False Memory
Individuals vary in their ability to report details of previously experienced sensations and spatial relationships. Differences in mental imagery span a wide range with some being able to report vivid picturelike images in their mind while others report images that are blurry or distant. Cognitive psychologists debate whether the differences reflect differences in being able to imagine reality or whether they merely reflect differences in reporting style.
Sheppard and Metzler’s Paradigm
This lab activity is inspired by a paradigm developed by Sheppard and Metzler (1971) who pioneered the study of mental rotation as a way to objectively probe mental imagery ability. You will complete 10 practice trials and 60 experimental trials. Each trial begins with fixation followed by presentation of two images each containing a three-dimensional object composed of cubes. Your task is to press the “D” key if you think they are the same object and press the “K” key if you think they are different. You will receive feedback about whether your response is correct or incorrect. You will notice that some trials are harder than others because in order to determine if the objects are the same, you will have to rotate the object by a varying number of degrees in your mind to determine whether it can be the target object.
Mental Rotation and Decision Speed
Sheppard and Metzler’s results showed that for every 30 degrees of rotation, an individual requires about 600 additional milliseconds to make a decision in the mental rotation task. Some trials are very easy because the two objects are identical (i.e., there was no rotation). Other trials are very difficult because the two objects are different so that no amount of rotation can be done to rotate one object to match the other. “Different” trials tend to have decision times longer than all “same” trials because the participant has to rotate the object many different ways and through all degrees to be sure that the image is not the same object. Participants tend to show a flat decision time function for “different” trials, and an increasing function for “same” trials where rotation increases from 30 degrees, 60 degrees, 90 degrees, and 120 degrees.
Rotation and Mental Imagery
Sheppard and Metzler’s findings support the idea that mental imagery manipulations are similar to manipulations in the physical world. In both the real world and in your mind, it takes longer to manipulate a test object to match a target object the more the test object has been rotated.