Dimension- and space-based intertrial effects in visual pop-out search: modulation by task demands for focal-attentional processing

The distance effects appear to be dependent mainly on the spatial separation of the current from the preceding target, where larger distances necessarily involve crossing of the vertical and horizontal field meridians. Further analyses of the distance effects in terms whether they occurred within the same field quadrant, crossed the vertical meridian only, the horizontal meridian only, or both meridians revealed meridian crossing costs (which were unaffected by the number of meridians crossed), consistent with prior studies of the reallocation of attention to an (invalid) target following the presentation of a spatial cue at a nontarget location (e.g., Rizzolatti, Riggio, Dascola & Umiltà, 1987; Egly & Homa, 1991). However, it is not clear whether this pattern in the present data reflects a true meridian crossing cost, distinct from a pure distance effect. In an attempt to distinguish between the two types of effect, the data for distance d3 (i.e., the maximum distance possible within a quadrant; for shorter distances, the data available for analysis were insufficient) were examined for meridian crossing effects. This analysis failed to reveal RTs to new targets presented across one or both field meridians relative to the old target to be longer than RTs to targets presented within the same quadrant. While this suggests a pure distance effect, it cannot be really ruled out that meridian crossing plays a role as well, as even with d3 there were too few data available to reliably estimate performance in the respective conditions.

This pattern of effects is very similar to that found by Hommel (1998) in a prime-probe task, that is, dimension, position, and response repetition effects are large when other aspects also repeat; but they are reduced, absent, or even reversed when another aspect changes. As this pattern is evident across perceptual (dimension and position) and response-related aspects of processing, it is possible that these effects also involve some central processing stage (besides perceptual and response-related stages per se)—such as a stage of ‘feature-response binding’ assumed in Hommel’s (1998) ‘event file’ theory.