Stereoscopic depth discrimination with contrast windowed stimuli.

Depth discrimination with a shifted contrast window was compared to that with a fixed contrast window. Stereoscopic performance with the fixed window was limited to small disparities and varied with spatial frequency. Performance with the shifted window extended to larger disparities and was more similar for low and high spatial frequencies. The results depended upon window shape, indicating that edge blur is an important factor. Stereoscopic performance with shifted patterns was supported at disparities larger than a phase disparity model might predict, suggesting that a combination of position and phase disparity computations are used for the perception of stereoscopic depth.

Inducing blindsight in normal observers.

We attempted to induce blindsight in normal observers, in an effort to replicate and extend the findings of Kolb and Braun (1995). In that demonstration, observers were able to localize a target in the absence of visual awareness, indicated by the lack of a correlation between localization accuracy and confidence ratings. Replication of this work seemed essential, given the failed attempt by Morgan, Mason, and Solomon (1997). A key aspect of the present work was the use of a pointing response, which is believed to have access to the unconscious representations subserving blindsight. In the critical rivalrous condition, the display consisted of Gabor patterns presented dichoptically with orthogonal orientation in each eye. Binocular summation of left and right images combined to give the appearance of a uniform plaid, camouflaging the texture-defined target. Our attempt to demonstrate blindsight in normal observers was unsuccessful, in that the localization accuracy of the texture-defined target and the observers' confidence ratings were positively correlated. Although the replication was unsuccessful, the results are valuable in that they provide closure to this widely publicized but fruitless line of inquiry.