Retinal blur and the perception of egocentric distance

Abstract

A central function of vision is determining the layout and size of objects in the visual field, both of which require knowledge of egocentric distance (the distance of an object from the observer). A wide range of visual cues can reliably signal relative depth relations among objects, but retinal signals directly specifying distance to an object are limited. A potential source of distance information is the pattern of blurring on the retina, since nearer fixation generally produces larger gradients of blur on the extra-foveal retina. While prior studies implicated blur as only a qualitative cue for relative depth ordering, we find that retinal blur gradients can act as a quantitative cue to distance. Surfaces depicted with blur gradients were judged as significantly closer than those without, with the size of the effect modulated by the degree of blur, as well as the availability of other extra-retinal cues to distance. Blur gradients produced substantial changes in perceived distance regardless of relative depth relations of the surfaces indicated by other cues, suggesting that it operates as a robust cue to distance, consistent with the empirical relationship between blur and fixation distance.

Optimal defocus estimation in individual natural images

“…Thus, defocus information is nearly always present in images of natural scenes. Defocus information is vital for many natural tasks: depth and scale estimation (1,2), accommodation control (3,4), and eye growth regulation (5,6). However, little is known about the computations visual systems use to estimate defocus in images of natural scenes.…”

Depth perception with gaze-contingent depth of field

“…The overall pattern of blur created by DOF is a quantitative cue for perceived egocentric distance [32] and perceived size of objects [7]. The egocentric distance information provided by defocus blur may also serve to scale other depth cues [32].…”

“…The egocentric distance information provided by defocus blur may also serve to scale other depth cues [32]. Finally, blur can contribute to speed and accuracy in depth perception [20] and in some situations, blur differences between objects separated in depth are more discriminable than binocular disparity between them [6].…”

“…However, the introduction of the background factor corresponds to a less obvious goal. There is a running discussion in the blur perception literature regarding the nature of the type of information provided by defocus blur in natural perception (ordinal vs. quantitative) and whether the context blur of the field/scene provides valuable information [6,32]. Notice that an appropriately blurred background does contain information about the depth of an object (objects on focus are at the same depth than the parts of the background that is on focus).…”

“…This is due to the constrained depth of field of the human eye; objects appear more or less blurred depending on their position, and the position of the focal plane [11,25]. Blur patterns can affect the perceived distance between objects [19] and convey information about the distance of the focused object from the observer [32].…”