How the window of visibility varies around polar angle

Abstract

Contrast sensitivity, the amount of contrast required to detect or discriminate an object, depends on spatial frequency (SF): The Contrast Sensitivity Function (CSF) peaks at intermediate SFs and drops at lower and higher SFs and is the basis of computational models of visual object recognition. The CSF varies from foveal to peripheral vision, but only a couple studies have assessed changes around polar angle of the visual field. Sensitivity is generally better along the horizontal than the vertical meridian, and better at the lower vertical than the upper vertical meridian, yielding polar angle asymmetries. Here, we investigate CSF attributes at polar angle locations at both group and individual levels, using Hierarchical Bayesian Modeling. This method enables precise estimation of CSF parameters by decomposing the variability of the dataset into multiple levels and analyzing covariance across observers. At the group level, peak contrast sensitivity and corresponding spatial frequency with the highest sensitivity are higher at the horizontal than vertical meridian, and at the lower than upper vertical meridian. At an individual level, CSF attributes (e.g., maximum sensitivity, the most preferred SF) across locations are highly correlated, indicating that although the CSFs differ across locations, the CSF at one location is predictive of the CSF at another location. Within each location, the CSF attributes co-vary, indicating that CSFs across individuals vary in a consistent manner (e.g., as maximum sensitivity increases, wso does the SF at which sensitivity peaks), but more so at the horizontal than the vertical meridian locations. These results show similarities and uncover some critical polar angle differences across locations and individuals, suggesting that the CSF should not be generalized across iso-eccentric locations around the visual field. Our window of visibility varies with polar angle: It is enhanced and more consistent at the horizontal meridian. Author summary The contrast sensitivity function (CSF), depicting how our ability to perceive contrast depends on spatial frequency, characterizes our “window of visibility”: We can only see objects with contrast and spatial frequency properties encompassed by this function. The CSF is mostly assessed only along the horizontal meridian of the visual field and sometimes averaged across locations, but visual performance varies with polar angle (e.g., we are more sensitive to objects along the horizontal than the vertical meridian). Here, we systematically assess the key attributes of the CSF and show critical differences in the window of visibility across polar angles and individuals. We found that at the horizontal meridian, our overall contrast sensitivity and preferred SF are higher, and CSFs of individual observers co-vary more than at the vertical meridian. This research highlights that this fundamental perceptual measure is not the same and should be assessed around the visual field. Polar angle thus should be a key consideration for applications of the CSF in computational models of vision.