A pendulum phenomenon in the visual perception of apparent movement

In setting up an apparatus for studying the phenomenon of apparent movement it was noticed that, when a metronome was employed for making the electrical contacts in the light-circuits, the path of apparent movement between the two lights was curved instead of straight. This deviation could not be attributed to the presence of any distorting structure in the visual field, and an experimental investigation of the conditions of the phenomenon was begun. So far five different display conditions have each been observed by ten or eleven subjects individually. No subject saw more than one condition in the experimental series, and their reports indicate that the following factors, in order of importance, are effective in leading to the perception of curved apparent movement: (1) the shape of the light-stimuli, (2) the regularity of the rhythm of presentation, (3) the gradient of brightening and dimming of the lights and (4) the sound of the metronome in synchrony with the appearance of the lights.

The possible role of past experience in the perceptual process, and the relationship of this “pendular” phenomenon to Johansson's (1950) “wandering” phenomenon and to normal stroboscopic movement, are briefly discussed.     

Early motion processes and the kinetic depth effect

It has been known for over 30 years that motion information alone is sufficient to yield a vivid impression of three-dimensional object structure. For example, a computer simulation of a transparent sphere, the surface of which is randomly speckled with dots, gives no impression of depth when presented as a stationary pattern on a visual display. As soon as the sphere is made to rotate in a series of discrete steps or frames, its 3-D structure becomes apparent. Three experiments are described which use this stimulus, and find that depth perception in these conditions depends crucially on the spatial and temporal properties of the display:

1. Depth is seen reliably only for between-frame rotations of less than 15°, using two-frame and four-frame sequences.

2. Parametric observations using a wide range of frame durations and inter-frame intervals reveal that depth is seen only for inter-frame intervals below 80 msec and is optimal when the stimulus can be sampled at intervals of about 40-60 msec.

3. Monoptic presentation of two frames of the stimulus is sufficient to yield depth, but the impression is destroyed by dichoptic presentation.

These data are in close agreement with the observed limits of direction perception in experiments using “short-range” stimuli. It is concluded that depth perception in the motion display used in these experiments depends on the outputs of low-level or “short-range” motion detectors.     

Experimental disorientation in the horizontal plane

Twenty-eight subjects were examined on a visual matching task for their ability to maintain an orientation with respect to a particular direction in the horizontal plane following a voluntary rotary body movement through 180 degrees. Each subject was examined with respect to eight different directions.

Numerous gross errors occurred when visual information was reduced to the display of an arrow indicating a direction and a second arrow manipulated by the subject. The magnitude and distribution of the errors suggest that, under the conditions of this experiment, visual information as to direction in the horizontal plane is analysed according to the two horizontal dimensions defined by the sagittal and coronal planes of the head. In correcting for the rotary body movement, failure may occur with respect to either or both of these two dimensions. The frequency of a failure to make any correction at all (i.e. 180-degree errors) is consistent with independent failure in each of the two horizontal dimensions.

Failure is markedly more frequent in the fore-aft dimension than in the left-right dimension. It is suggested that this may be explained in terms of the ambiguous spatial significance of vertical disposition on the retina and the possibility of contamination between the two systems of conceptual analysis which identify the vertical and the fore-aft dimensions of visual space.

It is demonstrated that when minimal “landmarks” are provided they tend to be utilized as reference points in attempts to maintain orientation, even when the subject is aware that the “landmarks” are misleading. Such a use of “landmarks” does not suppress the previously mentioned mechanism of dimensional orientation.

The relevance of these results to normal human orientation is discussed.     

Temporal factors in pattern vision

A sequence of uncorrelated randomly patterned visual stimuli (“visual noise”) is normally seen as a field of particles in “Brownian motion.” When each frame of the sequence is followed by a blank flash superimposed on the same region of the visual field, the apparent structure of the noise field is strikingly altered, its form varying with the time interval between frame and flash. At a critical interval, many dots seem to cohere, to form maggot-like objects.

Some of the factors determining this critical interval have been studied. They include the brightness, repetition frequency and exposure duration of the noise field, and the distance of its retinal image from the fovea.

The critical interval for “perceptual blanking” is quite different from that for the “maggot effect,” but the two show a suggestively similar dependence upon the duty cycle of the noise display.

It is of some neurological interest that the phenomenon is not appreciably visible with dichoptic mixing of noise and blank stimuli.     

