Measurements of Malleable Visual Mechanisms Through High-resolution fMRI and Perceptual Learning

Abstract

For many decades, low-level properties of the visual system, like orientation selectivity, were considered stable. However, advances in methodologies and theoretical frameworks have challenged this belief; we now know that external and internal factors can influence many low-level visual properties. I conducted three separate studies that looked at different visual properties using both behavioral and high-resolution neuroimaging methods, focusing on mechanisms in the primary visual cortex.The first study explored laminar profiles of magnocellular and parvocellular pathways in human V1. This neuroimaging study used achromatic checkerboards with low spatial frequency and high temporal frequency to target the color-insensitive magnocellular pathway and chromatic checkerboards with higher spatial frequency and low temporal frequency to target the color-selective parvocellular pathway of V1. This work resulted in three main findings. First, responses driven by chromatic stimuli had a laminar profile biased towards superficial layers of V1, as compared to responses driven by achromatic stimuli. Second, we found a stronger preference for chromatic stimuli in parafoveal V1 compared with peripheral V1. Finally, we found alternating stimulus-selective bands stemming from the V1 border into V2 and V3. The second study explored the orientation dependence of neural activity in human V1. This study measured responses to stimuli at different orientations to capture the orientation-tuning properties of V1 both across cortical space and through cortical depth. This work resulted in two main findings. First, we validated previous work that orientation preference can be predicted by retinotopic location (i.e., radial bias). Second, we captured V weak orientation selectivity across all depths in cortex and attribute this finding to the fact that fMRI responses reflect neural activity averaged over a finite volume of cortex. The last study explored if temporal dynamics of sensory eye dominance could be altered using a perceptual learning technique. This study used orthogonal gratings during binocular rivalry to influence the temporal dynamics of sensory eye dominance through repeated training. Participants completed 12 days of a task meant to increase representation of one stimulus over the other. Temporal dynamics before and after training were compared. We found an increase in the total time participants spent seeing the grating from the trained eye and concluded that temporal dynamics can be changed through perceptual learning. However, this effect was relatively weak and varied in strength across participants.