JUDGMENTS OF RELATIVE TIME-TO-CONTACT OF MORE THAN 2 APPROACHING OBJECTS - TOWARD A METHOD

Observers reported which of as many as eight computer-generated approa ching objects would ''hit'' them first. Accuracy was above chance prob ability except when two-object displays contained pictorial relative s ize information that contradicted relative time-to-contact (TTC) infor mation. Mean d' and response time was greater, but mean efficiency (Ba rlow, 1978) was smaller with eight objects than with two. Performance was less effective when global expansion contradicted TTC information than when local expansion contradicted TTC; Results suggest that obser vers can judge relative TTC with as many as eight objects when certain sources of information are consistent with TTC and that observers rel y on information other than, or in conjunction with, optical TTC. Also , the sources of visual information that affect performance may vary w ith set size, and identification (but not detection) judgments may be constrained by limited-capacity processing.