The original studies of mental rotation estimated rates of imagining rotations that were much slower when two simultaneously portrayed three-dimensional shapes were to be compared (R. Shepard & J. Metzler) than when one two-dimensional shape was to be compared with a previously learned two-dimensional shape (Cooper and her associates). In a 2 X 2 design, we orthogonally varied dimensionality of objects and type of task. Both factors affected reaction times. Type of task was the primary determiner of estimated rate of mental rotation, which was about three times higher for the single-stimulus task. Dimensionality primarily affected an additive component of all reaction times, suggesting that more initial encoding is required for three-dimensional shapes. In the absence of a satisfactory way of controlling stimulus complexity, the results are at least consistent with the proposal that once three-dimensional objects have been encoded, their rotation can be imagined as rapidly as the rotation of two-dimensional shapes.
Two experiments showed that continuity of the pitch contour is an important perceptual indicator that a formant pattern comes from a single speech source. Subjects listened to repeatedly played formant patterns that changed smoothly between two vowels. When the pitch was a monotone, these patterns were heard as containing semivowels and liquid consonants; but when a discontinuous, steplike pitch contour was imposed on the patterns, they divided into two perceptually distinct speech sources, and the phonemic percept changed to a predominance of stop consonants. In the second experiment, this effect was shown to be due to changes in pitch itself, rather than to concomitant changes in amplitude or energy. Earlier suggestions that continuity of both formant structure and pitch contour are important for the perceptual coherence of speech were borne out.
Two experiments were carried out on how questions are remembered. Subjects watched a videotape of a series of simple events and then answered 18 questions about these events. The questions were all of the same general syntactic form (e.g., "Did the pencil fall against the jug on A?", where A refers to a particular location). They were designed to elicit three sorts of answer: "yes," "no" because the event took place at another location, and "no" because the event did not take place at all. After the subjects had answered the questions, they were given an unexpected test of their ability to recall them. A difference in the memorability of the questions was predicted on the basis of a procedural theory of comprehension and a hypothesis about memory; subjects should cease to process a question when they realize that it concerns an event that did not take place, and such questions should be harder to remember because they are processed to a lesser degree than the other sorts of question. Experiment 1 confirmed the predictions, but its results in part could be accounted for by assuming that subjects recalled the original events and used them as a cue to remembering the questions. Experiment 2 eliminated this explanation by showing that when subjects do not have to answer certain questions, their recall of them is very poor. However, the same differences in the memorability of the three sorts of question were obtained for both answered and unanswered questions.
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