Publication Type:Journal Article
Source:Spatial vision, Volume 7, Number 4, p.311–22 (1993)
Keywords:Attention, Attention: physiology, Form Perception, Form Perception: physiology, Humans, Light, Ocular, Ocular: physiology, Psychophysics, Sensory Thresholds, Vision
Shading was used to generate the appearance of an obliquely illuminated surface with spherical indentations and protrusions. The "pop-out" of an apparent indentation among numerous apparent protrusions served as a psychophysical assay for shape-from-shading. Detectability of the pop-out varied with the direction of apparent illumination, a finding which is characteristic for shape-from-shading and which demonstrated the appropriateness of this assay. Observers were able to concurrently detect two shape-from-shading pop-outs in different parts of the display, demonstrating that shape-from-shading is a parallel process. In another experiment, visual attention was engaged by a letter discrimination task. Nevertheless, observers were able to detect a shape-from-shading pop-out concurrently in the unattended part of the display, suggesting that shape-from-shading is independent of visual attention. Thus, shape-from-shading shares some of the characteristics of Julesz' textural stimulus dimensions ('textons').