A comparative study of memory for olfactory discriminations: Dogs (Canis familiaris), rats (Rattus norvegicus), and humans (Homo sapiens).

Disagreement has arisen in the scientific literature regarding the relative olfactory ability of humans relative to other mammals, specifically canines and rodents. A series of experiments are reported in which memory for multiple olfactory discriminations was measured in dogs, rats, and humans. Participants from all three species learned a sequence of 20 different discriminations between an S + odor and an S- odor. Choice of the S+ odor was rewarded with food for dogs and rats and with positive verbal feedback for humans. After learning the discriminations, an initial memory test was given that involved presentation of all 20 S + and S- pairs. A subsequent mix-and-match test was given in which each S + odor was presented with three different S- odors. The memory tests revealed that dogs were superior to rats and that dogs and rats were superior to humans. The relatively poor performance of humans contrasts with prior findings of high recognition memory for odors followed by slow forgetting. We attribute the low accuracy of humans in our experiments to the requirement that participants had to remember the outcome associated with S + (correct) and S- (incorrect) cues and not just their familiarity. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

An isolation effect in rat spatial memory.

Rats' working memory for locations previously visited and not visited was tested on the radial maze. Trials consisted of a study phase followed by a test phase. In the study phase, rats were forced to visit half the arms on the maze, with the other half of the arms blocked. In the test phase, rats chose among all arms, with food found only on the arms not visited in the study phase. When different patterns of arms visited in the study phase were used, it was found that rats remembered an alternating pattern better than an adjacent pattern or a random pattern and that this effect became more pronounced at longer retention intervals. In addition, rats remembered isolated nonvisited arms in the random pattern that were sandwiched between visited arms better than nonvisited arms that were not isolated between visited arms. Several hypotheses were examined and tested to explain this isolation effect, but no clear theoretical account was found. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Pigeons play the percentages: computation of probability in a bird.

The ability to compute probability, previously shown in nonverbal infants, apes, and monkeys, was examined in three experiments with pigeons. After responding to individually presented keys in an operant chamber that delivered reinforcement with varying probabilities, pigeons chose between these keys on probe trials. Pigeons strongly preferred a 75% reinforced key over a 25% reinforced key, even when the total number of reinforcers obtained on each key was equated. When both keys delivered 50% reinforcement, pigeons showed indifference between them, even though three times more reinforcers were obtained on one key than on the other. It is suggested that computation of probability may be common to many classes of animals and may be driven by the need to forage successfully for nutritional food items, mates, and areas with a low density of predators.

Cognitive flexibility and dual processing in pigeons: Temporal and contextual control of midsession reversal.

Evidence is reported showing that pigeons flexibly use temporal and contextual cues to maximize reward obtained in a midsession reversal task. Pigeons were trained to choose between red and green sidekeys for 60 trials in a session, with choice of one color correct on Trials 1-30 and choice of the other color correct on Trials 31-60 (midsession reversal). Pigeons showed anticipatory errors before reversal and perseverative errors after reversal, and manipulations of the length of the intertrial interval and the point of reversal suggested that pigeons used an internal timer to track the point of reversal. When houselight context cues that signaled the correct choice were presented throughout trials in Experiment 1, choice behavior rapidly came under context control, leading pigeons to rarely make errors and to show no effect of intertrial interval or point of reversal. In Experiments 2 and 3, switches between context and no-context cues occurred among trials. These manipulations revealed that pigeons can readily switch between context control and temporal control of behavior. The internal timer continued to run throughout context trials and could readily be accessed to control choice behavior when a context cue was removed. (PsycINFO Database Record

Release from proactive interference in rat spatial working memory.

A three-phase procedure was used to produce proactive interference (PI) in one trial on an eight-arm radial maze. Rats were forced to enter four arms for reward on an initial interference phase, to then enter the four remaining arms on a target phase, and to then choose among all eight arms on a retention test, with only the arms not visited in the target phase containing reward. Control trials involved only the target phase and the retention test. Lower accuracy was found on PI trials than on control trials, but performance on PI trials significantly exceeded chance, showing some retention of target memories. Changes in temporal and reward variables between the interference, target, and retention test phases showed release from PI, but changes in context and pattern of arm entry did not. It is suggested that the release from PI paradigm can be used to understand spatial memory encoding in rats and other species.

Memory systems in the rat: effects of reward probability, context, and congruency between working and reference memory.

The interaction of working and reference memory was studied in rats on an eight-arm radial maze. In two experiments, rats were trained to perform working memory and reference memory tasks. On working memory trials, they were allowed to enter four randomly chosen arms for reward in a study phase and then had to choose the unentered arms for reward in a test phase. On reference memory trials, they had to learn to visit the same four arms on the maze on every trial for reward. Retention was tested on working memory trials in which the interval between the study and test phase was 15 s, 15 min, or 30 min. At each retention interval, tests were performed in which the correct WM arms were either congruent or incongruent with the correct RM arms. Both experiments showed that congruency interacted with retention interval, yielding more forgetting at 30 min on incongruent trials than on congruent trials. The effect of reference memory strength on the congruency effect was examined in Experiment 1, and the effect of associating different contexts with working and reference memory on the congruency effect was studied in Experiment 2.