My research is aimed at understanding how discrete and local signals are integrated and represented in visual cortex. I'm particularly interested in how disparity and motion are combined by the brain into "mid-level" surface representations.

For example, Preeti Verghese and I have shown that moving signals are integrated in the direction of motion. This integration cannot be explained by probability summation or by an elongated low-level detector. You can see an example of the kind of stimulus and task we used by double-clicking on the movie box at the right. The movie shows two intervals of moving dots. The first interval contains dots moving at a single speed; in the second interval, faster dots appear in a target strip elongated in the direction of motion. Observers were asked to choose the interval with the faster moving dots. We measured the speed difference necessary for observers to reliably make this discrimintion.

Note: This movie may take a minute or more to load. If you only see one interval, wait a while and double click on the image again.

The graph at the left shows speed discrimintion thresholds plotted as a function of target strip shape. Dots always translated leftward or rightward, so larger aspect ratios have target strips extended in the direction of motion. We found that thresholds decrease by about a factor of 2 as the target strip becomes extended in the direction of motion.

Another project in colloboration with Preeti and Suzanne McKee examines the precision with which disparity signals are interpolated across a surface. Observers are presented with stereograms of surfaces that contain disparity information only at the bounding contours, like the examples below. If you have a pair of red-green glasses, you can view these stereograms in depth; if not, you can still see exactly where the disparity information is by finding the parts of the images that are either red or green. The yellowish/orange parts and the black parts of the images contain no disparity information. Despite this lack of disparity information, however, observers perceive the entire surface (or object) in depth. This is surprising, because it suggests that depth is being "assigned" to a part of the image where there is no depth signal. How does this depth assignment occur? We are currently measuring the precision with which observers assign depth to the central protion of the surface.

For additional information about my work, see the publications page. For additional information about my academic background, see my vita.

Top