Abstract
About 30% of observers in a change-detection task with images of real-world scenes can sense the existence of a change in the display without seeing it (Rensink, 2004). Because this “mindsight” is only found in a fraction of observers, the possibility arises that it may be due to the strategic selection of a particular perceptual pathway, with the observers who experience mindsight being those who can adopt the appropriate mental set to access this system. To test this possibility, a set of experiments was carried out based on the methodology and stimuli of Rensink (2004): an original and a modified image (each of duration 240 ms) continually alternated, with a uniform gray field (duration 80 ms) between each display. Images were of real-world scenes, and changes were such that they were easily seen once noticed. Observers viewed the display and pressed a key twice: first when they sensed that a change was occurring, and then again when they saw it. Two different approaches were used to induce an appropriate mental set. The first was to precede the main experiment by a pre-task — a change-detection task which required observers to focus on either local or global structure. The second was to give observers verbal instructions beforehand to search actively or passively for change. Both approaches were compared to a baseline condition that involved no special preparations. Twenty observers were tested in each condition. Overall results were similar to those of Rensink (2004), both in terms of the proportion of observers who experienced mindsight, and the particular stimuli which created the largest effects. Although performance tended to vary slightly with pre-task and instruction set, no large differences were found. As such, these results suggest that most of the individual differences encountered in mindsight do not stem from differences in short-term mental set, but from differences in perceptual strategy involving longer-term factors.
Support provided by the Natural Sciences and Engineering Research Council of Canada.