Abstract
The ability to detect sudden changes in the environment is important for survival. However, studies of “change blindness” have shown that image differences are hard to detect when a time delay or a mask is imposed between the different images. However, when sensory adaptation is permitted by accurate fixation, we find that change detection is not only possible but asymmetrical: a single changed target amongst 15 unchanging distractors is much easier to detect than a target defined by its lack of change. Although adaptation may selectively reduce the apparent contrast of unchanged objects, the asymmetry in “change salience” cannot be attributed to any such reduction because genuine reductions in target contrast increase, rather than decrease, target detectability. Analogous results preclude attribution to apparent differences between (a) target onset and distractor onset and (b) their temporal frequencies (both flickered at 7.5 Hz, minimizing afterimages). Our results demonstrate a hitherto underappreciated (or unappreciated) advantage conferred by low-level sensory adaptation: it automatically elevates the salience of previously absent objects.
Highlights
Change in a scene can be a potent method for identifying an object of possible interest
Our results contradict the widely held view that the visual system is poor at detecting change amongst multiple items in the absence of transients
It is generally agreed that even no-change detection is possible when transients are allowed
Summary
Change in a scene can be a potent method for identifying an object of possible interest. In four separate experiments we investigated the effects of test duration, target contrast, target delay, and target temporal frequency on detection of the odd-man-out The purpose of these investigations was to determine which, if any, of these stimulus attributes were critical for detecting change. It is known that adaptation to a moving stimulus reduces the perceived speed of subsequent tests (Thompson, 1981), and further evidence suggests that slowly moving stimuli are harder to find amongst faster distractors than vice versa (Ivry & Cohen, 1992; Rosenholtz, 1999) These results are not directly relevant to our stimuli, which were flickering rather than moving, but it is possible that the previous results for speed are mediated by changes in perceived temporal frequency. The results (Fig. 2, bottom right) showed that reducing the temporal frequency of the target facilitated its detection in the target-same conditions, but had little effect in the target-change conditions, suggesting that detection in the latter case was not based on apparent temporal frequency
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