A continuous tracking measure of orientation sensitivity and bias in the visual periphery

Visual performance varies significantly across the visual field, revealing variations in sensitivity at different locations within and across observers. These include polar angle asymmetries—variations in performance across angular locations. Conventional methods for measuring these variations are time consuming but can be made more efficient with recent continuous tracking methods, in which observers follow a continuously changing target. This method calculates the peak of the cross-correlation between the tracked and reference stimuli, effectively assessing sensitivity. However, it does not directly quantify perceptual bias, which reflects systematic errors in perception. To address this, we introduce a novel approach to simultaneously map bias and sensitivity in orientation perception across the visual field at 8º eccentricity across four locations (upper, lower, right, and left). Participants fixate a central grating and adjust its orientation to match the orientation of a randomly rotating peripheral grating. We measured perceptual sensitivity by calculating the peak of the cross-correlation between the central and peripheral gratings. In addition, we measured bias by calculating the difference between observed and actual orientation values at each orientation, which are then grouped and averaged. To validate this approach, participants completed a second condition, in which we used the tilt illusion to measure biases in perceived orientation with a 45º annular surround for the peripheral grating. We reveal significant variations in the strength of the tilt illusion among participants and locations. Additionally, participants demonstrated significant variation in location-specific sensitivity in tracking the grating, both with and without the annulus in the periphery. Sensitivity was well correlated between the two tasks (p < .001), but lower with a surrounding annulus. Our results highlight individual differences in sensitivity and bias across the visual field with our novel continuous tracking paradigm, and variation in the magnitude of the tilt illusion in different peripheral field locations.