Why Things Look Smaller in Your Peripheral Vision

For most people, the world is just as it appears to be. When we observe a complex scene, we have a sense that we see things as they are, with full sharpness, color, and resolution. However, the reality is that our visual field contains a highly distorted version of reality, where items in central vision are vibrantly colorful and detailed, and items in peripheral vision are colorless, dull, and blurry. We compensate for this by frequently moving our eyes around and capturing high-resolution details, one small region at a time. Our brains somehow manage to stitch together these partial, distorted images to construct a stable, continuous perceptual representation that allows us to interact with our environment.

One way in which our peripheral vision distorts reality is in the estimation of size. Because our brain dedicates so many resources to the center of our vision and so few resources to the periphery, our perception of size is not consistent across the visual field: Objects appear smaller in the periphery than in the center of our vision. This is known as the size-eccentricity effect and was first reported by Joseph Baldwin and colleagues in 2016. When participants judged the size of circles presented either in central or peripheral vision, they consistently underestimated the size of the peripheral circles. This size distortion effect is thought to be due to cortical magnification, the process by which the central region of our retina is mapped onto progressively larger regions in the brain as information flows up the visual pathway.

A new study published by Tristan Jurkiewicz and colleagues in this month's issue of Perception investigated whether the size-eccentricity effect is fixed, or whether it can be modulated by attention. In their study, participants judged which of two rectangles was thicker: one presented in the center of the visual field, and another flashed briefly in some location in the periphery. Before each trial, participants were cued with an arrow that reliably (but not perfectly) predicted the subsequent location of the peripheral rectangle. On 70 percent of the trials, the arrow cue was valid, meaning that the peripheral rectangle appeared where it was expected (e.g., a right-pointing arrow was followed by a rectangle flashed on the right side). In the remaining 30 percent of trials, the arrow cue was invalid, meaning that the subsequent peripheral rectangle appeared in the location opposite that indicated by the arrow.

Participants consistently underestimated the thickness of peripheral rectangles relative to the central rectangles, replicating the size-eccentricity effect. In fact, underestimation was more pronounced the farther the rectangles were located in peripheral vision. Intriguingly, this size bias was significantly diminished during valid trials compared to invalid trials. That is, when participants could correctly expect the location of the peripheral rectangle, their size underestimation bias became very weak. When the location of the peripheral rectangle was unexpected, the size underestimation bias was strong. These results based on participants' size judgments were corroborated by reaction time analyses that showed participants were significantly faster during valid than invalid trials, suggesting that the improved size accuracy during valid trials was not due to a speed-accuracy trade-off.

The findings by Jurkiewicz and colleagues suggest that the size-eccentricity bias is not entirely hardwired in the brain. Although our brains have hardwired physiology that produces cortical magnification, the fact that size judgments can be modulated by attention suggests that this bias is subject to top-down influences and processing priorities. When attention is deployed to a particular location in the visual field, it leads to improvements in perceptual processing that can (at least partially) compensate for our hardwired biases and distortions.