Presenter:  John Serences
Presentation type:  Symposium
Presentation date/time:  7/26  3:10-3:35
 
Multivariate fMRI Investigations of Attention and Perceptual Decision Making
 
John Serences, UC Irvine
 
Visual features can be grouped into superordinate categories such as motion or color, as well as subordinate categories such as a specific direction of motion. Traditionally, fMRI studies have been restricted to the superordinate level of analysis because the BOLD response is spatially imprecise with respect to the topology of subordinate-level selectivity within visual cortex. For example, a 180? array of motion-selective columns in area MT are contained within 0.5mm of cortex. Functional MRI voxels are large in comparison; however, if a preponderance of neurons preferring a particular feature are sampled within a voxel, then that voxel will exhibit a small feature-selective response bias. By considering the pattern of activity across many weakly selective voxels, it is possible to predict the feature that an observer is viewing. I describe two studies illustrating the utility of applying multivariate methods to the study of human perception and cognition. First, we predicted the attentional state of human observers as they monitored one of two overlapping directions of motion. Our analysis revealed that feature-specific attentional modulations spread to blank regions of the display, presumably increasing sensitivity to behaviorally relevant features across the visual field. In a second example, we show that the pattern of activation in nearly all visual areas discriminates the direction of a field of moving dots. However, some midlevel areas also discriminate the 'perceived' direction of motion even when presented with an ambiguous stimulus, suggesting that these regions support perception in the absence of sensory evidence.