Abstract
Verstraten et al. (2000) examined the temporal limit for attentive tracking of an object within a circular ambiguous apparent motion display consisting of several luminance-defined discs. They found that the limit was 4–8 Hz, much lower values than for first-order motion detection. They argued that this demonstrates a higher-level involvement. To clarify the nature of this higher-level involvement, we examined the temporal limits for attentive tracking by using stimuli defined by several different attributes (luminance, binocular disparity, motion direction, and flicker). The experiment was conducted in either within-attribute (motion between arrays defined by the same attribute) or cross-attribute (motion between arrays defined by luminance and those defined by the other attribute) conditions. Two circular arrays of four rectangle objects (1 × 1 deg) were alternately presented with no ISI. The diameter of the arrays was 7 deg. The alternation rate was varied in 5 steps between 1.67 and 5.00 Hz. Participants were asked to track one object (target) for 1.8 sec. The maximum temporal rate was defined as the rate that corresponds to 75% correct responses. It was found that the upper temporal limit was approximately 4 Hz in within-attribute conditions regardless of attributes. The cross-attribute conditions yielded much lower limits. It was about 2–3 Hz irrespective of attributes paired to luminance. These results indicate that, (1) the 4–8 Hz limit is specific to tracking with objects defined by single attribute, (2) this limit is not affected by attribute types including first- and second-order difference, and (3) cross-attribute trackings involve a much slower higher process than that for within-attribute trackings. There seems two separate types of object trackings; one for within-attribute, and the other for cross-attribute trackings.