Two competing sensations of apparent movement were produced by the rapid alternation of two multielement stimulus frames. Either sensation could be made dominant by, appropriate manipulations of the stimulus display. The results suggest that there are two systems capable of generating movement signals in man. One system depends on preliminary processing of form, and the second system does not.

No abstract

The total-time hypothesis states that a fixed amount of time is necessary to learn a fixed amount of material regardless of the number of individual trials into which that time is divided. The evidence indicates that the hypothesis can be expected to hold whenever task requirements do not exceed simple rehearsal, and whenever effective time, the time during which rehearsal is actually evoked, bears a positive linear relationship to nominal time. The total-time relationship, with a distinction between nominal and effective time, provides plausible explanations of both the results of prompting and confirmation studies and the von Restorff effect.The total-time hypothesis states that a fixed amount of time is necessary to learn a fixed amount of material regardless of the number of individual trials into which that time is divided. If, for example, it takes 10 seconds to learn each of the items of a given list, the total-time hypothesis would predict that a subject could reach criterion in either 20 .5-second-per-item trials or 10 1-secondper-item trials or 5 2-second-per-item trials or 1 10-second-per-item trial.Two procedures have generally been used to test the total-time hypothesis. In one, although different groups of subjects are presented the to-be-learned material at different rates, total learning time is held constant, and number of items correct is compared for the various conditions. For example, the performance on the first trial of a group learning at a 4-second rate is compared with the performance on the second trial of a group learning at a 2-second rate. In the other, although different groups of subjects are presented the to-be-learned material at different rates, learning is carried to the same criterion, and total time to reach this criterion is computed. With both these procedures, support for the total-time hypothesis rests on 1 The authors are indebted to Benton J. Underwood for stimulating their original interest in the total-time hypothesis and for providing helpful suggestions during the writing of this article.

Inspecting a pattern of alternating dark and light bars makes it difficult to see a similar pattern presented afterward. This phenomenon can be used to isolate mechanisms responsive to bars of a given width. Our results suggest that the human visual system contains several different classes of size detectors, each maximally sensitive to visual targets with sizes in a particular range.

The perceived motion of a vertical sine-wave luminance grating which undergoes an abrupt 180 deg phase shift (motion step) is ambiguous. The grating sometimes appears to move rightward; sometimes leftward. However, when the 180 deg step follows closely upon an unambiguous grating step, the 180 deg step appears to be in the same direction as the unambiguous step. This phenomenon is termed visual motion priming (VMP), and some of the characteristics of the phenomenon were investigated in a series of experiments. The main findings were that priming (1) lasted for hundreds of msec; (2) was at a maximum when the magnitude of the priming step was 90 deg; (3) was scarcely affected by spatial frequency in the range 0.7-2.8 c/deg; and (4) at suprathreshold contrasts depended upon the relative contrast, not the absolute contrasts, of the frames comprising the priming step. The experiments were conducted within the framework of a motion energy model (Adelson & Bergen, 1985) which possessed an extra stage which summed motion signals over time. Some of the results could be explained by the second-stage integrator. Other nonlinear relationships between VMP and contrast require some form of motion signal compression, and perhaps even a mechanism of dynamic contrast processing.