Eliot Hearst

Detecting and identifying change: additions versus deletions.

The recognition of changes in the features of objects was examined as a function of the nature of the change (additions, deletions, no change). In two experiments we assessed both detection (noticing whether the stimulus had changed) and identification (specifying the exact nature of the change). Both detection and identification were expected to depend upon the subjects awareness of the subsequent recognition tasks while the original stimuli were encoded. In Experiment 1, subjects were not aware of subsequent detection and identification tasks while they initially viewed study slides of the to-be-changed stimuli. During the subsequent presentation of the test stimuli, detection and identification were superior for additions. On the other hand, in Experiment 2 when subjects were aware of the subsequent recognition tasks while viewing each study slide, a detection advantage for deletions obtained. Identification performance depended upon a further factor, whether the features of a stimulus were codable. Only in codable stimuli were deletions easier to identify than additions. The differences between the two experiments in detecting and identifying additions versus deletions are consistent with Tverskys (1977) research that stresses the importance of specifying which representation (the study stimulus or the test stimulus) is the subject of comparison in the comparative judgment.

Conditioned approach-withdrawal behavior and some signal-food relations in pigeons: Performance and positive vs. negative “associative strength“

The location of pigeons was monitored during illuminations of a key (CS) presented in a positive, zero, or negative relationship with food for different groups of subjects. Birds approached a signal positively correlated with food and withdrew from a negatively correlated signal. When the probability of food in the absence of CS was increased from 0 to .2 while the probability of food during CS remained constant at .4, approach to CS declined. When the probability of food during CS increased from 0 to .2 while the probability of food in CS absence remained constant at .4, withdrawal from CS declined. No consistent approach or withdrawal appeared when the probability of food was the same (.4) during the presence and absence of CS. Our approach-withdrawal assay of positive and negative associative strength, which allows trial-by-trial measurement of overt performance during excitatory or inhibitory conditioning, was used to assess several predictions of the Rescorla-Wagner model of Pavlovian conditioning.

Man and machine: Chess achievements and chess thinking

A skillful human chessplayer usually achieves the title of chessmaster by the time he is 20 years old, after five or six years of relatively serious devotion to the game. Chronologically at least, computer chess is about as old as the typical new chessmaster; computers first played complete games in 1957 and they have been participants in tournaments with human beings and fellow computers since 1966. Despite much discussion, research, revision, and competition in subsequent years—and despite contrary claims by some computer scientists—the chess programs of 1976 are not much stronger than those of 1966. A human chess enthusiast would have long since abandoned his quest for a master’s or expert’s rating if he had progressed at the snail’s pace displayed by his computer counterparts. Rather than being “barred from competition” in serious tourneys, today’s computer chessplayer would be welcomed as “just another duffer” by most of the competitors.

Temporal location of unsignaled food deliveries: Effects on conditioned withdrawal (inhibition) in pigeon signtracking.

Standard models of Pavlovian conditioning neglect local effects of unsignaled unconditioned stimuli (USs) on learning and performance. Using the approach-withdrawal behavior of pigeons toward keylights as conditioned stimuli (CSs), the authors varied the specific times (5-110 s) that USs occurred before or after a CS. Withdrawal from a CS generally increased as the time between a US before and/or after the CS was lengthened. Combinations of 2 distant USs produced more withdrawal from the CS than either US alone, whereas combinations of a distant and a nearby US yielded behavior intermediate between that for either US alone. Postacquisition retardation tests supported similar conclusions. Based on the temporal isolation of CSs and USs, a tentative model was offered to summarize these data. The results and the model suggest that a more molecular, possibly perceptual approach to Pavlovian excitation and inhibition is needed.

The feature-positive effect in pigeons: Conditionality, overall predictiveness, and type of feature

Two experiments examined variations of standard visual discrimination arrangements in which pigeons typically perform much better when a distinguishing feature appears on reinforced (featurepositive) than on nonreinforced (feature-negative) trials. In Experiment 1 the feature was continuously present on the response key during intertriai intervals as well as during the appropriate type of discrimination trial. Although retarded in its appearance, a strong feature-positive superiority did occur. In Experiment 2 the feature and common cues were reversed in function from those in conventional procedures; a small white square was common to all trials, and the distinctive element involved illumination of the key with a green color. Nevertheless, a significant feature-positive superiority was found, although excellent performance was achieved rapidly for both groups. The results suggest that the conditionality versus nonconditionality of the two discriminations and the feature’s overall positive predictiveness of food are not crucial in producing superior discriminative performance in the feature-positive case.

Generalization gradients around a formerly positive S

After mastering a successive discrimination between a blank key (S+) and a vertical line (S−), two groups of pigeons were tested for line-tilt generalization in extinction. The vertical line had always been associated with nonreinforcement of keypecking in one group, but for the other group it had served earlier as a stimulus associated with reinforcement. All Ss in both groups yielded gradients with a minimum at the S− value, but the latter group made appreciably more responses during testing. Further generalization tests, conducted with reinforcement at all line-tilt values, suggested other differences between the groups.

Psychology at Indiana University: From Bryan to Skinner

Indiana University is the location of the oldest continuing psychology laboratory in America. William Lowe Bryan, a future president of the American Psychological Association, opened the laboratory in January of 1888 and subsequently performed his classic experiments on Morse Code learning there in the 1890s. This article describes the individuals and themes that guided the development of psychology at Indiana in its first 60 years, ending with the chairmanship and activities of B. F. Skinner in 1945–48. The most significant contributions of the members of the department are reviewed and assessed.