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bar field

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Summary

This field of coherently moving bars decouples the direction of motion from the orientation of the bars. This type of stimulus was used by Lorenceau, Shiffrar, Wells and Castet (1993) in psychophysical experiments and by Pack and Born (2001) to study area MT cells.

Examples

• bf_3x4.stm - 2017 Sept 27 - Movie (.mov) - A bar field oriented 30 deg away from the direction of motion.

Imperfections

The c-code is inefficient - it calls a single bar-drawing routine many times, which examines the entire xn by yn stimulus field. This could easily be sped up many-fold.

Parameters

• st0 - Start time (s)

• stn - Duration (s) of the bar field. If center_motion is set to 1, then the bar field will be centered on (cx,cy) at time stn/2.

• cx - Center of bar field in horizontal axis (deg)

• cy - Center of bar field in vertical axis (deg)

• direction - Direction of movement (deg)

• length - Bar length (deg)

• width - Bar width (deg)

• speed - Movement speed (deg/s)

• ampl - Bar luminance [0..1]

• bar_ori - Bar orientation (deg, 0=vertical). Defaults to direction if this parameter is not present.

• center_motion - Automatically center the motion path in time within stn duration

• field_wid_n - Number of bars along width of field

• field_len_n - Number of bars along length of field

• field_wid_off - Offset of bars along width of field (deg)

• field_len_off - Offset of bars along length of field (deg)

• bgval - Background luminance (0..1)

• maxlum - Maximum luminance, default is 1

• sdaa - spatial scale for anti-aliasing (pixels)

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