Journal of Vision - The intrinsic constraint approach to cue combination: An empirical and theoretical evaluation, by MacKenzie, Murray, & Wilcox

Kevin J. MacKenzie	Centre for Vision Research and Department of Psychology, York University, Toronto, ON, Canada, & School of Psychology, Bangor University, Bangor, UK
Richard F. Murray	Centre for Vision Research and Department of Psychology, York University, Toronto, ON, Canada
Laurie M. Wilcox	Centre for Vision Research and Department of Psychology, York University, Toronto, ON, Canada

We elucidate two properties of the intrinsic constraint (IC) model of depth cue combination (F. Domini, C. Caudek, & H. Tassinari, 2006). First, we show that IC combines depth cues in a weighted sum that maximizes the signal-to-noise ratio of the combined estimate. Second, we show that IC predicts that any two depth-matched pairs of stimuli are separated by equal numbers of just noticeable differences (JNDs) in depth. That is, IC posits a strong link between perceived depth and depth discrimination, much like some Fechnerian theories of sensory scaling. We test this prediction, and we find that it does not hold. We also find that depth discrimination performance approximately follows Weber's law, whereas IC assumes that depth discrimination thresholds are independent of baseline stimulus depth.