Intentional (attentional) control of Bi-stable apparent motion depends upon retinal location

Purpose. Reseach has shown that numerous factors (e.g. distance, size, contrast, color, orientation, surface interpretation) can influence perceived solution to the correspondence problem in a bi-stabie (competitive) apparent motion display. In many cases, however, "intentional (attentional) effort" can override these image factors. The present study is an attempt to understand how conscious effort controls perceived apparent motion. Methods. A horizontal pair of circles (5.76° apart), one large (1.53°) and the other small (0.76°), was presented symmetrically across the vertical meridian either at the fixation level or 6° above or below the fixation cross. The locations of the two circles were switched from frame to frame. The perceived apparent motion was either 1) the two circles expanding and contracting in place, or 2) the two circles moving across to exchange positions. The observer saw eight frames (no ISI) per trial and indicated which motion was seen. The vertical eccentricity (0° or 6°) and the frame duration (150 - 600 msec) were varied randomly from trial to trial. The observer ran in three intentional (attentional) conditions: 1) passive viewing, 2) attempting to see the expansive motion, and 3) attempting to see the translational motion. The three conditions were blocked. The observer always fixated the fixation cross. Results. In general, more translational motion was seen with longer frame duration. For passive viewing, the expansive motion was seen slightly more at 0° vertical eccentricity whereas the translational motion was seen slightly more at 6° (-10% effects). At 0°, the effort dramatically increased the probability of the expansive motion relative to passive viewing, but had no effect on the translational motion regardless of frame duration. At 6°, however, the effort increased the translational motion, but facilitated the expansive motion only for the longest frame duration (600 msec). Conclusions. Substantial interactions obtained between the type of conscious effort and spatial-temporal parameters indicate that the effects of intention (attention) could not be explained by simple criterion shifts. In the present experimental paradigm, the intentional (attentional) control of apparent motion accentuated the intrinsic anisotropy of the visual field. Conversely, the results suggest that attempts to measure the anisotropy of the visual field may be undermined under passive viewing conditions.