modulation. Instead, this study systematically investigates the neuronal representation of change events and addresses, for the first time, how attention affects this representation. I did this in the context of visual motion processing in a well-studied visual motion area, MT that contains a high proportion of direction-selective cells with responses enhanced by attention. In this thesis, electrophysiological recordings from area MT in two monkeys performing a motion direction change detection task were analyzed. While the monkeys maintained their gaze on a fixation point, a static random dot pattern (RDP) was displayed either inside or outside the receptive field (RF) of the neuron under study, cueing an upcoming target location. Subsequently, two RDPs moving in one of 12 directions were simultaneously presented inside and outside the RF. At a random time after motion onset, the direction of target or distractor changed by 25 deg. The animals were rewarded for detecting a target direction change and ignoring similar changes in distractor. The data show that MT population response to motion (prior to direction change) is precise and attention enhances MT responses. Population responses around the direction change event indicate that distractor and target direction changes of 25 deg have MT representation of 31 deg and 39 deg, respectively. My finding demonstrates that a change in motion direction has an overestimated representation in MT and that this overestimation is almost twice as high for attended vs. unattended stimuli. Further analysis of the data shows that these observations cannot be simply explained by classical models of adaptation (fatigue-based models), but rather they might be accounted for by a modern normalization model of adaptation. Although the design of the electrophysiological task was not suitable to identify the source of adaptation in this study, several lines of evidence suggest that the effects induced by adaptation are mostly generated locally in MT. I conducted a human psychophysical study to examine the perception of direction change in a task, which was very similar to that of monkey electrophysiology. The results indicate that perceived direction change in human subjects was also overestimated by about 7 deg. The results of a second psychophysical experiment support the idea that there is a causal link between the overestimation of represented direction change in MT and the overestimation of perceived direction change. Overall, This thesis demonstrates that: (1) although MT representation of motion is precise, a change in motion direction is overestimated in MT, (2) visual attention not only modulates neuronal responses, but also further exaggerates the direction change overestimation in MT, (3) changes in neuronal responses following the unattended and attended direction changes can be understood in the framework of motion adaptation (prior to the direction change) and its attentional modulation. These changes cannot be explained by fatigue models of adaptation. In contrast, a normalization model of adaptation might capture the response changes induced by the direction change, (4) perception of direction change is overestimated, and that this is causally linked to the overestimation of represented direction change in
dc.contributor.coRefereeWörgötter, Florentin Prof. Dr.
dc.contributor.thirdRefereeGail, Alexander Prof. Dr.
dc.contributor.thirdRefereeWolf, Fred Prof. Dr.
dc.contributor.thirdRefereeScherberger, Hansjörg Prof. Dr.
dc.contributor.thirdRefereeGöpfert, Martin Prof. Dr.
dc.subject.engmonkey electrophysiologyde
dc.subject.engstimulus changede
dc.subject.engvisual motion direction changede
dc.subject.engtuned normalizationde
dc.subject.engvisual motionde
dc.subject.engmiddle temporal visual area (MT)de
dc.subject.enghuman psychophysicsde
dc.affiliation.instituteGöttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften (GGNB)de
dc.subject.gokfullBiologie (PPN619462639)de

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