Grouping by proximity or similarity? Competition between the Gestalt principles in vision.

The nature of the psychological processes that underlie the Gestalt principles of grouping by proximity and grouping by similarity is examined. Similarity was defined relative to the principles of grouping by common colour and grouping by common shape. Subjects were presented with displays comprising a row of seven coloured shapes and were asked to rate the degree to which the central target shape grouped with either the right or the left flanking shapes. Across the displays the proximal and featural relationships between the target and flankers were varied. These ratings reflected persuasive effects of grouping by proximity and common colour; there was only weak evidence for grouping by common shape. Nevertheless, both common colour and common shape were shown to override grouping by proximity, under certain conditions. The data also show that to understand how the Gestalt principles operate it appears necessary to consider processes that operate within and between groups of elements that are initially identified on the basis of proximity. Whether such groups survive further analysis depends critically on the featural content of the constituent elements.

The supposed effect of interactive imagery in paired associate learning.

Previous experiments designed to investigate the effects of interactive imagery in paired associate learning have included the confounded variable of intralist similarity: Images of objects interacting have corresponded to pairs with different connectives, and images of independent objects have corresponded to pairs with the same connective (the conjunction "and"). For the "different" group of our first experiment, the members of the different pairs were linked by different connectives, most of which denoted an action. For the "same" group, the members were linked by the same connective, usually one denoting an action. For the "and" group, the members were linked by the connective "and". Cued recall by the "different" group was superior to that of the other two groups. Recall by the "same" and "and" groups did not differ. Within the "different" group, recall of "and" pairs did not differ from the recall of "action" pairs with which they had been mixed. In a second experiment, subjects were required to match the members of a pair. Analogous results were obtained. Overall, the findings imply that recall effects that have previously been interpreted as being a result of interactive imagery may be the result merely of variations in intralist similarity.

The representation of objects and their attributes in memory: evidence concerning memory for location.

The general principle is advanced that different attributes of objects (e.g. shape and colour) are more readily associated when they are attributes of the same object than when they are attributes of different objects. Previous studies provide support for the principle, for they have shown that a shape is more readily associated with its own colour than, for example, with the colour of its background. In the present experiments, the principle was applied to the attributes of shape and location. In four experiments it was shown that a shape was more readily associated with its own location than with the location of another object. Differences in contiguity between the presentation of the shape and the location with which the shape was to be associated were controlled for, as were other factors. The results were interpreted as providing support for the general principle stated above. It was suggested that the general principle could be explained by supposing that memory is propositional in format.

The mediation of paired associate recall by representations of properties ascribed to objects in perception and imagination.

Any perceived or imagined object will have various properties: for example, it may be of a particular size, shape, and colour. In this paper it is argued that when two objects are perceived or imagined to be interacting, they are likely, as a result, to have properties that may, in part, mediate paired associate recall. In Experiments 1 and 2 it was shown that if the object to be named in recall has properties that are the same as the object named by the cue, then recall is greater than when the properties differ. In Experiment 3 it was shown that if the object to be named in recall has properties that are relevant to a relation between the two objects, then recall is enhanced, as compared with conditions in which this is not the case. In discussion, it is argued that, by means similar to those operating in these experiments, a representation of properties may contribute to recall in experiments in which subjects use interactive imagery.

The recency effect in the perception of ambiguous figures.

After a failure to obtain a recency effect in the perception of ambiguous figures three experiments were carried out to determine the conditions which govern the effect. It was found that the duration of the stimulus which precedes the ambiguous figure (the most recent stimulus) was important. Also of importance was the interval between the next-to-most-recent stimulus and the ambiguous figure. The effect of manipulating these variables was such that sometimes no recency effect was obtained, implying that their state is sometimes critical for the effect. Variations in the duration of the ambiguous stimulus did not cause the recency effect to vary. Recommendations are made for the demonstration of a reliable recency effect.

Comparing two objects for size after a comparison of one of the objects with other objects.

When shown the names of two objects, subjects determine which object is larger more slowly as the difference in the sizes of the objects decreases. This might result from variations in the time taken to access sufficient information to perform the task; information which crudely specifies size is accessed first and can be used when the sizes differ greatly; information which specifies size on a more finely graded scale must be accessed when they do not. This hypothesis was tested. Subjects shown the names of three objects, determined which object was intermediate in size. Immediately thereafter the name of another object was shown, the task then being to decide whether the object previously judged intermediate was larger than this object. In this second task reaction times increased with decreasing differences in size between the two objects; this increase was smaller, however, when the sizes of the objects in the first task were similar. The results were predicted from the assumption that when the specification of an object's size in terms of fine discrimination is accessed for comparison in the first task it remains available for use in the second task; thus the time normally required for accessing that information in the second task is reduced. Some implications of the results are discussed.

Explaining imaginal inference by operations in a propositional format.

