Human visual system's selective sensitivity to a rate of change of spatial frequency

Anstis and Rogers (Anstis, 1997) failed to find evidence for a visual mechanism that independently responds to gradual change of spatial frequency. However, their results could have been confounded with motion aftereffect due to their adaptation grating which continued to expand in only one direction. This study addresses this possible confound by including adaptation gratings designed to prevent the motion aftereffect. This is achieved by alternating the adaptation grating's center of expansion between the left and right edges of the stimulus field in order to cancel out the effect of the direction of an expanding motion. This study hypothesizes the existence of channels sensitive to changing spatial frequency: thus, the adaptation to a changing-frequency stimulus would produce the changing-frequency aftereffect that is different from the classical motion aftereffect and selective to a rate of change of spatial frequency.

The results were as follows. (a) The observer's adaptation to an expanding grating selectively influenced the observer's sensitivity to an expanding test grating. Adaptation to a contracting grating selectively influenced the sensitivity to a contracting test grating. (b) The observer's sensitivity was most depressed in the test spatial frequencies falling within the range of adaptation spatial frequency. (c) The aftereffect was much reduced or not even produced when the adaptation stimulus exceeded 1–1.5 deg in width.

These results suggest that the previous study by Anstis and Rogers (Anstis, 1997) may have been confounded, and then contribute to the evidence for a human visual pathway which contains channels that are selectively sensitive to a unidirectional rate of change of spatial frequency.