Motion-direction specificity for adaptation-induced duration compression depends on temporal frequency.

Adapting to a 20 Hz oscillating grating reduces the apparent duration of a 10 Hz drifting grating displayed subsequently in the same location as the adaptor. The effect is orientation-independent as it remains once the adaptor is rotated 90° relative to the tests (Johnston, Arnold, & Nishida, 2006). However, it was shown that, for random dots moving at 3°/s, duration compression follows adaptation only when the adaptor and test drift in the same direction, and it disappears when they drift in opposite directions (Curran & Benton, 2012). Here, we explored the relationship between the relative motion direction of adaptor and test and the strength of duration compression for a wider range of speeds and for narrow-band stimuli (temporal frequencies between 3 and 18 Hz). We first measured perceived temporal frequency for the same stimuli after adaptation, and we used these estimates to match the apparent rate of the adapted and unadapted tests in the duration task. We found that, whereas at 3 Hz the effect of adaptation in the opposite direction on duration is marginal, at higher frequencies there is substantial duration compression in the opposite direction. These results indicate that there may be two contributions to apparent duration compression: a cortical contribution sensitive to orientation and motion direction at a wide range of temporal frequencies and a direction-independent subcortical contribution, which is revealed at higher frequencies. However, while direction specificity implies cortical involvement, subcortical orientation dependency and the influence of feedback to subcortical areas should not be ignored.