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.     

A further study of the pendulum phenomenon

A first series of experiments had demonstrated certain conditions eliciting or inhibiting a “pendulum” phenomenon in the visual perception of apparent movement. The present study consists of five further variations designed to show more clearly conditions of occurrence and non-occurrence of this type of movement. The main findings are:

(i) Altering the axis of display to vertical significantly reduces the frequency of pendular-movement perception;

(2) Altering the position of metronome from behind to the side of the visual display, gives results almost identical with those where the metronome was inaudible, but, when the metronome is illuminated in this position, all forms of movement perception are reduced, and no pendular movement is reported.

The results for all the ten conditions, including the five of the first series are summarized, and the following possible factors are discussed: past experience, physiological nystagmus, and intervening adaptation. All three may be required to account for the perceptual phenomena under investigation and the dichotomizing of explanations into “experiential,” or “physiological,” appears to be arbitrary and inconsistent with the complexity of the observed facts.     

Forward, backward and combined masking: Implications for an auditory integration period

Auditory temporal psychometric functions were obtained for forward masking, backward masking, and for combined forward and backward masking for the case of an impulsive signal in white noise. Temporal psychometric functions show a large interaction between forward masking and backward masking when evaluated against an independence model of performance. The results are not consistent with the concept of a sharp rectangular temporal integrating period (“moment”) to account for the interaction.     

Visual imagery and verbalization with simple tachistoscopic displays

Two experiments, designed to compare the perception and retention of tachisto-scopic displays of four block capital letters and four simple “nonsense” figures are described. The results show that the letters were much better remembered and suggest that this was mainly due to the ease with which they were verbalized. The nonsense figures usually gave rise either to rapidly fading “iconic” images, or to an unstable kind of mixed imagery which was difficult to describe or remember, but in which inadequate verbalization was often a source of error. Subsidiary experiments illustrate the importance, not only of verbalization, but also of symmetry and simplicity in remembering visual display.     

Divided attention, order of report and responses to immediately successive signals

Two effects, “divided-attention” and “order of report”, are operationally denned. Their relative contributions to the reduction in efficiency which accompanies the recognition of difficult nonverbal signals, presented simultaneously, is considered. Experiment I evaluated the two effects in the absence of a fixed order of report and emphasis instructions, confounding features of previous studies. The results showed: an overall impairment of performance with simultaneous signals; a contribution of both effects to the decrement, with a suggestion of the primacy of the “order of report” effect; and a significant interaction between the latter effect and modality, such that visual signals showed the greater effect. Experiment II using similar signals tested the assumption that simultaneity of presentation is a necessary condition for obtaining reduced efficiency with multiple signals. The assumption was only partially confirmed, a significant decrement in performance occurring only for the second of two successively presented signals. Similarities between the two sets of results are noted, as well as between these and modality differences obtained with verbal materials. Two possible accounts of the data are proposed, one based on “input”, the other on “storage” models of divided-attention. The hypothesis that subjects report the most clearly perceived signal first is rejected as an independent explanation.     

An experiment in psoblem solying

Trial-and-error problems are described in terms of “stimulus” difficulty, which is a measure of the number of possible modes of response left to the individual when all the information given is taken into account; and “phenomenal” difficulty, which is a measure derived from the individual's performance. An experiment is described in which three types of problem were presented to human subjects. In all three problems the stimulus difficulty was calculable, stage by stage, in the solution. The problems differed in this stimulus difficulty and also in the qualitative nature of the information provided—from unequivocal to conditional. It is shown that the qualitative difference of the nature of the information bears most relationship to phenomenal difficulty. Some observations are made on the modes of solution adopted, and further experimental work is suggested.     

Interocular Delay Produces Depth in Subjectively Moving Noise Patterns

Brief apparent motion sequences were introduced into a dynamic visual dot display by spatially shifting selected dots between successive frames. This causes the display to look as if it is drifting continuously in one direction. When such a display is observed with an interocular delay the drifting dots appear to be displaced in depth, even though there is no conventional retinal disparity in the display. We found that the magnitude of this depth shift increased with the duration of the apparent motion sequences. With sequences of five or more frames duration the depth effect was very similar to that which would have been predicted with a continuously moving target. With briefer sequences the size of the depth effect decreased rapidly. We suggest that apparent motion cascades form the basis of Tyler's dynamic visual noise stereophenomenon, and we question his “random spatial disparity” hypothesis.     

