Gerbils in space: performance on the 17-arm radial maze.

In Experiment 1 six hungry gerbils received six trials per day on a 17-arm radial maze. During each trial the subjects were allowed to choose freely among the arms, each of which contained a food pellet, until each arm had been visited once or until eight minutes had elapsed. An error was recorded when the subject entered a previously visited arm. The gerbils quickly learned not to re-enter previously visited arms and generally made errors on fewer than 15% of entries, performance comparable to that of the rat and superior to that of other species tested in the radial arm maze. The intertrial-interval duration did not affect accuracy of arm choices during acquisition but did influence asymptotic accuracy. Accuracy did not change systematically over the six trials. A high proportion of arm entries were to nearby arms. Errors occurred most often towards the end of a trial. Odor cues were not important. When the number of trials per day was reduced from six to one, accuracy deteriorated slightly. In Experiment 2 neither the transposition of extramaze cues nor the placement of the maze in a different room had large disruptive effects on accuracy. In Experiment 3 the addition of three explicit intramaze brightness cues aided accuracy, perhaps by permitting the subjects to decompose the large maze into three smaller mazes, although there was no direct evidence that this was the case. Implications of a number of these results for models of spatial maze performance were discussed.     

DO ELEPHANTS EVER FORGET?1

Three adult female elephants (Elephas maximus) were tested on a light-dark discrimination problem with an 8-yr intertrial interval. The first subject took only 6 min to reach criterion and made only two errors, suggesting remarkable retention. The other two subjects were found to have visual anomalies that would have gone undetected without this research.     

Structure in semantic memory: A probabilistic approach using a continuous response task

In the continuous response (CR) task, the subject is given the name of a familiar category and must respond with category examples within a fixed time limit. The response sequence and the interresponse times are the measured variables. A general model is proposed for performance in the CR task. The time taken to generate a response is identified with the shortest search time from among a set of simultaneous search processes. Each response has a generation probability that is a function of the parameters governing the search process durations. Data involving the category states in the United States are used to test the model. The model accounts for the performance of nearly all individuals in these data.This article is based on a dissertation completed at the University of California-Berkeley in partial fullfillment of the requirements for the Ph.D. degree in psychology. Portions of the article were presented at the joint meeting of the Psychometric and Classification Societies (June 1984) and at the meeting of the Society for Mathematical Psychology (August 1984). The authors wish to thank Barbara Mellers, Juliet Schaffer, Steve Palmer, and Eleanor Rosch for helpful comments.     

Quantification of the effects of chlorpromazine on performance under delayed matching to sample in pigeons.

The effects of four doses of chlorpromazine (dose range 0.5 to 12.5 mg/kg) on performance under a delayed matching-to-sample procedure in pigeons was investigated, using the exponential model of memory (White, 1985). Performance was measured using a bias-free measure of discriminability, log d (Davison & Tustin, 1978), and negative exponential functions were fitted to individual-subject and group data at each dose level. A decrease in matching accuracy was found to be caused by an increase in the rate of forgetting, b, and a decrease in the initial discriminability, log d0. Changes in rate of forgetting and discriminability occurred at doses that had no statistically significant effect on response latency. The exponential model of memory accounted well for the data and provided a useful way of quantifying the effects of chlorpromazine on the processes involved in delayed matching-to-sample performance.     

The temporal–hippocampal region and retention: The role of temporo-entorhinal connections in rats

Results from previous studies suggest that the entorhinal cortex may be involved in mnemonic processes. The present study was carried out to investigate whether disruption of fibre connections between the temporal cortex and lateral entorhinal area may impair retention of a pre-operatively acquired simultaneous brightness discrimination task. The lesion resulted in a severe impairment in retaining the discrimination task (Experiment 1). The retention deficit could not be traced into the hippocampal formation by making perforant path lesions or hippocampal lesions (Experiment 2). The results indicate that the lateral entorhinal cortex is more crucial for reference memory than the hippocampal formation.     

Matching, maximizing, and the behavioral unit: concurrent reinforcement of response sequences.

