Simultaneous density contrast is bidirectional.
Simultaneous density contrast, or SDC, is the phenomenon in which the perceived density of a textured region is altered by a surround of different density (Mackay, 1973). SDC provides an experimental tool to investigate mechanisms of density coding, yet has not been systematically examined. We measured SDC with a 2AFC staircase procedure in which human observers judged which of two patterns, one with and one without a surround, appeared more dense. We used a range of surround densities varying from very sparse to very dense (0-76.8 dots/deg2), and two center test densities (6.4 and 12.8 dots/deg2). Psychometric functions were used to estimate both the points of subjective equality (PSE) and their precision. Unexpectedly we find a bidirectional SDC effect across the five observers: Not only does a denser surround reduce perceived density of the center, but a sparser surround enhances its perceived density. We also show that SDC is not mediated by either contrast-contrast or spatial-frequency contrast. Our results suggest the presence of multiple channels selective for texture density, with lateral inhibitory interactions between them.
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada; hua-chun.sun@mail.mcgill.ca; https://www.researchgate.net/profile/.
Hua-Chun
HC
Sun
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada; curtis.baker@mcgill.ca; http://mvr.mcgill.ca/Curtis/cbaker_home.html.
Curtis L
CL
Baker
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada; frederick.kingdom@mcgill.ca; http://mvr.mcgill.ca/Fred/fkingdom_home.html.
Frederick A A
FA
Kingdom
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D016002:Discriminant Analysis; D005364:Field Dependence-Independence; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011594:Psychometrics