Glass-pattern detection is tuned for stereo-depth

We investigated the role of disparity information in the detection of global form. Glass patterns, which allow insight into processing at both local and global stages of form analysis, were used as stimuli. We determined how detection of concentric Glass patterns is affected by a disparity difference introduced between partner dots forming local dipoles (Experiment 1), and how detection is affected by the addition of randomly oriented dot-pairs (noise dots) at crossed and uncrossed disparities (Experiment 2). The first experiment showed that detection thresholds increased when partner dots were separated in depth at disparities greater than approximately 17 min arc; the second experiment showed that noise dots disrupted the detection of form if they were presented at disparities of between approximately +/-20 min arc from the Glass pattern's presentation depth plane. Our findings suggest that disparity information plays a role in the recovery of the image structure and, importantly, local and global form mechanisms were found to be selective for a small range of stereo-depths. We discuss the findings of our study in the light of current evidence indicating that a common neural substrate is responsible for the analysis of form and binocular disparity.