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Spatial, feature and temporal attentional mechanisms in visual motion processing

dc.contributor.advisorTreue, Stefan Prof.
dc.contributor.authorBaloni, Soniade
dc.titleSpatial, feature and temporal attentional mechanisms in visual motion processingde
dc.contributor.refereeGail, Alexander Prof.
dc.description.abstractengThe three projects documented in this thesis investigated the role of three forms of attention in visual processing. Spatial, feature-based and temporal attention. The spatial and feature-based attentional characteristics were studied by conducting extracellular recordings from neurons of area MT and MSTd of macaque visual cortex. While the role of temporal attention was studied in a human psychophysics project. In the physiology projects we first defined the tuning characteristics of neurons from area MT and MSTd for two stimulus dimensions, namely spiral motion stimuli (SMS) and linear motion stimuli (LMS) on the basis of directionality index, the relative frequency of tuned versus untuned neurons, and the individual cells responses to the two forms of stimuli. We found that MT and MSTd showed differential tuning to LMS and SMS. Area MSTd demonstrated better selectivity for SMS as compared to LMS. Conversely, area MT was better tuned to LMS than SMS. Further, we compared spatial and feature-based attentional modulation in area MT and MSTd across SMS and LMS. We found that spatial attention modulates the responses of neurons in both the areas irrespective of the feature dimension defining the attended stimuli. On the other hand feature-based attention was restricted to the stimulus dimension for which an area showed better selectivity, that is SMS for MSTd and LMS for MT. We also observed that the correlation of firing rates with reaction times was restricted to an area’s preferred stimulus dimension. The presence of a significant negative correlation of firing rate with reaction time in area MSTd when attention was directed to its preferred dimension (SMS), indicated that these neurons were involved in perceptual processing of SMS. Similarly, the presence of a significant negative correlation of firing rates with the reaction times in area MT when attention was directed to LMS, provides evidence that MT neurons were involved in perceptual processing of LMS. Taken together, these results show that neurons across the visual cortex are tuned to a range of stimulus dimensions. This multiple stimulus selectivity is thought to be utilized to develop a saliency map (by interaction of bottom-up and top-down processes), which marks the behaviorally relevant aspects of visual space. These behaviorally relevant aspects of the visual space are then preferentially processed throughout the visual hierarchy, and our results suggests that a given area contributes to visual perception by flexibly processing only the stimulus dimension for which it shows best selectivity as a function of stimulus relevance. Finally in human subjects we investigated the temporal characteristics of visual motion processing, using the ‘attentional blink’ paradigm. Attentional blink is a widely studied phenomenon, but almost all studies to the date have been are restricted to stationary stimuli. We here extended this paradigm to motion stimuli. We found the presence of an attentional blink in the motion domain, in that the detection of second of the two target (motion) stimuli was severely degraded when it was presented within 450ms of the first target (motion) stimulus. However, our results were slightly different from the experiments with the stationary stimuli. First, there was an absence of the lag-1 sparing effect typically found with stationary stimuli and second, the time interval over which the attentional blink was observed was about 100ms shorter than typically reported for stationary stimuli. Post-hoc analysis showed that these effects in the motion domain were dependent upon the direction of motion of the first target. Our data showed that when the first target moved in the opposite direction to the second target, there was no attentional blink, but when the first target moved in an orthogonal direction to the second target, there was an attentional blink. These results are in agreement to previous studies showing that the processing of motion stimuli is facilitated when it is preceded by a stimulus moving in opposite directions, while processing of motion stimuli is suppressed when it is preceded by a stimulus moving in an orthogonal direction. Taken together the results of this thesis provides an important contribution to our understanding of the role of attention in visual motion processing. It will be interesting to extend this study in other visual cortical areas and measure spatial and feature-based attention from same set of neurons across different stimulus
dc.contributor.coRefereeWolf, Fred Prof.
dc.contributor.thirdRefereeWilke, Melanie Prof.
dc.contributor.thirdRefereeMoser, Tobias Prof.
dc.contributor.thirdRefereeScherberger, Hansjörg
dc.subject.engVisual cotexde
dc.subject.engVisual motion processingde
dc.subject.engspatial attentionde
dc.subject.engFeature-based attentionde
dc.subject.engTemporal attentionde
dc.affiliation.instituteGöttinger Graduiertenschule für Neurowissenschaften, Biophysik und molekulare Biowissenschaften (GGNB)de
dc.subject.gokfullBiologie (PPN619462639)de

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