Viewing a spatially-blurred or sharpened edge causes a focused edge to appear too sharp or blurred, respectively. We asked whether similar adjustments influence the perception of temporal edges, by measuring the appearance of step changes in luminance after adapting to gradual or abrupt temporal transitions. Stimuli were spatially uniform 6 deg fields presented on a monitor at a 160 Hz frame rate. The field luminance was varied in a squarewave (1 to 4 Hz) that was blurred or sharpened by filtering the slope of the amplitude spectrum. All stimuli were scaled after filtering to have the same mean luminance (40 cd/m2) and rms contrast (0.35). In a nulling task, a 2AFC staircase was used to set the filtered slope of successive 1-sec test stimuli until they appeared as a step change, with measures made before or after 2-min adaptation to blurred or sharpened flicker. In an additional matching task, the staircase instead varied the temporal spectrum of flicker in a matching field until it appeared to match a step change presented in a test field, following adaptation to different levels of blurring in the adapt and match fields. Subjects showed good accuracy in setting the flicker to a squarewave (with slope 1/f). However, after viewing blurred flicker, this squarewave appeared too sharp and thus the settings shifted to steeper slopes, while sharpened flicker induced the opposite aftereffect (though these shifts appeared less salient and less consistent than comparable aftereffects in the spatial domain, perhaps reflecting the weaker visual selectivity reported for temporal frequency than spatial frequency). Analogous effects were also found in an induction task - squarewave flicker appeared sharpened (blurred) when surrounded by blurred (sharpened) flicker. These results suggest that visual adaptation and induction may play an important role in calibrating perceived focus not only in space but also in time.

Supported by EY-10834