>Psychtoolbox>PsychDemos>PsychExampleExperiments

MinimumMotionExp([writeResult=0])

Minimum motion luminance measurement (Anstis and Cavanagh). Rapid,
precise, and works well down to 1hz, or 1 cpd. Self-contained script,
with optional gamma file input or default.

Measures red/green and blue/green foveal or extrafoveal equiluminance
using the Cavanagh, MacLeod and Anstis (1987) sinusoidal minimum motion
stimulus, here drawn as a windmill.

One component of the test stimulus is a rotary sine wave where peaks of 1
phosphor coincide with troughs of a second phosphor. This is counterphase
modulated in cosine phase is space and time. A “luminance lure” grating
is added in spatial and temporal quadrature (sine phase). The stimulus
appears in clockwise or anticlockwise motion, depending on the relative
luminance of two phosphors. The ratio of the two phosphor intensities is
adjusted using the mouse. The isoluminant point is the precise point
where the motion direction changes, and there the motion is replaced by
counterphase flicker. User selects whether to measure the red phosphor
luminance relative to the green, the blue phosphor luminance relative to
the green, or the blue phosphor luminance relative to the red. Reported
values are the ratios of phosphor luminances when each phosphor is at
maximum intensity. Average stimulus chromaticity and luminance are kept
constant during the adjustment.

The stimulus is produced by clut animation (palette mode). If BPP is
nonzero, we assume that DVI video output is relayed to the monitor via a
CRS BitsPlusPlus device, or via a DataPixx/ViewPixx device allowing fine
control of modulation depths and corresponding precision in luminance
estimates. Otherwise set BPP to zero. In either case, Psychophysics
Toolbox 3 and Matlab 7.4 or later (or Octave 3.2 or later) are required.

Note: Writing of result files is disabled, but can be enabled in a
“production setting” by providing the optional argument ‘writeResult’ as

This script is contributed by Don MacLeod, UCSD. It was modified by Mario
Kleiner for portability across all supported operating systems and for
optimized speed.