Reversal learning by fornix-transected monkeys

Experiment 1 examined visual reversal learning and in Experiment 2 monkeys were trained to criterion in a serial reversal set between “FR” and “DRO” response requirements. In both cases impairments were observed in fornix-transected monkeys. These results are discussed in connection with previous findings that in serial reversals damage to the hippocampal system in monkeys causes a deficit in spatial but not in visual learning. A unified account is proposed.     

Conceptual models and task representation in using a command language

In most cases, there is no direct correspondence between the objectives that users of an interactive device may be led to formulate and the commands that enable them to attain those objectives. In order to set up what Young (1981) calls a “mapping” between the “task and action arenas”, users must (1) reorganize their objectives in order to adapt them to the capabilities of the device and (2) if necessary, combine several commands to reach a given objective. In doing so, they are assumed to rely on a “conceptual model” of the device, a notion whose cognitive status remains to be clarified. In this article, the editing keys of the MS/DOS operating system are taken as an example and described according to two different conceptual models. The links between the task and action arenas, in these two conceptual models and in a third one called the “mixed model”, are analysed in detail. Finally, the performance of three groups of subjects, while editing a line of text, are compared. All three of the dependent variables analysed are shown to vary according to how the objective is assumed to be formulated in the three conceptual models. Some hypotheses are presented concerning the cognitive mechanisms involved in such a situation.     

A study of the effect of structural information and familiarity in form perception

Two experiments were carried out to investigate the influence of structural information and familiarity on the processing of visual forms. Pairs of “well” structured and nameable and “poorly” structured and non-nameable fragmented forms were employed as stimuli. The effects of structure and familiarity were assessed by manipulating the visual hemifield of presentation and the task. In Experiment 1 stimuli were judged as being either in the same orientation or mirror-reversed, a task that does not require high-level semantic information to be processed. Experiment 2 required physically identical forms to be matched, which may use either physical or name information. In Experiment 1 “same” judgements were equivalent for both types of stimuli, and “different' judgements were longer for the “poorly” structured (non-nameable) forms. In Experiment 2 there was little overall difference between “well” and “poorly” structured forms, though response times to “well” structured (nameable) forms were slowed for right-visual-field presentations. It is suggested that familiarity may not be sufficient to provide a perceptual advantage for nameable forms, as the advantage for nameable stimuli was confined to “same” judgements in Experiment 1 and response times were shorter for non-nameable stimuli in Experiment 2. Rather, performance depends upon factors such as the computation of global shape (due to structural properties of collinearity and closure) and on the use of different kinds or representations (physical versus name) in matching.     

An unusual case of after-imagery following fixation of an “imaginary” visual pattern

The case of a healthy normal subject is described in which negative after-images were reported to follow fixation of an “imaginary” pattern. The size of the after-image was measured at various distances and found to agree closely with the size of an after-image induced by fixation of a “real” visual pattern, and to conform roughly with Emmert's Law. No evidence for chromatic after-images was obtained. Two controls were conducted, one indicating that the results could not be attributed to after-images resulting from objective aids used to maintain an “imaginary” pattern of constant size; the other discounting the possibility of the subject's having guessed the correct values. Similar phenomena reported in the early literature are briefly mentioned, and some theoretical implications discussed.     

Attentional Tracking in the Perception of Apparent Motion: Evidence from Sequential Blanking Displays

Perception of sequential blanking displays was studied in a series of three experiments investigating factors that influence whether “shadow motion” or “item motion” is seen in a display. In addition to the duration of the blanking interval (BI) itself, three other such factors were identified: the eccentricity at which the display is viewed, the spacing of items in the display, and the type of motion that subjects are instructed to try to see. It is argued that these and other previously reported results are explicable without the need to invoke any kind of visual integration period. Instead, they are interpreted in terms of a first-order system of automatic luminance detectors and a second-order tracking system involving both voluntary and involuntary attention. The relationship of these findings to other recent work in apparent motion and visual attention and to other bistable motion displays is discussed.     

The effect of an irrelevant dimension on “same-different” judgements of multi-dimensional stimuli

Subjects made “same”-“different” judgements of simultaneously presented pairs of visual stimuli which could vary either in shape and colour independently, or in shape alone. In both conditions only shape was relevant to the “same”-“different” judgement. In the former condition “same” and “different” reaction times (RTs) were shorter when the states (“same” or “different”) of the relevant and the irrelevant dimension, colour, were the same. This result is interpreted as support for either a perceptual or a response interference hypothesis. The presence of an irrelevant dimension did not appear to affect differentially “same” and “different” judgements. The need for a re-evaluation of the results from other studies of multi-dimensional stimulus discrimination is discussed.     

