Projects per year
Abstract
With luminance gratings, psychophysical thresholds for detecting a small increase in the contrast of a weak 'pedestal' grating are 2-3 times lower than for detection of a grating when the pedestal is absent. This is the 'dipper effect'--a reliable improvement whose interpretation remains controversial. Analogies between luminance and depth (disparity) processing have attracted interest in the existence of a 'disparity dipper'. Are thresholds for disparity modulation (corrugated surfaces), facilitated by the presence of a weak disparity-modulated pedestal? We used a 14-bit greyscale to render small disparities accurately, and measured 2AFC discrimination thresholds for disparity modulation (0.3 or 0.6 c/deg) of a random texture at various pedestal levels. In the first experiment, a clear dipper was found. Thresholds were about 2x lower with weak pedestals than without. But here the phase of modulation (0 or 180 deg) was varied from trial to trial. In a noisy signal-detection framework, this creates uncertainty that is reduced by the pedestal, which thus improves performance. When the uncertainty was eliminated by keeping phase constant within sessions, the dipper effect was weak or absent. Monte Carlo simulations showed that the influence of uncertainty could account well for the results of both experiments. A corollary is that the visual depth response to small disparities is probably linear, with no threshold-like nonlinearity.
Original language | English |
---|---|
Pages (from-to) | 2321-2328 |
Number of pages | 8 |
Journal | Vision Research |
Volume | 48 |
Issue number | 21 |
DOIs | |
Publication status | Published - 1 Sept 2008 |
Keywords
- Uncertainty
- Stereopsis
- Signal detection theory
- Detection
- Facilitation
- Disparity modulation
Fingerprint
Dive into the research topics of 'Discriminating depth in corrugated stereo surfaces: Facilitation by a pedestal is explained by removal of uncertainty'. Together they form a unique fingerprint.Projects
- 1 Finished
-
Mechanisms of Shading and Texture Analysis in the Perception of 3-D Surfaces
Schofield, A.
Engineering & Physical Science Research Council
1/04/03 → 30/09/06
Project: Research Councils