Abstract
The surface properties of an object, such as texture, glossiness or colour, provide important cues to its identity. However, the actual visual stimulus received by the eye is determined by both the properties of the object and the illumination. We tested whether operational colour constancy for glossy objects (the ability to distinguish changes in spectral reflectance of the object, from changes in the spectrum of the illumination) was affected by rotational motion of either the object or the light source. The different chromatic and geometric properties of the specular and diffuse reflections provide the basis for this discrimination, and we systematically varied specularity to control the available information. Observers viewed animations of isolated objects undergoing either lighting or surface-based spectral transformations accompanied by motion. By varying the axis of rotation, and surface patterning or geometry, we manipulated: (i) motion-related information about the scene, (ii) relative motion between the surface patterning and the specular reflection of the lighting, and (iii) image disruption caused by this motion. Despite large individual differences in performance with static stimuli, motion manipulations neither improved nor degraded performance. As motion significantly disrupts frame-by-frame low-level image statistics, we infer that operational constancy depends on a high-level scene interpretation, which is maintained in all conditions.
Highlights
For our sense of vision to support our daily interaction with objects of the physical world, we must distinguish between different causes of variation in the retinal image—those that are due to the properties of objects and those that are due to the conditions of observing
How might observers disambiguate surface and lighting contributions to the image? One possible cue is that motion of the light sources or the surface will cause relative motion between patterning that belongs to the surface and spatial variation due to lighting
We test whether operational colour constancy—the ability to distinguish colour changes caused by changes in the spectral reflectance of a surface from those caused by changes in the spectral content of the illuminant [3]—is influenced by relative motion between surfaces and specular reflections
Summary
For our sense of vision to support our daily interaction with objects of the physical world, we must distinguish between different causes of variation in the retinal image—those that are due to the properties of objects and those that are due to the conditions of observing. Surface colour and surface patterning, dictated by pigmentation, can provide useful information about the identity or state of objects This information is carried in the diffuse reflectance component of light reflected from the object. For non-white objects (those with a non-uniform spectral reflectance function), diffuse and specular components differ in their spectral composition Variation owing to surface patterning is usually rigidly attached to the surface, whereas the positions of features in the specular component depend on the spatial arrangement of the surface, the light sources and the viewer. In natural viewing, these geometric relationships are rarely fixed. We summarize the perceptual signals that are available from images of glossy objects, when illuminated by lights of different spectral composition and when stationary or moving, and consider how these signals might enable human observers to identify object properties from image properties
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