Variations in reflex blink-rate during visual-motor tasks

The influence of the performance of various tasks on the reflex blink rate has been investigated repeatedly, but the results obtained have been somewhat contradictory. More recently, it has been suggested that the reflex blink rate may be a considerable factor in the accuracy with which visual-motor tasks are performed. The aim of the present experiment was to attempt to obtain further evidence on both these questions.

The experiment was carried out in two parts. The main part was done in the laboratory, while a validating experiment was carried out on the road. In the laboratory, subjects were required t o steer a pencil along a moving track which varied in difficulty. The difficulty of the response was varied by using a direct control on some trials and a velocity control on others. Blink rate, errors, and control measurements were recorded throughout. In the road experiment, cine films were taken of the driver's eyes while driving in heavy traffic and in open country.

The results of both experiments show:

(a) That there are marked individual differences in blink rate, the relative order of which is maintained in spite of variations in the actual blink rate.

(b) That there is no relationship between the accuracy with which a particular individual carries out a task of this sort and his blink rate. The rapid “blinker” is no more and no less likely to be accurate than the infrequeiit I “blinker.”

(c) That the actual blink rate for all individuals varies inversely with the difficulty of the task and the amount of control movement necessary. The blink rate decreases as the necessity for detailed visual control of movement increases. Blink rates when driving a car in heavy traffic, or when steering along an oscillating track, are considerably lower than when driving in open country or when following a straight track.

(d) That the adjustment of the blink rate to the difficulty of the task is achieved not only by an alteration in overall blink rate, but also by a change in the distribution of blinking. The blink rate is approximately constant under constant conditions, but when the task is varying in difficulty, blinking occurs just before and just after periods of maximum difficulty, but is completely inhibited during the periods of maximum difficulty itself.     

Evidence of a single-channel decision mechanism limiting performance in a serial reaction task

An experiment is described in which the subject sat facing a display of two neon bulbs. When the left-hand bulb lit he pressed a key under his left hand, and when the right hand bulb lit he pressed a key under his right hand. The left-hand bulb gave brief flashes at random intervals averaging about 4 sec. The right-hand bulb gave a brief flash at regular intervals of about 4 sec.

The experiment repeats (the author believes for the first time) certain essential conditions of Vince's (1948, 1950) experiments and, following detailed scrutiny of every pair of responses, is taken as evidence for the following statements:—

(a) The response to a signal arriving during the reaction time to a former signal will be delayed by an amount approximately equal to the time elapsing between the arrival of the signal and the end of the reaction time to the former signal.

(b) An exception to this may occur when two signals arrive close together. In this case the two signals may be responded to as a single group.

(c) Delays can be occasioned by the monitoring of responses as well as by reactions to signals.

(d) “Grouping” of signal and monitoring may occur when a signal arrives close to the beginning of the movement made in response to a previous signal.

A survey is made of current theories in this field and suggestions given for further research.     

Temporal structure of letter groups and span of perception

The span of perception for letter groups depends on number of letters presented, length of presentation and structure of the groups. The experiment reported varied the temporal structure of the groups, leaving the total number of letters constant. Groups of 12 letters were presented as a whole or in two or more successive “units.” The total time of presentation was 1-5 sec. In the first experiment each unit was visible until the next appeared, in the second experiment units were visible only during 1/4 sec., although intervals between successive units were kept constant.

The following conclusions emerged:

(a) The visual presence of units did not affect the reproduction for durations over 0.25 sec., except in the 12-letter presentations.

(b) 2×6 letters gave better results than either simultaneous presentation or other divisions; temporal separation was 0.75 sec.

(c) Higher order approximations to Dutch have more influence on 3 × 4, 2 × 6 and 1 × 12 letters than on 4 × 3 and 6 × 2 letters.

(d) A serial order effect exists: central units are reproduced less well than first and last units.

It is suggested that handling a fixed amount of information within a fixed period is limited on the one hand by confusion between simultaneous elements and on the other hand by the interaction between successive units presented too rapidly to allow for proper operation of immediate memory.

The difference between span of perception and span of memory is stressed.     

A study of position habits induced by reward and “frustration”

Predictions from Maier's theory of “frustration”-instigated behaviour have been tested in an experimental situation differing significantly from that in which the theory was propounded yet containing the central element of “frustration”—the insoluble problem.

A water discrimination unit was employed in which the performance of rats would be observed during attacks on insoluble problems, position problems or symbol problems.

Two groups, each containing ten Wistar albino rats, served as subjects. The research design consisted of the following phases: preliminary training, development of position responses, exposure to a symbol-reward problem with 50 per cent, punishment and exposure to a symbol-reward problem with 100 per cent, punishment. The design differed for the two groups only at the phase in which the position responses were established. During this phase one group was exposed to a position-reward problem and the other to an insoluble problem.

