William Bevan

Free Recall and Abstractness of Stimuli

The relation of abstractness of stimuli to efficiency of free recall was studied in college and fourth-grade students. Groups were shown a sequence of objects, pictures, and object names and were asked to recall what they had seen. Recall tests were conducted either immediately after presentation of the stimulus-sequence, after 24 hours, or after 1 week. Objects were recalled more frequently than pictures, and pictures more frequently than words. Adults performed better than children, except in the case of objects.

Objective measurement of dominance control in binocular rivalry

Six male as attempted to identify stimuli superimposed on either of two dichoptically viewed rivalry patterns. Ability to influence dominance switches was confirmed with this objective procedure, by reason of a decreased error rate (1) with 3-sec advance knowledge as to which pattern would receive a test stimulus, and (2) with knowledge that an 83% majority of all stimuli would be presented in a given field. However, even when test stimuli were self-initiated, dominant-field and suppressed-field scores were not close to the error rates predicted on the basis of monocular levels and of random guessing, respectively, indicating either misjudgments of pattern dominance or, more likely, a failure of the dominant field to totally suppress its opponent.

Chromatic relationships in metacontrast suppression

Total masking of a colored disk in the Werner disk-ring paradigm was found to be a function of the interaction between its color and the color of the ring that followed it. Suppression occurred most frequently when disk and ring hues were identical, least often when complementary hues were paired, and with intermediate frequency when hues were different but noncomplementary. Results were consistent with predictions from simultaneous color contrast, and support integration theories of metacontrast.

Does context influence the shape of a perceptual scale

Effects of backgroun reflectance on the shapes of scales of lightness were investigated in two experiments. In Experiment I, 25 Ss compared similaritiesofpairs ofgray chips that were viewed against black, gray. or white backgrounds. In Experiment 2, 33 Ss positioned a series of gray chips, viewed against a white, gray. or black background, so that the distances between successive chips represented the perceived differences in lightness between them. The results of both studies indicated that scale shape was influenced by background. The nature of the effect was that interstimulus differences in the region of a background were enhanced relative to interstimulus differences far from a background.

Effects of varying length of stimulus series and response scale upon response latency, response uncertainty, and transmitted information

A 3 by 3 orthogonal design was employed t o study the interrelations among response latency (RL), response uncertainty (ER), and transmitted information Nine groups of Ss judged the size of 5, 20, or 40 projected squares in terms of 5, 20, or 40 response categories. Patterns of change in ER and RL over the three stimulus series were differentially effected by increases in the number of available response categories. The increase from 5 to 20 response categories produced, for successively longer stimulus series, a constantly increasing change in ER; the further increase from 20 to 40 categories produced a contrasting, constantly decreasing change in ER. The same two changes in number of response categories produced the same pattern of change in RL over the 5- and 20-stimulus series but reversed the pattern for the 40-stimulus series. Correlations between ER and RL ranged from .28 to .99 and tended to maximize when number of response categories equaled the number of stimuli. It was relatively low under all conditions. Within the 5- and 20-stimulus series, increases from 5 to 20 to 40 available responses increased RL in a negatively accelerated fashion but did not increase It. Within the 40-stimulus series, the same increases in number of available responses produced an essentially linear increase in both It and RL.

The role of the thematic relationship between focal and contextual stimuli in recall

Three experiments, involving a total of 298 Ss, examined the effect of varying the level of thematic relationship between focal and background stimuli upon recall of the former. In all experiments the focal stimuli were colored pictures of common objects. In Exps. I and III the background stimuli were also pictures of common objects; in Exp. II, they were the names of these objects. In Exps. I and II, tests involved free recall of the class names of the focal stimuli; in Exp. III the background stimuli were used as test stimuli and the required response was the specific name of the focal stimulus. Three levels of thematic relationship—focal and background stimuli were drawn from the same generic class, from a broader related group, or were selected at random—obtained in all experiments. The control condition for Exps. I and II involved presentation of the focal stimuli alone. In Exp. I, the presence of pictorial background stimuli of the same generic class as the focal stimuli had no reliable effect upon the free recall of the latter; however, with background stimuli of lesser relationship, performance was degraded when compared to the control condition. In Exp. II, the presence of verbal background stimuli was found to have no effect upon free recall. In Exp. III, associative recall of specific names was directly related to level of thematic relationship between focal and background stimuli.

Watchkeeping Performance as a Function of Certain Properties of the Viewing Situation

Subjects performed a 90-min. watchkeeping task requiring the detection of a plus sign which occasionally appeared in a matrix of solid circles. Independent variables were: (1) number of stimulus elements in the display; (2) location of those elements relative to the strong contours produced by the physical boundary of the viewing field; and (3) distance of the observer from the display. Average detection time for successive 100-trial blocks revealed the commonly observed vigilance decrement. Detection times were consistently shorter when a wider expanse of surround separated the stimulus array and the physical boundary of the display. They were not influenced by either stimulus density or viewing distance. Accuracy of response was found to deteriorate with an increase in stimulus density but was unaffected by the proximity of the display contours to the stimulus array or, again, by viewing distance.

Temporal factors influencing performance in the missing scan paradigm

Sixty Ss were each presented 120 random sequences of 9 of the 10 digits (0–9); their task on each trial was to supply the missing digit. Two stimulus input rates and two response time limits were combined factorially to yield four experimental conditions. Contrary to expectation, evidence seeming to support the use of a strategy based on the ordinal properties of the stimuli was found only when rapid (1-sec) responses were required, regardless of input rate. It is suggested that this result is most reasonably attributed to the operation of a guessing bias for numbers in the middle of the ordinal sequence. Differences in the constitution of the stimulus series may account for the failure to confirm previous findings of an ordinal strategy.

Structure in the classification of stimuli differing on several continuous attrjbutes

Subjects were requested to sort sets of multidimensional stimuli differing in tint or shade, size, shape, and orientation. Each S received either 64 triangles selected at random from a larger population or 16 selected at random from the sample of 64. On one sort he was allowed to select the number ofcategories to be used; otherwise, he was required to distribute the stimuli among four, five, and six categories, respectively. The predominant strategy proved to be simple abstraction, with incomplete generalization a frequent alternative. On all but a few of the sorts, the sorting principle involved the use of one or a pair of attributes. In addition, Ss displayed a marked tendency toward numerical balance in their sorts and, when allowed to select the number of categories to be used, to limit them to a relatively small number. Imai has previously reported numerical balance and the use of a limited number of categories also to characterize the sorting of stimuli differing on discontinuous attributes. Informational measures proved helpful in describing such aspects of classification behavior as response uncertainty, numerical balance, and efficiency in abstraction.

A Fellowship with Essence

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