Directional scanning of remembered visual patterns.

We report a set of experiments that helps to define the conditions under which mental image scanning may be used spontaneously for specific, practical purposes. Subjects were shown a dot pattern, followed by an arrow, and their task was to say whether the arrow was pointing at any of the previously seen dots. When no advance information was provided about the arrow's location, reaction time for correctly verifying that an arrow was pointing at a dot increased linearly with increasing arrow-dot distance, and the subjects almost always reported scanning a mental image in order to make their judgments. However, when a cue for the arrow's location was presented 2 sec beforehand, reaction time was uncorrelated with distance, and most of the subjects reported using an alternative strategy based on the determination in advance of correct directions from that location to the dots. When given only 1 sec of advance information about arrow location, most subjects reported using a combined image-scanning and advanced determination strategy, resulting in a reaction time function that increased only for the farthest distances. Because in each of these experiments instructions to form or to scan mental images were never given, these findings address the most common criticisms of the image-scanning paradigm.