Position responses were established as frequently under position-“frustration” (position stereotypes) as under position-reward (position habits) conditions. Position stereotypes were more rigid—more resistant to extinction—than position habits under conditions of 50 per cent, punishment. Position stereotypes were as readily extinguished under 100 per cent, punishment as were position habits under 30 per cent, punishment.

The first two observations conform to predictions made from Maier's theory. The third does not. That is to say, not all situations containing the basic elements of “frustration” give rise to stereotyped behaviour patterns which are as rigid or “fixated” as Maier's theory would predict. It is a reasonable hypothesis that the characteristics of stereotyped responses established in certain “frustration” situations may be described adequately in terms of conventional learning principles without the necessity of resorting to a distinction between “goal-motivated” and “frustration-instigated” behaviour.     

Phenomenal causation at a distance

The aim of this research was to study the finding by Michotte, that a moving object A can apparently produce movement in a projectile B without making contact with it.

The experiments confirm the existence of a causal impression of “pushing at a distance,” but they demonstrate that the greater the distance the smaller the chance that this impression will occur.

When it does, in fact, occur, it has the same characteristics, and is associated with the same experimental conditions, as the impression of “pushing with contact.”

Temporal continuity must obtain between the stopping of the moving object and the starting of the projectile; this refutes any theory positing that there is a “passage” of movement from one object to the other. The effects of differences in speed of movement, whether absolute or relative, are similar in both instances.

In general, however, it appears that distance slightly accentuates the segregation of the movements and that the temporal and kinematic conditions of integration require to be more favourable in the case of distance, if an impression of pushing is to be given which is as satisfying as that found in the case of direct contact.

The size of the Radius of Action, that is, the extent of the passive phase of the projectile, is of the same order in the two cases.

The results bring out the fundamentally temporal-kinematic nature of the perceptual pattern of pushing. They appear difficult to reconcile with an interpretation based on past experience, but tally with the theory of “Ampliation of Movement” put forward by Michotte. According to this theory the essential point lies in the phenomenal transitory belonging to A (the moving object) of the movement performed by B (the projectile).     

Visual search without eye movement

Two experiments have been made on the problem of visual search using six patterns which were geometrically simple, and familiar to the subject.

In each case the subject's task was to say where, among the complex of patterns, a particular pattern (the “test object”) appeared when the exposure of the whole display was so brief as to prevent scanning by the eyes. He could be informed visually (in Experiment I) or verbally (in Experiment II) which pattern was to be regarded as the “test object.”

In both experiments it was found that foreknowledge of what was to be the test object gave a significantly higher standard of accuracy than knowledge given later. This suggests that something analogous to visual search can occur without eye movements.     

Selective interference during the retrieval of visual images

Twenty-six subjects memorized lists of (low I and high I) noun pairs under imagery or verbal mediation instructions. At recall the subjects were presented a digit (“1” or “2”) either auditorily or visually as an interfering stimulus.

Visual interference was found to selectively affect the retrieval of high I response terms. Also, the retrieval of nouns studied by imagery mediation was found to be selectively disrupted by visual interference.

These results suggest that the qualities of a visual image are retained all the way from image acquisition to retrieval, and that the visual components of images generated at the acquisition stage are probably not lost by subsequent coding processes.     

Information relevance, working memory, and the consideration of alternatives

People routinely focus on one hypothesis and avoid consideration of alternative hypotheses on problems requiring decisions between possible states of the world--for example, on the “pseudodiagnosticity” task (Doherty, Mynatt, Tweney, & Schiavo, 1979). In order to account for behaviour on such “inference” problems, it is proposed that people can hold in working memory, and operate upon, but one alternative at a time, and that they have a bias to test the hypothesis they think true. In addition to being an ex post facto explanation of data selection in inference tasks, this conceptualization predicts that there are situations in which people will consider alternatives. These are:

1. “action” problems, where the alternatives are possible courses of action;

2. “inference” problems, in which evidence favours an alternative hypothesis.

Experiment 1 tested the first prediction. Subjects were given action or inference problems, each with two alternatives and two items of data relevant to each alternative. They received probabilistic information about the relation between one datum and one alternative and picked one value from among the other three possible pairs of such relations. Two findings emerged; (1) a strong tendency to select information about only one alternative with inferences; and (2) a strong tendency, compared to inferences, to select information about both alternatives with actions.

