Detection of light transformations and concomitant changes in surface albedo

Abstract

We report two experiments demonstrating that (1) observers are sensitive to information about changes in the light field not captured by local scene statistics and that (2) they can use this information to enhance detection of changes in surface albedo. Observers viewed scenes consisting of matte surfaces at many orientations illuminated by a collimated light source. All surfaces were achromatic, all lights neutral. In the first experiment, observers attempted to discriminate small changes in direction of the collimated light source (light transformations) from matched changes in the albedos of all surfaces (non-light transformations). Light changes and non-light changes shared the same local scene statistics and edge ratios, but the latter were not consistent with any change in direction to the collimated source. We found that observers could discriminate light changes as small as 5 degrees with sensitivity d' > 1 and accurately judge the direction of change. In a second experiment, we measured observers' ability to detect a change in the surface albedo of an isolated surface patch during either a light change or a surface change. Observers were more accurate in detecting isolated albedo changes during light changes. Measures of sensitivity d' were more than twice as great.

Intuitive understanding of the relation between velocities and masses in simulated collisions

“…1 We varied the implied masses of the colliding objects by manipulating their simulated materials (Experiment 1) and their sizes (Experiments 2 and 3). Research on the visual perception of material appearance (for reviews, see Anderson, 2011;Maloney & Brainard, 2010) has shown that the surface properties of objects, such as texture, reflectance, colour, and so on, provide unique information about the materials of which objects are made. The phenomenon of "material-weight illusion" lends support to the hypothesis that visually perceived material influences both the expected and the haptically perceived masses of objects (Buckingham, Ranger, & Goodale, 2011;Ellis & Lederman, 1999).…”

Estimating changes in lighting direction in binocularly viewed three-dimensional scenes

“…We have shown in previous psychophysical experiments that human observers utilize binocular disparity to correct the shading gradient direction when estimating the illuminant direction (Gerhard & Maloney, 2010). Thus, we included the shape map in our model, which was used to correct the local gradients in concave regions.…”

“…Estimating illuminant direction from first-order directional derivatives of the luminance map is not a novel idea (Knill, 1990;Lee & Rosenfeld, 1985;Pentland, 1982) but correcting the derivatives for the measured local 3D shape information is. Because we have shown in previous psychophysical experiments (Gerhard & Maloney, 2010) and in the experiment reported here that human observers correct for concave regions when judging lighting direction in stereoscopic scenes, we included a concavity correction in the model.…”

“…They found that observers could effectively interpolate the light field at locations within the scene distant from any reference object. Gerhard and Maloney (2010) examined human ability to discriminate transformations of the pattern of scene luminance induced by altering the direction of a collimated 1 light source from non-light transformations that shared the same local scene statistics. They found that observers were accurate in discriminating light and nonlight transformations and that they were more sensitive to a concomitant change in the albedo of a surface patch under a light transformation than under a non-light transformation.…”

“…Observers utilized the stereo information to estimate rapid, small changes in light source direction and performed near ceiling in estimating the direction of change (Gerhard & Maloney, 2010).…”