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gabor_grid

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Summary

This binocular stimulus consists of a grid of drifting Gabor patches. It is designed to emulate the pseudoplaid stimulus of Rokers, Czuba, Cormack and Huk (2011, Journal of Vision).

Gabor functions at two orientations are displayed in both eyes. When they are matched across eyes, the orientations are the same but the directions of drift are opposite. If motion is integrated across patches, then the stimulus in each eye can be seen as moving in the pattern direction. Opposite left-right pattern directions in both eyes can lead to the perception of motion in depth.

Examples

• gabor_grid_full.stm - 2016 Jun 5 - Movie (.mov) - Full 5 by 5 grid of Gabor patches.
• gabor_grid_sparse.stm - 2016 Jun 5 - Movie (.mov) - Sparse 8 by 8 grid of Gabor patches.

Imperfections

The current stimulus generation algorithm runs slower than necessary because each Gabor is drawn within an image having the full size of the stimulus field. A faster algorithm could easily be developed.

Some features of the Rokers et al. (2011) stimulus have not been implemented, such as the limited lifetimes of the Gabor patches and the ability to prevent binocular matches across the eyes.

Parameters

• grid_type - 'simple' - this type of grid consists of Gabor patches that are matched in location and orienation across the eyes. The grid locations may be fully or sparsely populated by Gabor patches. Each Gabor patch is randomly chosen to have a direction of drift (and corresponding orthogonal orientation) specified by theta1 and theta2 (relative to direction). The initial phases of the grating patches are randomly chosen.

• sf - (cyc/deg) spatial frequency of the sinewave component of the Gabor function.

• tf - (Hz) temporal frequency of the drifting sinewave component of the Gabor function.

• contrast - (0..1) contrast of the sinewave component of the Gabor function.

• direction - reference direction from which theta1 and theta2 are measured.

• theta1 - (deg) direction of motion, relative to direction, of the first type of Gabor patch.

• theta2 - (deg) direction of motion, relative to direction, of the second type of Gabor patch.

• sd_par - (deg) standard deviation of the Gaussian Gabor envelope running parallel to the orientation of the sinewave.

• sd_orth - (deg) standard deviation of the Gaussian Gabor envelope running orthogonal to the orientation of the sinewave.

• grid_w - number of horizontal positions in the underlying grid on which the Gabor patches are centered.

• grid_h - number of vertical positions in the underlying grid on which the Gabor patches are centered.

• box_w - (deg) horizontal distance between neighboring grid locations.

• box_h - (deg) vertical distance between neighboring grid locations.

• n_patch - number of Gabor patches to place (randomly) on possible grid locations. Must be less than or equal to grid_w times grid_h. If set to -1, then the grid will be full (n_patch = grid_w * grid_h).

• dir_balance - This controls the number of Gabor patches that will be chosen to have direction theta1 in the left eye. Thus, if n_patch is even and this parameter is set to 0.5, then exactly half of the patches will have the orientation associated with theta1, and the other half will have the orientation associated with theta2.

• seed - randomization seed that determines the choice of direction, starting phase, and locations (if the grid is sparse) of the Gabor patches.

General stimulus control

• stim_monocular ['both'] or 'left' or 'right'. This is a general stimulus parameter that defaults to the value, both, but can be set to either left or right to blank out the other eye's image, which is set to the background value. For example, when set to left, the left eye image is displayed normally while the right eye image is replaced with the background value, typically mean gray.

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