Solving problems by imaginal inference often seems inefficient for an organism that is manipulating propositions. One explanation for the apparent inefficiency is that the problems are being solved not in propositional format by operations in an analogue format. Imaginal inference might then be the most efficient method compatible with the limitations inherent in the analogue format. In the present paper an alternative rationale is given for the use of imaginal inference by explaining how the processes involved in mental problem solving are related to those in perception: it is suggested that the mechanisms used in problem solving have evolved from a perceptual system in which hypotheses about events in the sensory field are generated from an internal representation of the world. This thesis denies that perception is passive and suggests that originally for perception. Acceptance of the thesis implies that the capabilities of a propositional format in problem solving would be limited. This limitation could account for the apparently inefficient use of that format in imaginal inference.

Behavioral contrast as a function of the duration of an immediately preceding period of extinction.

For four pigeons key-peck responding was reinforced on a variable-interval reinforcement schedule in the presence of a vertical white line. When response rates had stabilized a horizontal white line was introduced, in the presence of which reinforcement was not available (extinction). The horizontal line was presented once per session, immediately before the vertical line was presented. The duration of the horizontal line varied randomly from session to session, being either 0 sec (i.e., no presentation), 10 sec, 30 sec, 2 min, 10 min, 40 min, or 120 min. When the horizontal line was present for more than 0 sec, behavioral contrast was obtained in the presence of the following vertical line. Contrast increased with increasing durations of the horizontal line, asymptoting when the horizontal line was present for 40 min.

The role of information in the emission of observing responses: a test of two hypotheses.

Pigeons were trained on a trial procedure in a Skinner box. Each trial began with a fixed-interval schedule. Responding on this schedule produced a stimulus and a delayed trial outcome. The stimulus signalled whether the forthcoming outcome was reinforcement or nonreinforcement. Thus, the response was an observing response. When reinforcement was the outcome on 20% of the trials, response rates in the fixed interval were higher than when reinforcement was the outcome on 80% of the trials. This result is consistent with the hypothesis that observing responses are reinforced by the information associated with the stimulus signalling reinforcement. The result seems inconsistent with the hypothesis that observing responses are also reinforced by the information associated with the stimulus signalling nonreinforcement.

Observing responses and informative stimuli.

Pigeons were trained on a trial procedure. A trial began with the illumination of a pecking key by a white light. After a fixed interval, a key peck could turn the key to one of two equi-probable colors and produce a delayed trial outcome-an equi-probable occurrence of either reinforcement or nonreinforcement. After a trial, the key turned dark and the trial ended. The response could be made into an observing response by correlating the key colors with the outcomes. Response rates in the fixed interval then increased to a level greater than when the colors and outcomes were uncorrelated. In another phase, the response produced only the colors. The trial outcomes occurred some seconds after the fixed interval without a response being required. Correlating the colors with the outcomes again increased response rates. In a second experiment, a further condition was added in which reinforcement was the outcome on every trial. Response rates were lower than when there were equi-probable reinforcement and nonreinforcement outcomes with correlated colors, and about the same as when there were equi-probable outcomes with uncorrelated colors. The results suggest that stimuli providing information about the probability of reinforcement are themselves reinforcing.

Behavioral contrast in chained schedules.

In each of two experiments, the rate of key pecking maintained by a variable-interval food reinforcement schedule was measured, first when that schedule was studied in isolation, and then when it was correlated with the second component of a two-component chained schedule. In the first experiment, the first component of the chained schedule was correlated with a fixed-interval schedule; in the second experiment it was correlated with a variable-interval schedule. In both experiments, behavioral contrast was demonstrated in the second component of the chained schedule. Compared to the rate of responding on the food-reinforcement schedule when it had operated in isolation, the rate of responding on the food-reinforcement schedule when it was correlated with the second component was higher, while the rate on the schedule of the first component was lower. The results are discussed with reference to the determinants of contrast.

Behavioral contrast in one component of a multiple schedule as a function of the reinforcement conditions operating in the following component.

The key pecks of four pigeons were reinforced on a variable-interval 5-min schedule which operated in each of the four components of a multiple schedule, indicated by red, green, yellow, and blue stimuli and presented in such an order that the red stimulus always preceded the yellow and the green stimulus always preceded the blue. After establishing baseline rates, the reinforcement schedule associated with the blue and yellow components was altered so that one was now an extinction schedule and the other was a variable-interval 1-min schedule. In a second experimental stage, the blue stimulus was interchanged with the yellow so that the red stimulus preceded the blue and the green stimulus preceded the yellow. In both experimental stages the response rate in the variable-interval 5-min component that preceded the extinction component was higher than the response rate in the variable-interval 5-min component that preceded the variable-interval 1-min component. The results were discussed in relation to the importance of stimulus ordering in experiments concerned with investigating behavioral contrast.