Contrast sensitivity and adaptation as a function of grating length.

For gratings of variable length (L), contrast sensitivity increased with square root L up to a critical value equal to the width of 7-14 grating cycles, for spatial frequencies throughout the range 4-32 c/deg. For multiple gratings the critical value was the same, but the increase in sensitivity with length was more gradual. Adaptation to both single and multiple gratings produced length-specific elevation of thresholds with a bandwidth greater than 2 X that of spatial frequency-specific adaptation. The findings are interpreted in terms of multiple, independent channels tuned to spatial frequency and orientation, with the encoding of length dependent on simultaneous activity in several such channels.