Pigeons pecked two keys in a probability matching situation in which four two-peck sequences were intermittently reinforced: left-left, left-right, right-left and right-right. In Phase 1, relative reinforcement rate was varied with respect to the first response of a sequence: reinforcers were differentially assigned for left-left and left-right sequences as opposed to right-left and right-right sequences. The second response of reinforced sequences occurred equally on the left and right keys across conditions. In Phase II, relative reinforcement rate was varied for sequences that involve an alternation as opposed to those that did not. The relative outputs of the different sequences matched the relative reinforcement rates for the different sequences in both phases. Relative response rates for key pecks did not always match relative reinforcement rates. The intertrial interval separating responses was varied in both phases; increases in the intertrial interval affected the relative frequency of different sequences. The results demonstrate that response sequences acted as functional units influencing choice and thus support a structural account of choice. At the same time, the matching of relative sequence proportion and relative reinforcement rate supports a matching account.     

Not all information in visual working memory is forgotten equally

To improve maintenance of task-relevant information in visual working memory (VWM), previously encoded, but no longer relevant, information can be suppressed or forgotten. However, it is unclear whether a cue directing attention to a subset of stimuli leads to complete forgetting for non-cued stimuli. The current study utilized a novel method of testing to-be forgotten information to determine if the effectiveness of forgetting differs depending on the type of encoded stimuli. Participants performed a directed forgetting change detection task, and importantly, the changed stimulus could be a novel stimulus or a to-be-forgotten stimulus. Stimulus type (colors, objects, or shapes) was manipulated across two experiments. Results suggest that a cue benefits memory for to-be-remembered information, but performance is not equivalent to never encoding to-be-forgotten information. Furthermore, the type of encoded information impacts the extent of forgetting.     

The effects of empathy on search efforts for missing persons

People have difficulty sighting missing persons, partially because people's limited cognitive resources are required for searching. As a result, people sometimes do not devote resources to searching. This research will examine whether empathy increases the resources devoted to searching and search performance. In Experiment 1, we will manipulate empathy toward a formerly missing person and measure willingness to volunteer to search and actual search performance. In Experiment 2, we will manipulate empathy felt toward a missing person. We will measure the time participants spend studying the missing person's photograph. We hypothesize that participants induced to feel empathy will indicate more willingness to search (Exp 1 & 2), put more effort toward searching (Exp 1), and spend more time studying the photograph (Exp 2) than those not induced to feel empathy. If empathy increases search effort and performance, it could be induced in actual missing persons cases to increase recovery rates.     

On the alleged memory-undermining effects of daydreaming

In three experiments, we examined the memory-undermining effects of daydreaming for (un)related stimuli. In Experiments 1 and 2, we tested whether daydreaming fosters forgetting of semantically interrelated material and hence, catalyzes false memory production. In Experiment 3, we examined the memory effects of different daydreaming instructions. In Experiment 1, daydreaming did not undermine correct recall of semantically interrelated words, nor did it affect false memories. In Experiment 2, we again failed to find that daydreaming exerted memory-undermining effects a. In Experiment 3, no memory effects were obtained using different daydreaming instructions. Together, our studies fail to show appreciable memory-undermining effects of daydreaming.     

The propensity to perceive meaningful coincidences is associated with increased posterior alpha power during retention of information in a modified Sternberg paradigm

There are ample inter-individual differences in the frequency with which people perceive meaningful coincidences. Previous research has identified increased proactive interference, that is a reduced working memory capacity, as one possible mechanism associated with this phenomenon. The present study aimed at extending this finding into the domain of neuroscience, (1) by assessing EEG alpha oscillations during the retention of information, (2) by replicating the behavioral link between meaningful coincidences and proactive interference. In a sample of 52 participants, the behavioral replication was successful. Furthermore, participants who perceived more meaningful coincidences showed higher alpha power increases at parietal-occipital sites, and at the same time, displayed lower alpha power increases at frontal areas, during retention of information. This neurophysiological activation pattern further underlines the assumption that participants who perceive more meaningful coincidences show lower working memory capacities, since increased alpha power at parietal areas reflects a higher load on working memory demands.