Foggy perception slows us down

Abstract

Visual speed is believed to be underestimated at low contrast, which has been proposed as an explanation of excessive driving speed in fog. Combining psychophysics measurements and driving simulation, we confirm that speed is underestimated when contrast is reduced uniformly for all objects of the visual scene independently of their distance from the viewer. However, we show that when contrast is reduced more for distant objects, as is the case in real fog, visual speed is actually overestimated, prompting drivers to decelerate. Using an artificial anti-fog—that is, fog characterized by better visibility for distant than for close objects, we demonstrate for the first time that perceived speed depends on the spatial distribution of contrast over the visual scene rather than the global level of contrast per se. Our results cast new light on how reduced visibility conditions affect perceived speed, providing important insight into the human visual system.DOI: http://dx.doi.org/10.7554/eLife.00031.001

Motion direction, luminance contrast, and speed perception: An unexpected meeting

“…Like directional anisotropies, the effect of luminance contrast on the perceived motion also received the attention of several studies in the last forty years (Blakemore & Snowden, 1999;Hassan & Hammett, 2015;Pretto et al, 2012;Stocker & Simoncelli, 2006;Thompson et al, 2006;Weiss et al, 2002). This phenomenon occurs with a variety of motion stimuli, including sine-wave gratings, random dot patterns, and discs (similar to those used in the present study).…”

“…Human observers take into account the effect of contrast attenuation due to particles in water in perceptual judgments. Due to water droplets in air, which is even augmented in fog, objects having lower luminance contrast are perceived as farther in space (O'Shea et al, 1994;Pretto et al, 2012). Observers consider the effects of a water medium on the deformation in shape of an object (Dövencioglu, van Doorn, Koenderink, & Doerschner, 2018), and take into account buoyancy to estimate object motion (Castillo, Waltzer, & Kloos, 2017;Masin & Rispoli, 2010).…”

“…In addition to the direction of motion and the representational gravity, luminance contrast also provides important information on object motion, depth, and shape (Adelson & Movshon, 1982;Kandel, 2012;O'Shea, Blackburn, & Ono, 1994). Due to the contrast attenuation by water droplets in air, which is even augmented in fog, objects having lower luminance contrast are perceived as farther in space (O'Shea et al, 1994;Pretto, Bresciani, Rainer, & Bülthoff, 2012). A change in stimulus contrast causes a bias in the perceived speed, which is perceived as slower at lower contrast (Thompson, 1982;Weiss, Simoncelli, & Adelson, 2002).…”

Systematic misperceptions of 3D motion explained by Bayesian inference

“…The errors predicted by the current model will no doubt be most apparent in the real world under demanding conditions, such as when there is limited time, or poor visibility (Pretto, Bresciani, Rainer, & Bülthoff, 2012;Shrivastava, Hayhoe, Pelz, & Mruczek, 2010;Snowden, Stimpson, & Ruddle, 1998). In situations where sensory uncertainty is very low, the model predicts that these perceptual errors will be negligible.…”

“…In the laboratory, a large number of studies have reported systematic biases in the perception of 3D motion, despite the availability of many such cues (Fulvio, Rosen, & Rokers, 2015;Harris & Dean, 2003;Harris & Drga, 2005;Lages, 2006;Rushton & Duke, 2007;Welchman, Lam, & Bülthoff, 2008;Welchman, Tuck, & Harris, 2004). These perceptual errors may contribute to behavioral failures in real world scenarios, such as catching projectiles (Peper, Bootsma, Mestre, & Bakker, 1994) and driving under foggy conditions (Pretto, Bresciani, Rainer, & Bülthoff, 2012;Shrivastava, Hayhoe, Pelz, & Mruczek, 2010;Snowden, Stimpson, & Ruddle, 1998). Here we ask if a range of systematic errors in 3D motion perception can be understood as the consequence of 3D viewing geometry and reasonable prior expectations about the world.…”