Experiment 2 tested the second prediction. It was predicted that data suggesting that one alternative was incorrect would lead many subjects to consider, and select information about, the other alternative. For actions, it was predicted that this manipulation would have no effect. Again the data were as predicted.     

Frustration and stereotyped behaviour in human subjects

The investigation was designed to show the effects upon behaviour of three different durations of frustration, and two degrees of motivation during the frustrating period. Frustration was induced in 144 subjects by setting them the task of “learning” an insoluble temporal maze; they had to record their responses by pressing on one or other of two morse-type keys. Its effect was measured in terms of:

(1) The time taken to learn a soluble maze introduced, without the subjects' knowing it, by changing the system of “rewarding” responses from one based on chance to one based on the constant repetition of a pattern requiring the responses: Left—Right—Right, for its solution.

(2) The tendency for the subjects to show stereotypy of behaviour by responding on the same key for a number of trials in succession without reaching a solution.

(3) The pressure exerted on the response keys, which was taken to be a measure of vacillation.

Predictions that the time taken to learn the soluble task, and the stereotypy, would increase in direct relation to the duration of the frustrating period and the degree of motivation were tested.

It was found that, while there was an immediate increase in both the time taken to learn the soluble task and the stereotypy after a short period of frustration, a point was reached under conditions of prolonged frustration after which no further increase occurred and some adjustment to the situation was shown.

Some confirmation of the effect of increase in motivation in the direction predicted was obtained in all cases, but the differences were not statistically significant. The rankings of the subjects according to the time taken to learn the soluble task and the degree of stereotypy were found to be closely correlated. A definite tendency towards increased vacillation of response was seen in many of the records during the period when frustration might have been expected to have been at its peak.

These findings are discussed in relation to Maier's theory of frustration and to Selye's concept of a “general adaptation syndrome.” The latter theory is more suitable for the interpretation of the results of the present investigation.     

On the tunnel effect

The experiments described in this paper consist of presenting observers with two similar objects in successive movement in the same plane but of which the end of the first and the beginning of the second are hidden by a screen (tunnel). Under proper experimental conditions the impression received is one of continuous and uniform movement by a single object passing behind the screen.

The hidden phase of this movement assumes all of the characteristics of true, visible movement for its entire extent, and any lengthening of the duration of the invisible phase gives the impression of a momentary halt behind the screen at a definite point. A modification of the position or of the relative orientation of the visible portions of the trajectory influences the apparent form of its invisible portion. This form can be made to assume the aspects of complicated curves which are sketched and described by different observers with remarkable consistency.

All these phenomena are dependent upon the objctive conditions: the speed of the objects while they are visible, the length of the tunnel, the duration of the invisible phase, the relative position of the visible portions of the trajectory; and they vary systematically with these conditions. As one or other of these conditions is varied, the impression of continuity may give way to one of a simple succession of independent movements.

It is thought that the absence of sensory qualities justifies the use of the term “amodal data” to describe the way in which the hidden movement phase makes itself known to the observer. These “amodal data” form the bridge between the modal phases and become an integral part of the total sensory experience. These properties are determined by the nature of the complex system of excitations in the same way as those of the modal phases and one can thus consider this amodal aspect of the combined experience as a truly perceptual phenomenon.     

Method of serial extrapolation

A psychophysical procedure is proposed for measuring a subject's power of discerning “lawfulness,” “regularity,” “invariance” in a stimulus sequence. The task consists of supplying the next term in a given series. The method is tested by applying it to a visual series consisting of lines subdivided in geometric progression. The effect upon accuracy of judgement is investigated by varying the settings of the stimulus, in particular the rate of increase or gradient of the series and the number of segments given prior to extrapolation, and of presenting the next-but-one position in the series, thereby converting the task into one of interpolation. Where possible, quantitative predictions are made concerning these variables on the basis of certain explicit assumptions.

Results show that accuracy decreases, as predicted, as the gradient of the series increases, but does not seem to be affected by adding to the number of terms presented. Interpolation shows a reduction in variable error compared with extrapolation more or less as required by theory. Finally, discrepancies in the findings are discussed with special reference to their bearing on the validity of the method.     

Changes in behaviour associated with a nervous system poison (DDT.)

The main purpose of the investigation was to show that behaviour measures can be used to investigate the effects of those toxic drugs which produce “biochemical lesions” in the nervous system although the nature of the lesions still remains undetermined. The advantages of this approach are twofold. First, a psychological study may help to uncover the initial effects of the drug, and thus provide evidence which may lead to the ultimate understanding of the action of the drug. Second, and of value from the practical point of view, such a method may be used to detect toxicity.

