Interacting Cache memories: evidence for flexible memory use by Western Scrub-Jays (Aphelocoma californica)

When Western Scrub-Jays (Aphelocoma californica) cached and recovered perishable crickets, N. S. Clayton, K. S. Yu, and A. Dickinson (2001) reported that the jays rapidly learned to search for fresh crickets after a 1-day retention interval (RI) between caching and recovery but to avoid searching for perished crickets after a 4-day RI. In the present experiments, the jays generalized their search preference for crickets to intermediate RIs and used novel information about the rate of decay of crickets presented during the RI to reverse these search preferences at recovery. The authors interpret this reversal as evidence that the birds can integrate information about the caching episode with new information presented during the RI.     

Concurrent disjoint and reciprocal classification by Cebus apella in seriation tasks: evidence for hierarchical organization

We report the results of a 4-year-long study of capuchin monkeys (Cebus apella ) on concurrent three-way classification and linear size seriation tasks using explicit ordering procedures, requiring subjects to select icons displayed on touch screens rather than manipulate and sort actual objects into groups. The results indicate that C. apella is competent to classify nine items concurrently, first into three disjoint classes where class exemplars are identical to one another, then into three reciprocal classes which share common exemplar (size) features. In the final phase we compare the relative efficiency of executive control under conditions where both hierarchical and/or linear organization can be utilized. Whilst this shows a superiority of categorical based size seriation for a nine item test set suggesting an adaptive advantage for hierarchical over linear organization, Cebus nevertheless achieved high levels of principled linear size seriation with sequence lengths not normally achieved by children below the age of six years.     

Absence of color-selectivity in Duncker-type induced visual movement

Using a stationary target and moving field, both consisting of gratings of vertical light and dark bars, Over and Lovegrove (1973) reported that, with monoptic viewing, induced target movement is weaker when the light bars of the two components are different in color. This reduction did not occur for dichoptic viewing, for which the aftereffect was almost negligible. Six experiments are described. The effect of different colors was not confirmed, using a stationary point and moving frame or stationary and moving gratings. Reduced effects for different colors and greatly reduced effects for dichoptic viewing occurred only when there was a stationary boundary to the moving bars of the field grating, as in Over and Lovegrove’s experiment. It is concluded that the effect studied by Over and Lovegrove is not the classical induced movement described by Duncker (1929/1938) but one due to periodic coincidence and noncoincidence of moving and stationary bars in grating patterns. This effect is absent when target and field bars are rendered more distinguishable by different colors.     

Suppressive and enhancing effects of footshock on food-reinforced operant responding following septal lesions in rats.

Effect of septal lesions on suppression of an intermittently food-reinforced lever press by contingent and noncontingent footshock was measured. Rats with septal damage maintained higher response rates than did intact animals under both contingent and noncontingent shock. Furthermore, the difference in suppression produced by the contingent and noncontingent conditions was approximately the same for the experimental and control groups. In a second experiment, performance was measured during counter-conditioning in which the correlation between contingent shock and positive reinforcement was varied. Rats with septal lesions responded at higher rates than did controls. When only reinforced responses were punished, this lesion-induced elevation represented an increase above baseline performance without punishment. This finding suggests that the effect of septal damage on appetitive instrumental performance cannot be due solely to a deficit in response inhibition.     

Mediated generalization in discrimination learning by Rhesus monkeys

Monkeys received discrimination training in which the choice of either a simultaneous or a serial compound of two visual images was rewarded before we assessed the monkeys' conditioned preference for one of the images from the compound. This preference was reduced or blocked if the other image had been associated with reward rather than nonreward prior to compound training. By contrast, the preference was enhanced if the other image was associated with reward rather than nonreward after compound training. The magnitudes of the blocking and enhancement were unaffected by the temporal structure, simultaneous or serial, of the stimulus compound. These results are discussed in terms of the representation of stimulus compounds, the role of within-compound associations, and the similarities between serial and simultaneous visual compounds as processed by monkeys.     

