gabor_britt

Summary

This dynamic, random stimulus consists of two moving Gabor patches that are presented simultaneously at randomized positions on an underlying square spatial grid. It is designed to emulate the stimulus of Britten and Heuer (1999, J Neurosci) that was used to probe the linearity of spatial summation within the receptive fields of neurons in area MT.
In this stimulus, the entire Gabor patch moves, rather than having the phase of the sinusoid shift beneath the Gaussian window.
The stimulus can be run in single-patch mode to measure single-patch responses for computing the linear predictions for comparison to dual-patch responses.

Examples

gabor_britt_demo.stm - 2017 May 3 - Movie (.mov) - Two translating patches on a 5 by 5 grid.

Imperfections

None reported.

Parameters

grid_xn - number of horizontal (and vertical) positions in the underlying grid on which the Gabor patch motion is centered.

grid_dx - (deg) horizontal (and vertical) distance between neighboring grid locations.

n_patch - number of Gabor patches to place randomly on the possible grid locations. Values of 1 and 2 are currently allowed.

direction - (0..360) sets the direction of motion of the translation of the patch and the orientation (orthogonal to the motion) of the underlying sinusoidal grating.

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

etf - (Hz) effective temporal frequency of the translating Gabor patch.

phase - (0..360) the fixed spatial phase of the Gabor patches.

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.

g_amp - an amplitude value to be used to adjust the Gabor function template to have amplitude 1.0 at its max (or -1.0 at its min) so that contrast can then be used to adjust the contrast within the usual range of 0..1.

contrast - (0..1) contrast of the Gabor function.

dur_full - (sec) duration of the full contrast portion of the sweep of one epoch of movement.

dur_ramp - (sec) duration of the contrast ramp before and after the full contrast portion of the sweep. This will be used to pick an integer number of frames during which the contrast is neither zero nor full contrast. Setting this to 0 means there will be no ramping up or down of contrast.

dur_sep - (sec) additional zero-contrast frames between each stimulus epoch. There are always a minimum of two blank frames between stimuli.

ranseq_offset - For each trial, the full number of possible spatial configurations are computed and randomly sequenced based on the seed value. This value determines which index in that random sequence will be used to position the stimuli in the first epoch within the trial. Positions are then picked in sequence starting from that first value, and they wrap around if necessary, meaning if the trial is long enough and enough epochs have been requested.

n_epoch - The number of stimulus epochs to show within one trial. If this is set to 0, then the maximum number of epochs will be computed and used.

seed - randomization seed that determines the sequence of locations of the patches.

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