An aftereffect to discrete stimuli producing apparent movement and succession

After observing the sequential flashing of two lights that produced either the perception of apparent movement or the perception of the succession of two stationary lights, the presentation of the lights in the opposite direction produced the perception of a more rapid apparent movement or of a more rapid succession of the light flashes. These aftereffects suggest the presence of neural structures for the discrimination of sequential changes in spatial position which are subject to adaptation and respond with decreased sensitivity to the repetitive presentation of the two lights in a given spatial direction. The results are interpreted to support the hypothesis that the perception of apparent movement involves the excitation of specific neural mechanisms selectively responsive to sequential changes in stimulus position. An alternative hypothesis is that the perception of apparent movement involves an inference based on the separate registrations of the position of a stimulus at one point in time and the position of that stimulus at an earlier point in time.     

Spatial-contrast movement aftereffect can be rotary: support for link with aftereffect of induced movement.

The procedure for eliciting movement aftereffect (MAE) involves the subject's adapting to visual movement that subsequently stops. Conventionally, MAE is confined to the area of movement adaptation. However, Wohlgemuth (1911) demonstrated the existence of a type of MAE that had the opposite characteristics of an adjoining conventional MAE; the test area was unpatterned during adaptation and patterned during testing. This spatial-contrast MAE may be connected with the more recently identified induced movement MAE. Unfortunately, the eliciting movements have not necessarily been comparable; Wohlgemuth used centrifugal and centripetal movement, whereas induced movement MAE has generally been rotary. The results of this study indicate that rotary spatial-contrast MAE can be elicited by a display that, with modification, also elicits induced movement MAE and that the rotary spatial-contrast MAE is weaker than the equivalent induced movement MAE.     

Global cooperativity of the short-range process in apparent movement: evidence obtained with contour-containing stimuli

Previous research has demonstrated that the short-range process in apparent movement, as studied with random-dot cinematograms, exhibits global cooperativity; that is, computations performed by local elements interact nonlinearly and are pooled. Other research using displays containing extended contours has implicated the short-range process, but has never demonstrated global cooperativity. In the first of four experiments, it was shown that under certain conditions of presentation, a short-range motion percept exhibiting apparent global cooperativity can be obtained when collections of randomly located contours are rotated about the center of a display, despite the fact that the displacement of peripheral contours falls outside the normal limit of the short-range process. Experiments 2-4 were conducted to provide further evidence that the observed motion is short-range (i.e., it can be disrupted by illuminating the interstimulus interval or with dichoptic viewing) and that the percept is globally cooperative (i.e., masking the center of the display, where separations between corresponding elements across frames are smallest, results in a decline in the frequency of reports of the short-range percept). Control observations suggest that the effect produced with masks was not due to a decrease in the number of elements in the display. The argument that the display exhibits a short-range process with global cooperativity is further developed.     

Directional information and apparent movement—The apparent movement to apparent simultaneity threshold

This paper reports a study of changes in apparent movement to apparent simultaneity thresholds as a function of the directional information of the second point of light. An earlier paper (Jeeves and Bruner, 1956) reported changes in thresholds from apparent movement to apparent successiveness when the same experimental variable was manipulated. In interpreting the results the authors proposed an hypothesis in terms of “attentional disarticulation.” Brown (1956) commenting on this earlier paper put forward an alternative explanation of the results in conventional informational terms and he predicted the changes in the apparent movement to apparent simultaneity thresholds which should occur if studied under the same experimental conditions. He further showed that his predictions would differ from predictions made on the basis of our own explanation. The results of the experiment reported here uphold the predictions of our own earlier theory and fail to fit those made by Brown. However, in attempting to understand the results from the two experiments considered together, it is suggested that a factor must be included which was omitted from our own earlier explanation but emphasized by Brown. This factor as stated by Brown (1956) is “that the threshold for a discrimination tends to increase with the information content of any discrimination which has to be made concurrently.”     

