BINOCULAR RECEPTIVE-FIELD MODELS, DISPARITY TUNING, AND CHARACTERISTIC DISPARITY

Disparity tuning of visual cells in the brain depends on the structure of their binocular receptive fields (RFs). Freeman and coworkers have found that binocular RFs of a typical simple cell can be quantitative ly described by two Gabor functions with the same gaussian envelope bu t different phase parameters in the sinusoidal modulations (Freeman an d Ohzawa 1990). This phase-parameter-based RF description has recently been questioned by Wagner and Frost (1993) based on their identificat ion of a so-called characteristic disparity (CD) in some cells' dispar ity tuning curves. They concluded that their data favor the traditiona l binocular RF model, which assumes an overall positional shift betwee n a cell's left and right RFs. Here we set to resolve this issue by st udying the dependence of cells' disparity tuning on their underlying R F structures through mathematical analyses and computer simulations. W e model the disparity tuning curves in Wagner and Frost's experiments and demonstrate that the mere existence of approximate CDs in real cel ls cannot be used to distinguish the phase-parameter-based RF descript ion from the traditional position-shift-based RF description. Specific ally, we found that model simple cells with either type of RF descript ion do not have a CD. Model complex cells with the position-shift-base d RF description have a precise CD, and those with the phase-parameter -based RF description have an approximate CD. We also suggest methods for correctly distinguishing the two types of RF descriptions. A hybri d of the two RF models may be required to fit the behavior of some rea l cells, and we show how to determine the relative contributions of th e two RF models.