Contingency effects with maintained instrumental reinforcement

In three experiments we investigated the effect on the performance of thirsty rats of varying the instrumental contingency between lever pressing and the delivery of a saccharin reinforcer. In Experiment 1, the subjects performed more slowly in a non-contingent condition, in which the momentary probability of reinforcement was unaffected by whether or not the animals pressed, than in a contingent condition in which the reinforcer was never presented except following a lever press. This was true of performance under both random ratio and interval schedules in which the function determining the probability of reinforcement following a lever press remained the same across the contingent and non-contingent conditions. Experiment 2 demonstrated that instrumental performance was less affected when the contingency was degraded by the introduction of free reinforcers if these reinforcers were signalled. In Experiment 3, lever pressing was reinstated to some degree after non-contingent training by giving non-reinforced exposure to the operant chamber in the absence of the lever. These results suggest that free reinforcers depress instrumental behaviour through a performance mechanism engaged by their ability to support conditioning of the contextual cues.     

Omission Learning after Instrumental Pretraining

Hungry rats were pretrained to press two levers on a concurrent schedule for food pellets. Following either limited or extended pretraining, presentations of a sucrose solution were programmed on a random time schedule while the animals continued pressing on a concurrent schedule for food pellets. Presses on one of the levers-the omission lever-postponed deliveries of the sucrose solution scheduled to occur within a fixed period of time following the press, whereas presses on the other, control lever had no effect on the random time contingency. The animals pressed less frequently on the omission lever than on the control lever following limited pretraining but failed to discriminate between the two levers following extended pretraining. The insensitivity to the omission contingency produced by extended pretraining was due to either the number of presses performed during the initial training or the number of reinforced presses, rather than the number of reinforcers received. Finally, the insensitivity of performance on the omission lever to sucrose devaluation suggests that adaptation tothis negative contingency was mediated by an inhibitory stimulus-response association.     

Book reviews

Gilbert, S. (1986). Pathology of earing. London: Routledge, Kegan Paul. Pp. 246. ISBN 0-7102-0271-7. £14.95

Davey, G. (Ed.). Cognitive processes and Pavlovian conditioning in humans. Chichester: John Wiley & Sons. 1987. Pp. x + 298. ISBN 0-471-90791-X. £32.50.

Boakes, R. A. (1984). From Darwin to behaviourism. Cambridge: Cambridge University Press. Pp. 279. ISBN 0-521-2351-X, £42.50 (hardback); ISBN 0-521-28012-5 £1 9.50 (paperback).     

Age-based discrimination of rival males in western bluebirds

Adaptive social behavior frequently involves discriminating between classes of individuals such as relatives versus non-relatives, older versus younger individuals, or individuals of different status. In the absence of spatial cues, this discrimination may be based on signals that correlate with fitness-related traits (e.g., older or high-status males may sing higher performance songs) or with identity, for example, when receivers distinguish and classify signalers based on their unique signal structure. Here, we examine vocal age-based discrimination in western bluebirds (Sialia mexicana), a North American songbird in which older males have a significant advantage in obtaining extra-pair fertilizations, and therefore pose a significantly higher threat to paternity than younger males. We asked whether western bluebird males showed a higher response to playback of songs of older males compared to younger males relative to their own age. We prepared song stimuli by removing three potential signals of age that have been identified as important in other species: (1) note consistency (which was achieved by playing a single instance of each note repeatedly), (2) note repertoire size, and (3) singing rate (the latter two were equalized across conditions). Even in the absence of these potential signals of age, young males responded more strongly to playback of older males’ songs than to young males’ songs, suggesting that they are able to discriminate between age classes relative to the threat they pose. Further research is required to determine whether this discrimination is based on individual recognition or signal features that are correlated with age.     

Thinking about decisions: An integrative approach of person and task factors

Decisions vary. They may vary in both content and complexity. People also vary. An important way that people vary is how much they think. Some prior research investigating thinking and decision making largely conflicts with most traditional decision theories. For example, if considering an array of products to choose from, thinking more about the alternative's attributes should lead to a better decision. However, some research indicates that thinking more may also lead to focusing on irrelevant aspects of the decision and a less optimal outcome. We propose that this conflict in the literature exists because of a failure to consider the interaction between the individual and the decision task. To test this, we used separate methodologies that enhance or attenuate a person's thinking. In Study 1, we selected people who were especially high or low in need for cognition and had them complete a robust decision-making inventory, which included both complex and simple tasks. In Study 2, we manipulated participant's level of glucose, which acts as the brain's fuel to enhance or attenuate thinking ability. Both studies provide insight for understanding our central tenant that more thought leads to better decisions in complex tasks but does not influence simple decisions. These findings show how the individual's thinking can interact with the constructive elements of the task to shape decision choice.