Depth, connectedness, and structural relevance in the object-superiority effect: line segments are harder to see in flatter patterns.

A briefly flashed line can be identified more accurately when it is part of certain types of pattern than in others (the 'object-superiority effects'). Three experiments were designed to investigate what aspects of these patterns determine the facilitatory effect of context. Subjects identified which of four line segments was present in various briefly flashed figures. Other subjects rated the figures for three-dimensionality, connectedness, and 'structural relevance' of the target line. Little relationship was found between connectedness ratings and accuracy in the identification task, but accuracy was highly correlated with mean depth rating (accounting for 95% of variance) and with mean structural-relevance rating (88%). Because of the high correlation (r = 0.98) between these two judgments in the present experiments, and confounding with other stimulus variables in previously published studies, the relative importance of these two global attributes cannot yet be determined definitively (though there was some evidence that for these patterns depth judgments were primary and structural-relevance judgments derivative). A reexamination of pertinent research suggests that comparisons between well-matched stimuli (as in the object-superiority effect) are likely to be more robust and informative than comparisons between lines alone and in context (the 'object-line effect').