The Impact of Affect on Neural Mechanisms Underlying Orientation Perception

The Impact of Affect on Neural Mechanisms Underlying Orientation Perception by Michelle L. Fowler Advisor: Andrea Li, PhD The underlying mechanisms used to process 2D visual information to form a unified 3D percept of the world remain largely unknown. Previous work in our lab has shown that accurate 3D perception of textured surfaces depends on the presence of specific patterns of orientation flows in the retinal image. Recent research has shown that affective state may influence the visual perception of oriented patterns. Relative to neutral face stimuli, fearful face stimuli have been shown to increase sensitivity to orientation of low spatial frequency patterns and decrease sensitivity to orientation of high spatial frequency patterns. How affective state influences the perception of orientation as used in more complex patterns and in patterns that convey 3D shape, which is processed higher in the visual pathway, is currently not known. Using the Radboud face database, we examined the effects of affective fear versus neutral face primes on orientation sensitivity using grating and plaid stimuli of low (2cpd) and high (4cpd) spatial frequency, and on 3D curvature sensitivity using images of 3D surfaces textured with 2cpd and 4cpd gratings. In Experiment One, we examined the role of fear on 2D orientation sensitivity of tilted gratings and plaid stimuli at both low and high spatial frequencies. Results replicated previous research showing increased orientation sensitivity to low frequency patterns and decreased orientation sensitivity to high frequency patterns; however, our results limit this finding as orientationspecific to vertically oriented stimuli only. Therefore, differences in tilt thresholds for spatial v frequency were shown to be dependent on orientation information contained within the pattern. In Experiment Two, we investigated the role of fear on 3D shape perception for surfaces slanted and corrugated in depth patterned with low and high frequency gratings. Results indicate that differences in the affective influence of orientation sensitivity for each spatial frequency were specific to processing area along the visual pathway. For 2D images conveying 3D shape, fear diminished, rather than increased, sensitivity for the low spatial frequency condition. However, for slanted surfaces, results indicated affective influence per spatial frequency for direction of slant. For corrugated surfaces, affective influence was found to be orientation specific for vertically corrugated stimuli patterned with horizontal gratings but was not found to have differential effects on spatial frequency. Therefore, affect may differentially influence visual processing of spatial frequency on orientation at multiple areas along the pathway. In Experiment Three, we assessed the contributions of the presence of a face prime, paradigm, and ordering effects on our results from Experiment One. Results confirm the robust nature of the affective influence of fear on the relationship between spatial frequency and orientation, as differences were not shown to be a result of no face primes, paradigm differences, or ordering effects. Taken together, our results indicate that the top-down modulation of affect differentially influences the saliency of spatial frequency information for orientation processing differently along multiple areas of the visual pathway.