Interactions between spatial and kinetic dimensions in movement aftereffect

In some conditions, the surface of the test figure on which one sees an aftereffect of movement does not fit with that part of the visual field previously adapted to a movement. Such an effect, called kinetic-figural effect, may be conceived of as resulting from an interaction between two perceptual systems, each one giving specific information: one for the kinetic aspects which are spatially defined, the other for the spatial relationship inside the visual field. Experiments are presented which indicated the validity of a “law of location” for a movement aftereffect, together with some effects of the spatial relationships between adapting and test fields upon the movement aftereffect.     

Temporal characteristics in apparent movement: Omega movement vs. PHI movement

A vertical line stimulus was presented alternately at two positions on an oscillo scope face, with no interstimulus interval. Observation of this stimulus produced haphazard alternation between a number of movement percepts, which were divided into four categories: phi, omega and partial movement, and no movement. Attention to one category did not increase the proportion of time movement in that category it was reported. Proportion of time reported for each category varied differentially as a function of alternation frequency. Upper and lower displacement amplitude limits were measured as a function of frequency for phi and omega movement. Both limits for omega movement differed from those for phi movement. The results imply that phi and omega movement involve separate processing stages in the visual system.     

Directional information and apparent movement

The number of alternative directions that a point of light can take in the apparent movement produced by the successive exposure of two points of light may be considered its directional information. The present experiment is concerned with the relationship between such directional information and the threshold between apparent movement and apparent successiveness, the original hypothesis being that the greater the directional information, the higher the threshold of movement. In fact, contrary results were obtained. Thresholds were obtained under conditions where movement could occur in either eight directions or only in two directions, better and more persistent movement being found under the former conditions. But this result is obtained only when one measures thresholds by an ascending method: increasing the time separation between light points from optimal movement to successiveness. An hypothesis is proposed to explain the findings stated in terms of “attentional disarticulation”.     

Changing-loudness aftereffect following simulated movement: implications for channel hypotheses concerning sound level change and movement.

Listening to a tone changing unidirectionally in sound level causes an illusion of changing loudness in a steady tone afterward. This aftereffect may indicate channels for detecting the feature of change in sound level, which would primarily concern dynamic sound localization. Three subjects, one of whom was the author, participated in this study. The author predicted that opposite adaptation of the ears (the adapting stimulus is heard to move from one ear to the other) should lead to a movement aftereffect. This was not reported by the subjects. However, the subjects did report a changing-loudness aftereffect in a monaural test stimulus, and the characteristics of the changing-loudness aftereffect (such as its magnitude) were consistent with previous data, suggesting a two-stage channel hypothesis: Output from channels for several features, including sound-level change, simultaneously stimulate movement channels.     

Grouping of stimuli and apparent exceptions to the psychological refractory period

When a subject is called upon to respond independently to two stimuli, the second of the two responses is often delayed if the stimuli follow closely on one another, and this has led to the suggestion that in making decisions the human operator accepts and organizes the available input information intermittently in the manner of a discontinuous servo. According to this view two nearly simultaneous stimuli can only be dealt with equally fast if they are grouped into a single decision to respond to both stimuli; otherwise one will have to wait for the attention of the central mechanism until the other has been dealt with. In the present experiment it is shown that delays in the second response are not necessary or invariable, and that the pattern and timing of the second responses when they are performed without delay differ in important respects from those to be expected of grouped responses. It is concluded that the central mechanisms concerned in the response do not possess the limitations that the single channel theory would suggest.     

Position uncertainty and the perception of apparent movement

Two experiments compared the perception of apparent movement when the second of two successive stimuli always appeared in the same position and when it varied randomly between two spatial positions. The results of both experiments showed that foreknowledge of the position of the second stimulus does not facilitate the perception of apparent movement. Experiment 2 also clearly showed that the space-time relationships of Korte’s third law of apparent movement does not depend on foreknowledge of the position of the second stimulus. These findings imply that apparent movement in real time occurs after the second stimulus has been registered by the visual system. It suggests that apparent movement involves a delayed decision mechanism that stores the first stimulus, the interstimulus temporal interval, and the second stimulus, and then impletes a motion compatible with the stimulus information.