The cost of aiming for the best answers: Inconsistent perception

Abstract

The laws of physics and mathematics describe the world we live in as internally consistent. As these rules provide a very effective description, and our interaction with the world is also very effective, it seems self-evident that our perception follows these laws. As a result, when trying to explain imperfections in perception, we tend to impose consistency and introduce concepts such as deformations of visual space. In this review, we provide numerous examples that show that in many situations we perceive related attributes to have inconsistent values. We discuss how our tendency to assume consistency leads to erroneous conclusions on how we process sensory information. We propose that perception is not about creating a consistent internal representation of the outside world, but about answering specific questions about the outside world. As the information used to answer a question is specific for that question, this naturally leads to inconsistencies in perception and to an apparent dissociation between some perceptual judgments and related actions.

Keywords: Euclidean; haptics; human; illusion; multisensory; phenomenal space; space perception; vision.

FIGURE 1

Inconsistent perception of brightness (original by Edward H. Adelson), CC BY-SA 4.0. Square A on the checkerboard appears to be darker than square B. At the same time, the vertical uniform gray rectangle that touches the squares is equally dark as A, as well as equally dark as B.

FIGURE 2

Schematic representation of stimuli consisting of a Gaussian envelope enclosing a finer structure. (A) A Gabor patch consists of a modulation of luminance by a sinusoid multiplied by a Gaussian. If the phase of the sinusoid is changing, the whole patch seems to move. (B) Shepard tones can be constructed by taking an infinite number of pure tones that are an octave apart and modulating the sound pressure level by a Gaussian.

FIGURE 3

Inconsistency in the double drift illusion (see Supplementary Video 1). When fixating the dot on the left, the Gabor patch appears to move vertically, parallel to the red line. Despite continuing to move vertically, the Gabor appears to cross the red line when it is about halfway along its path. The movie is based on the stimulus used by Lisi and Cavanagh (2015), but with an additional vertical red line that reveals the inconsistency: a change in perceived relative position that is inconsistent with the perceived direction of motion.

FIGURE 4

Inconsistency between size and position in the Brentano version of the Müller-Lyer illusion. The three red lines are (and appear to be) equidistant, and are clearly aligned with the blue dots, which are thus also equidistant. Nevertheless, the green line connecting the two dots on the left seems longer than the black line connecting the dots on the right. When the orientation of the arrows is flipped (see Supplementary Video 2), the length of the green line appears to change, while the blue dots seem to remain static.

FIGURE 5

Inconsistency in perspective viewing. Drawing based on the photograph in Kappers and te Pas (2001). Despite seeing a ceiling consisting of aligned square tiles and seeing that the orange lines are diagonals of such square tiles, the orange lines do not appear to be parallel. The figure obviously shows a two-dimensional rendition; Kappers and te Pas reported that the effect was even stronger in an actual room: the physically parallel fluorescent tubes appeared visually extremely non-parallel.

FIGURE 6

How the Poggendorff illusion warps visual space. (A) The red and blue disks on the right are perceptually aligned with the lines with the same color on the left. The alignment is illusory, as they are not aligned. (B) The three purple disks are the intersections between the diagonals obtained by connecting each of the three red points on the upper line with the two blue points on the lower line that are farthest away. (C) If the manipulations in (A,B) would have resulted in a homogeneous space, the three purple disks should be aligned. The straight line shows they do not: the central disk is slightly below the straight line. This is obviously a consequence of the error we introduced in (A). We showed experimentally that if one constructs the three positions indicated by the purple disks perceptually, they are also not aligned (Smeets et al., 2009).

FIGURE 7

Schematic representation of an experiment showing an inconsistency in sensory alignment of the tips of invisible fingers. (A) The set-up used (Kuling et al., 2017). When the right index-finger feels as if it is at the location of a visual target (B), and the left finger feels as if it is at the same visual location (C), the two fingers in general do not feel aligned (D).

FIGURE 8

A sculpture by Brian MacKay and Ahmad Abas in East Perth, Western Australia from three different viewpoints. In the left image, the structure looks like a Penrose triangle. One perceives an impossible structure, despite the existence of a real structure that yields the same retinal stimulation. This figure is based on pictures by Bjørn Christian Tørrissen (CC BY-SA 3.0).