An Adaptable Metric Shapes Perceptual Space

Abstract

SummaryHow do we derive a sense of the separation of points in the world within a space-variant visual system? Visual directions are thought to be coded directly by a process referred to as local sign, in which a neuron acts as a labeled line for the perceived direction associated with its activation [1, 2]. The separations of visual directions, however, are not given, nor are they directly related to the separations of signals on the receptive surface or in the brain, which are modified by retinal and cortical magnification, respectively [3]. To represent the separation of directions veridically, the corresponding neural signals need to be scaled in some way. We considered this scaling process may be influenced by adaptation. Here, we describe a novel adaptation paradigm, which can alter both apparent spatial separation and size. We measured the perceived separation of two dots and the size of geometric figures after adaptation to random dot patterns. We show that adapting to high-density texture not only increases the apparent sparseness (average element separation) of a lower-density pattern, as expected [4], but paradoxically, it reduces the apparent separation of dot pairs and induces apparent shrinkage of geometric form. This demonstrates for the first time a contrary linkage between perceived density and perceived extent. Separation and size appear to be expressed relative to a variable spatial metric whose properties, while not directly observable, are revealed by reductions in both apparent size and texture density.

Visual crowding is unaffected by adaptation-induced spatial compression

“…The spatial compression effect we report is also similar to that previously described by Hisakata et al ( 2016 ). In their original study, adaptation to an array of dots resulted in two dots presented subsequently in the adapted field to appear closer together.…”

“…In their original study, adaptation to an array of dots resulted in two dots presented subsequently in the adapted field to appear closer together. Hisakata and colleagues ( 2016 ) attribute their effects to changes in an internal spatial metric, against which judgments of local distance and size are made. However, in their experiments, the test patterns were located in the adapted area, were accompanied by a reduction in perceived texture density, and could occur in the absence of a contextual figural aftereffect.…”

“…In a recent study, Hisakata et al ( 2016 ) showed adaptation to a dense texture reduced the perceived separation of two subsequently presented dots. This spatial compression was present when the adapting texture encompassed the entire viewing field, ruling out the possibility that it could be caused by adaptation to the larger-sized adapting stimulus.…”

“… It has recently been shown that adapting to a densely textured stimulus alters the perception of visual space, such that the distance between two points subsequently presented in the adapted region appears reduced (Hisakata, Nishida, & Johnston, 2016 ). We asked whether this form of adaptation-induced spatial compression alters visual crowding.…”

Unifying Visual Space Across the Left and Right Hemifields

“…Eight subjects (3 female, including 1 author, and 5 male; age range: 20-32 years) took part in both Experiments 1a and 1b. The sample size we used is common for studies of visual adaptation and aftereffects (e.g., Hisakata, Nishida, & Johnston, 2016;Whitney, 2005;Wolfe, 1987). All experimental procedures were approved by the University of California (UC) Berkeley Institutional Review Board.…”