![]() ![]() Inspired by these findings, we then conducted new fMRI scanning experiments of subjects instructed to attend to different regions of naturalistic scenes while fixating. This process of subjective analysis led to unexpected observations which were tested quantitatively, yielding a more complete view of the dataset than achieved by the original two studies. In interpreting these data-based RP-images, it was found helpful for comparison to employ retinotopic projection to visualize the output of a simple computational model of visual processing (i.e., to yield model-based RP-images). A comprehensive assessment of the dataset thus requires looking at brain responses to each stimulus photo and asking, what can be learned about visual processing? Viewing brain responses in the form of retinotopic projection images (RP-images) makes this task tractable. ( 2009) are, by their nature, not easily parametrized. The diverse stimulus photos of real scenes used in the studies of Kay et al. Together the results suggest that even during passive viewing, the visual system differentially processes natural scenes in a manner consistent with deployment of visual attention to salient elements. Retinotopic projection applied to these data showed that attending to an object increased activation in cortex corresponding to the location of that object. Next, in new fMRI experiments, three subjects directed attention toward various elements of naturalistic scenes (Vermeer paintings). However, consistent discrepancies were discovered: Human faces tend to evoke stronger responses relative to other scene elements than predicted by the model, whereas periodic patterns evoke weaker responses than predicted by the model. A simple model of local contrast integration accounts for much of the data in early visual areas (V1 and V2). Retinotopic projection is here first applied to a previously acquired fMRI dataset in which a large set of grayscale photos of real scenes were presented to three subjects. To view brain activity in register with visual stimuli, a technique here referred to as “retinotopic projection,” which translates functional measurements into retinotopic space, is employed. ![]()
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