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.     

Some errors of perceptual analysis in visual search can be detected and corrected

This experiment tried to discover whether people can correct errors which occur because they incorrectly analyse a display to which they have to respond--whether, in fact, they can correct “perceptual” as well as “motor” errors. In a serial, self-paced visual search task, subjects made one response to indicate that a display of five or nine letters contained either of a pair of target letters, and another response when no target was present. Omission errors were much more common than False Identification Errors, but more of them were corrected. Omission errors were detected and corrected faster than False Identification Errors. Typically omission errors were slow responses while False Identification Errors were fast responses. It is possible to deduce that at least some errors resulting from incorrect analysis of a display can be detected and corrected, probably because of an extension of perceptual analysis during, or immediately after, the time when a response to the display is made.     

On varying the span of visual attention: Evidence for two modes of spatial attention

Three experiments investigated whether subjects could selectively attend to a target item presented in close spatial proximity to a distractor element. Typically, the display consisted of two curved lines, one a target and the other a distractor. The task was to judge the direction of curvature of the target. When subjects attended to a target away from fixation, performance was affected by the presence of a distractor within an area of 1° around the target. In contrast, the distractor did not influence target processing when subjects fixated on the target location. Two modes of visual attention are proposed. When a target is located away from fixation, a “wide” attentional span is employed. With the present stimuli, this led to the detailed processing of items within 1° of the attended position. However, when targets are at fixation a “narrow” span can be adopted, with the result that there is differential processing of attended items even within the formerly critical area.     

What is folk psychology?

Eliminativism has been a major focus of discussion in the philosophy of mind for the last two decades. According to eliminativists, beliefs and other intentional states are the posits of a folk theory of mind standardly called “folk psychology”. That theory, they claim, is radically false and hence beliefs and other intentional states do not exist. We argue that the expression “folk psychology” is ambiguous in an important way. On the one hand, “folk psychology” is used by many philosophers and cognitive scientists to refer to an internally represented theory of human psychology exploited in the prediction of behavior. On the other hand, “folk psychology” is used to refer to the theory of mind implicit in our everyday talk about mental states. We then argue that sorting out the conceptual and terminological confusion surrounding “folk psychology” has major consequences for the eliminativism debate. In particular, if certain models of cognition turn out to be true, then on some readings of “folk psychology” the arguments for eliminativism collapse.     

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.     

The role of familiarity in a face classification task using thatcherized faces

Two experiments are reported to test the proposition that facial familiarity influences processing on a face classification task. Thatcherization was used to generate distorted versions of familiar and unfamiliar individuals. Using both a 2AFC (which is “odd”?) task to pairs of images (Experiment 1) and an “odd/normal” task to single images (Experiment 2), results were consistent and indicated that familiarity with the target face facilitated the face classification decision. These results accord with the proposal that familiarity influences the early visual processing of faces. Results are evaluated with respect to four theoretical developments of Valentine's (1991) face-space model, and can be accommodated with the two models that assume familiarity to be encoded within a region of face space.     

Division of attention between non-verbal signals: All-or-none or shared processing?

Criteria proposed by Broadbent (1971) for deciding between “all-or-none” and “shared” models of divided attention are reviewed and modified. Of the modified criteria, the amount of the reduction in efficiency and the shape of the normalized ROC curve are identified as being diagnostic for deciding between the two models. When applied to the results of two experiments involving the recognition of difficult nonverbal signals, which showed performance on the signals presented together to be significantly worse than performance on the signals when presented alone, both the criteria favour the shared model rather than the all-or-none model. The results of a third experiment with easy signals indicated that artefacts unrelated to attention were unable to account for the reduction in efficiency with difficult signals. It is concluded that the shared model, which assumes some limit to processing capacity, has the widest application to these results and similar findings reported elsewhere. The role of the all-or-none model would appear to be restricted to conditions of extreme informational overload. Further, the movement of noncentral decision criteria and the unequal contribution of the individual dimensions to overall multi-dimension performance demonstrated in the first two experiments, suggest that a reduction in the quality of decision-making may accompany the division of attention, as well as the reduction of information derived from the signals.