Figure 3.

A potential role for the PLR in optimizing acuity in natural vision. (A) Natural scenes have luminance gradients, such that successive saccades can target regions with very different brightness (Image: Ansel Adams, “Acoma Pueblo. [National Historic Landmark, New Mexico],” U.S. National Archives, identifier #519836). (B) Cartoon illustrating how a tradeoff between signal to noise and optical aberrations could produce different optimal pupil sizes for different luminance regions. The effect of optical aberrations on vision (costs, solid blue line) increase as a function of pupil size. A larger pupil also increases the amount of light passing through, which means that the signal to noise ratio (SNR) would also increase as a function of pupil size, producing a decreasing cost for vision as a function of pupil size (solid gray and black lines). Because luminance varies across the scene, different regions would have different intrinsic signal levels, which would interact with pupil size to determine the costs (compare solid gray and black lines). To find the optimal pupil size across these two conditions, we can calculate the total costs due to both SNR and optical aberrations (dotted gray lines), then find the pupil size that minimizes these total costs (asterisks).