Visual environment is brimming with information, but human brain can only process limited amount of inputs at a time. This is because neural spiking is costly in energy consumption. Only a small portion of neurons can be active concurrently. Attention is a central cognitive and neural process that allows the brain to selectively process relevant inputs. In this dissertation, we investigate the role of attention in two perceptual phenomena: binocular rivalry and saccade preparation.
Part I, binocular rivalry: When the corresponding retinal locations in the two eyes are presented with incompatible images, a stable percept gives way to perceptual alternations in which the two images compete for perceptual dominance. Conventional computational models of rivalry propose that rivalry is mediated by mutual inhibition wired between two neural populations, and the perceptual dynamics of rivalry mainly depends on bottom-up inputs. However, converging behavioral and neuroimaging studies on human have found that rivalry relies on attention to persist. These findings require an update on the theory of binocular rivalry.
With a psychophysical experiment, we first found that the gain change of visual responses involved in binocular competition can be explained by a stimulus-driven attention that enhances the feature of the dominant image and suppresses the feature of the weaker image. Based on this notion, we proposed a new computational model of binocular rivalry. We showed that the model explains a wide range of key perceptual phenomena reported in rivalry. Finally a spatiotemporal version of the model predicts that attention slows down the speed of traveling waves in rivalry, consistent with a previous neuroimaging study. We conclude that attention plays a role that maintains and stabilizes dominant percept in rivalry, and our framework can be extended to study the dynamics of perception in the context other than binocular rivalry.
Part II, saccade preparation: When exploring visual scenes, human and primates perform large rapid eye movements–saccades–to bring objects of interest into the fovea. Behavioral performance (d' in visual discrimination tasks) for the saccade target is enhanced ∼100 ms before saccade onset. Although an improvement of performance provides evidence that extra-retinal signals evoked by saccades modulate visual perception, it remains unknown whether and how presaccadic attention changes the processing of featural information. In two psychophysical experiments, we first employed reverse correlation method and found that presaccadic attention sharpens orientation tuning and shifts the peak of spatial frequency (SF) tuning function toward higher frequencies. We then demonstrate that this enhancement (of high SF) is an inflexible process that occurs even when it could impair performance in a task. We suggest that the perceptual modulations by presaccadic attention we found may facilitate transaccadic integration by reshaping the representation of the saccade target to be more fovea-like before saccade onset. In addition, we suggest that future study should characterize and compare the perceptual modulations induced by covert spatial attention, presaccadic attention and saccade preparation.
|Advisor:||Heeger, David J., Carrasco, Marisa|
|Commitee:||Kiani, Roozbeh, Ma, Wei Ji, Rinzel, John|
|School:||New York University|
|School Location:||United States -- New York|
|Source:||DAI-B 80/07(E), Dissertation Abstracts International|
|Subjects:||Neurosciences, Psychology, Physiology, Physiological psychology|
|Keywords:||Attention, Binocular rivalry, Computational model, Dynamical system, Eye movement, Saccade|
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