In this study D.D.T. was used. Two experiments were performed on one control and four experimental groups of albino rats. Problem solving behaviour, speed and pattern of locomotion, and reaction to stress involving visual stimuli were observed.

Problem solving behaviour was found to be unaffected by the drug; no changes were found in speed of locomotion, but pattern of locomotion revealed that “ataxia” was one of the initial effects of D.D.T. poisioning. The experimental animals were found to be generally less reactive to “stress”; “hyper-irritability” reported in previous studies being explicable in terms of exaggerated motor responses.

The results obtained on “ataxia” showed that the procedure adopted here could be used to detect chronic D.D.T. toxicity in rats.     

“Handedness” and skill

The variability of handedness with different tasks is discussed. Experiments are described which show under what conditions handedness becomes evident. Tasks involving three different levels of complexity were used. The simplest task measured the accuracy with which a particular pressure could be reproduced in isometric contraction of the flexors of the index finger on each side in 21 female subjects. In the second situation, the maximum speed of making an attempted tapping movement under the same conditions, was measured in ten of the same subjects using the same muscle group alternating with its antagonists. The same ten subjects were also tested on an aiming task which provided the third level of complexity. The results suggest that differences in performance between the two sides only occur where “timing” or the serial organization of muscle activity is required and that such differences may be due to training.

Whether handedness is inherited or acquired is briefly discussed, and a second series of experiments using the same tasks as before were carried out on one female and nine male subjects. In this instance, the first two tests were used on the big toe of each side as well as the index finger. The results confirm that differences in performance between the two sides on these tasks can be adequately explained in terms of usage or training.

The hypothesis that “timing” is therefore important in the learning of any movement where serial muscle contractions arc involved was tested and confirmed in a third experimental series. The consistency of timing of the application of force in turning a crank handle at maximum speed was measured in five male subjects before and after training. The implications of the results are discussed in relation to other researches on skills.     

The imaginaiy questionnaire

The experiment was designed to throw some light on the statistical problems in the analysis of questionnaire data. Previous work (unpublished) suggested that a simple choice response was partially determined by previous responses; and also that the nature of the determination was changed with changing length of series. A “null” experiment was devised in the form of a questionnaire without any questions, and the distribution of responses was studied with respect to the problems formulated.

The observations are discussed in three sections.

In the statistical discussion an alternative meaning to overall association or dissociation is advanced. This: relates association or dissociation to human behaviour in the serial response situation, rather than to qualities of the questionnaire. It is further suggested that association between specific, questions should be tested against the association in the whole questionnaire, and an appropriate treatment is indicated.

The observations depart from statistical randomness in certain ways. Answers made up almost entirely of one form of response are given less often than would be expected. Long sequences of the same type of response are relatively infrequent, and sequences of alternation of response are also rare. As the material is “null” it implies that the human concept of randomness differs from the statistical concept.

An attempt is made to define the human concept of randomness. It appears that a series of responses which has a pattern, or for which the subject can postulate a simple “cause” will not be accepted as random by the human subject. This raises problems of a perceptual and cognitive nature. It also has a bearing on the design of questionnaires. or experiments involving serial responses.     

After-images from retina and brain

The evidence pointing to the retinal origin of after-images is considered. The reports of the occurrence of after-images from visual images of hallucinatory vividness are reviewed.

Experimental results are presented to indicate that a complementarily coloured afterimage may arise following the exposure of the temporarily blind retina to a coloured stimulus.

After-images, or after-effects, from vivid images are described in seventeen persons (mostly possessors of “number-forms”). They are found to move with the eyes and to show, in some persons, a degree of conformity with Emmert's Law which, while considerable, is less than that of after-images of real stimuli. In the case of one “eidetic” subject, the after-images from neither real nor imaged stimuli conformed with Emmert's Law. In some persons, after-images of images occur in complementary colours.

The retinal origin of after-images is affirmed, but that they can occur occasionally as a purely central phenomenon is acknowledged. The possible learned or inherent nature of after-images of central origin is discussed.     

The effect of knowledge of results on learning and performance IV. the direction of the error in very simple skills

Re-examination of the data discussed in previous papers of this series shows a greater tendency toward “overshooting” when the time interval between trials, in some of the experiments, is short than when it is longer. The subject tends to make a bigger movement or exert more pressure with short intervals. This seems to be true with or without visual knowledge of results. On the other hand, with the experiments in which the task was to press a key for a given short interval, the effect was not conclusively shown.

A hypothesis is put forward to explain these results in terms of proprioceptive adaptation.