Abstract
Some motion information can be retained within iconic memory. Energy-based motion processing is known to be pre-attentive, whereas high-level motion processing can be described as attentively tracking the position of an object. The aim of the current study was to determine which motion information can be retained in iconic memory. Eight rotating sinewave gratings were presented simultaneously around an annulus of 5 degrees of visual angle. Each sinewave grating was presented in two 100-msec frames within which it was rotated 30 deg either clockwise or counterclockwise. The phase of the grating was either identical in the two frames or randomized, which provided local energy-based motion signals that were either strongly correlated or uncorrelated with the rotating direction thereby probing the energy-based or tracking motion system, respectively. Participants were asked to report the motion direction (i.e., clockwise vs counterclockwise) of the sinewave grating that was cued with an arrow presented at fixation. To modulate attentional resources dedicated to the target, the timing of the cue varied from 300 msec before the motion occurred (i.e., at the onset of the second frame) up to 400 msec after the motion occurred. When the phase of the sinewave grating was unchanged between the two frames, motion direction discrimination was good even when the cue was presented briefly after the motion occurred, which suggests that the energy-based rotational information was retained in iconic memory. When the phases of the two frames were uncorrelated, direction discrimination was possible only when the central cue was presented at least about 200 msec before the motion occurred and was at chance when the cue was presented briefly after the motion occurred, which suggests that high-level orientation tracking requires attention and cannot be retained in iconic memory.