Visual Field Asymmetries: The Effect of Configuration and Location

Performance in visual tasks is limited by the low-level mechanisms that sample the visual field. For many low-level visual tasks, performance decreases as a function of eccentricity; yet it also varies at isoeccentric locations: performance is better along the horizontal meridian than the vertical meridian, and along the lower than the upper vertical meridian. Crowding occurs when similar objects (“crowders”) flanking a target interfere with target discrimination. Crowding is considered a high-level phenomenon by many, thus is unclear whether visual field asymmetries will also be present for crowding, and whether or not the placement of the crowders would affect observed visual field asymmetries. In a visual discrimination task, a target was presented in eight isoeccentric locations across the visual field where crowding thresholds were measured for a variety of crowder configurations. Visual field asymmetries were measured in a novel way and modeled using an ellipse. Patterns of visual field asymmetries were observed for the crowding task, yet they also changed when crowder configuration was coded with respect to fixation, not the target. Crowders nearer fixation elicited less of an effect on crowding, yet the model overestimated performance at the upper vertical meridian and underestimated performance at the lower vertical meridian, despite equal performance between the respective adjacent locations. Crowders nearer the periphery presented an elliptical performance field despite large crowding thresholds: performance was correctly estimated and no performance deficit at the North location was observed. These results can be used to further understand how placement of non-critical features can affect a critical binding feature in perceptual grouping. This is useful in devising alternative therapies for patients who have lost use of their central vision.