Human luminance thresholds were measured using a square-wave test grating (spatial frequency=0.38 cycles/deg) moving at different speeds (from 0.0° to 22°/s). A set of gratings of various spatial frequencies ranging from 0.00 (uniform field) through 23 cycles/deg provided different adapting patterns that were viewed prior to threshold determinations. The pattern of threshold elevations produced by the set of adapting gratings was different for different test-grating speeds. These results indicate that visual mechanisms with different spatial-frequency-tuning characteristics mediate the detection of a low-frequency grating when it is moved at different speeds. Also, results were obtained which suggest that the higher-harmonic components of a low-frequency grating contribute to its detection when it is moved at slow speeds.
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