Detection of light transformations and concomitant changes in surface albedo Department of Psychology, New York University, USA Holly E. Gerhard Department of Psychology, New York University, USA,& Center for Neural Science, New York University, USA Laurence T. Maloney 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 V9 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 Vwere more than twice as great. Keywords: illumination perception, albedo perception, lightness constancy, binocular disparity, 3D perception Citation: Gerhard, H. E., & Maloney, L. T. (2010). Detection of light transformations and concomitant changes in surface albedo. Journal of Vision, 10(9):1, 1–14, http://www.journalofvision.org/content/10/9/1, doi:10.1167/10.9.1. Introduction In everyday three-dimensional scenes, the flow of light is rarely homogeneous. It depends on the location and the spectral and spatial characteristics of light sources within the scene and on the location and orientation of surfaces within the scene that absorb and reemit light, creating shadows and serving as secondary light sources. The resulting flow of light can be summarized as a light field (Gershun, 1936/1939) or, more generally, a plenoptic function (Adelson & Bergen, 1991) across the scene, a specification of the spectral power distribution of light arriving from each direction at each location in the scene. Human observers can accurately estimate light field parameters in static scenes under some circumstances (Khang, Koenderink, & Kappers, 2006; Koenderink, van Doorn, Kappers, te Pas, & Pont, 2003; Koenderink, van Doorn, & Pont, 2004; Pont & Koenderink, 2007) and reliably estimate the spatial variation of the light field across a static scene even when probed in locations that lack local cues to the light field (Koenderink, Pont, van Doorn, Kappers, & Todd, 2007). Furthermore, human observers partially discount variation in the light field 1 in judging matte surface color and lightness (Boyaci, Doerschner, & Maloney, 2004; Boyaci, Maloney, & Hersh, 2003; Gilchrist, 1977, 1980; Ikeda, Shinoda, & Mizokami, 1998; Ripamonti et al., 2004; Snyder, Doerschner, & Maloney, 2005; see Maloney, Gerhard, Boyaci, & Doerschner, 2010). In this article, we are primarily concerned with scenes consisting of achromatic matte surface patches illuminated by a single collimated neutral light source. The surfaces vary in orientation and need not be confined to a single plane. When the surfaces are confined to a single plane, we refer to the resulting configuration as a Mondrian (Land & McCann, 1971). When the surface patches differ in orientation, we refer to the resulting configuration as a crumpled Mondrian, 2 illustrated on the right side of Figures 1A and 1B. Figures 1A and 1B are two frames of a movie (Movie 1). Over the course of the movie, the direction to the collimated light source changes smoothly and periodically: it rotates smoothly around the scene, remaining at a fixed elevation above the ground plane. The angle between the light source and a surface normal to the Mondrian on the left never varies. As a consequence of Lambert’s Law (Haralick & Shapiro, 1993, pp. 2–7), there is no effect on the Mondrian’s luminances. The lighting change is invisible. The right sides of Figures 1A and 1B and Movie 1 illustrate the dramatic effect of the same changes in light source direction on a crumpled Mondrian. If the direction to the light source varied in elevation, then the effect on the Mondrian would be an overall scaling of the luminance of each surface patch in the Mondrian. The ratio of luminances of any two patches would always Journal of Vision (2010) 10(9):1, 1–14 http://www.journalofvision.org/content/10/9/1 1 doi: 10.1167/10.9.1 Received March 26, 2010; published July 16, 2010 ISSN 1534-7362 * ARVO Downloaded from jov.arvojournals.org on 06/06/2020