Effects of Viewing Geometry on Combination of Disparity and Texture Gradient Information Michael S. Landy Martin S. Banks James M. Hillis
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Sources of Depth Information Motion Parallax Occlusion Stereo Disparity Shading Texture Linear Perspective Etc.
Depth Cues Motion Parallax Occlusion Stereo Disparity Shading Texture Linear Perspective Etc.
Optimal Cue Combination: Statistical Approach If the goal is to produce an estimate with minimal variance, and the cues are uncorrelated, then the optimal estimate is a weighted average where
Optimal Cue Combination: Bayesian Inference Approach From the Bayesian standpoint, the measurements D and T each result in a likelihood function These are combined with a prior distribution
Optimal Cue Combination: Bayesian Inference Approach From Bayes rule, and assuming conditional independence of the cues, the posterior distribution satisfies:
Optimal Cue Combination: Bayesian Inference Approach where p stands for the prior which acts as if it were an additional cue, and the weights are again proportional to inverse variance. Finally, assuming Gaussian likelihoods and prior, it turns out that the maximum a posteriori (MAP) estimate satisfies:
Previous Qualitative Tests that Cue Weights Depend on Reliability Young, Landy & Maloney (1993) Johnston, Cumming & Landy (1994) Rogers and Bradshaw (1995) Frisby, Buckley & Horsman (1995) Backus and Banks (1999) etc.
Previous Quantitative Tests that Cue Weights Depend on Reliability Landy & Kojima (2001) – texture cues to location Ernst & Banks (2002) – visual and haptic cues to size Gepshtein & Banks (2003) – visual and haptic cues to size Knill & Saunders (2003) – texture and disparity cues to slant
The Current Study Texture and disparity cues to slant Vary reliability by varying base slant (as in Knill & Saunders, 2003) and distance Measure single-cue reliability Compare two-cue weights to predictions Compare two-cue reliability to predictions
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Types of Stimuli Disparity-only: sparse random dots Texture: Voronoi textures viewed monocularly Two-cue stimuli: Voronoi texture stereograms, both conflict and no-conflict
Stimuli – Disparity-only
Stimuli – Voronoi textures
Cue Conflict Stimuli
Methods Task: 2IFC slant discrimination Single-cue and two-cue blocks Opposite-sign slants mixed across trials in a block to avoid slant adaptation One stimulus fixed, other varied by staircase; several interleaved staircases Analysis: fit psychometric function to estimate PSE and JND
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Single-cue JNDs: Texture
Single-cue JNDs: Disparity
Predicted Cue Weights
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Cue Conflict Paradigm
Determination of PSEs
Determination of Weights
Full Two-Cue Dataset ACHJMH
Effect of Viewing Distance
Effect of Base Slant
Outline Background: Optimal cue combination Methods: slant discrimination Single-cue results Two-cue results: perceived slant Two-cue results: JNDs Conclusions
Improvement in Reliability with Cue Combination If the optimal weights are used: then the resulting variance is lower than that achieved by either cue alone.
Improvement in JND with 2 Cues
Conclusion The data are consistent with optimal cue combination Texture weight is increased with increasing distance and increasing base slant, as predicted Two cue JNDs are generally lower than the constituent single-cue JNDs Thus, weights are determined trial-by-trial, based on the current stimulus information and, in particular, the two single-cue slant estimates
Are Cue Weights Chosen Locally?