Memories of emotional expressions in horses Summary Proops, Grounds, Smith, and McComb (2018) suggest that horses remember previous emotional expressions of specific humans, and use these memories to adjust their behavior in future social interactions. Despite some methodological shortcomings, this study raises important questions on the complexity of social interactions in nonhuman animals, which surely deserve further attention.

Thought control with the dopamine transient Summary Fine-tuning and coordinating neural activity is essential for an efficient brain. Athalye and colleagues (2018) provide important evidence that neural patterns can be streamlined by inducing dopamine transients.

Even bees know zero is less than one Summary Across three elegant experiments, Howard, Avarguès-Weber, Garcia, Greentree, & Dyer (2018) demonstrate that honey bees spontaneously generalize an ordinal rule to empty sets, treating zero as less than other whole numbers. Their findings provide strong evidence that bees have a nonsymbolic concept of zero similar to that found in monkeys and human children, suggesting that this capacity may have important evolutionary significance.

To peck or not peck: Which do pigeons prefer? Abstract Animals are expected to minimize time and effort to reinforcement. Thus, not pecking should be preferred over pecking. However, even if time is held constant, pigeons often peck when it is allowed but not required (e.g., fixed time schedules), but with such schedules pecking may be adventitiously reinforced. In the present experiment, to better compare a schedule of reinforcement that requires pecking with one that requires the absence of pecking, we compared a modified fixed-interval (FI) schedule in which reinforcement follows the first peck after the interval has elapsed and a differential-reinforcement-of-other behavior (DRO) schedule, which requires pigeons to abstain from pecking for a similar interval. The delay to reinforcement was matched on a trial-by-trial basis by yoking the duration of the FI to match the DRO schedule that preceded it. Of 12 pigeons, six preferred the DRO schedule over the FI schedule and six did not show a schedule preference. Those that were indifferent between the schedules apparently had a stronger spatial preference than their schedule preference. Individual differences in the preference of the pigeons may have been related to their behavior during the DRO schedule.

Exploring individual and social learning in jackdaws ( Corvus monedula ) Abstract Information about novel environments or foods can be gathered via individual or social learning. Whereas individual learning is assumed to be more costly and less effective than social learning, it also yields more detailed information. Juveniles are often found to be more explorative than adults. Still under the protection of their parents, this allows them to sample their environment in preparation for later in life. We tested individual and social learning in jackdaws (Corvus monedula) of different age groups in a semi-natural group setting. Juvenile and adult jackdaws differed in their learning propensity. Juveniles spent more time at the test apparatus, were more explorative, and caused the apparatus to open. Almost all the openings at the apparatus matched the demonstrated method. As more observers became available, the juveniles could observe each other. Individuals preferentially watched successful conspecifics and those they could scrounge food from. Lower-ranking individuals tended to watch higher ranking ones; higher ranking individuals preferentially watched conspecifics of similar rank. The control group did not manipulate the apparatus. Due to the lack of this baseline, it was difficult to determine for certain whether the opening technique was acquired via individual or social learning. We conclude that if social learning played a role, the underlying mechanism was most likely local or stimulus enhancement. It is, however, more parsimonious to assume that juveniles were more explorative than adults, and that their opening technique was potentially easier to acquire than the one demonstrated to adults.

Coffee time: Low caffeine dose promotes attention and focus in zebrafish Abstract In this study we investigated the ability of zebrafish to discriminate visual signs and associate them with a reward in an associative-learning protocol including distractors. Moreover, we studied the effects of caffeine on animal performance in the task. After being trained to associate a specific image pattern with a reward (food) in the presence of other, distractor images, the fish were challenged to locate the exact cue associated with the reward. The distractors were same-colored pattern images similar to the target. Both the target and distractors were continually moved around the tank. Fish were exposed to three caffeine concentrations for 14 days: 0 mg/L (control, n = 12), 10 mg/L (n = 14), and 50 mg/L (n = 14). Zebrafish spent most of the time close to the target (where the reward was offered) under the effects of 0 and 10 mg/L caffeine, and the shortest latency to reach the target was observed for the 10-mg/L caffeine group. Both caffeine treatments (10 and 50 mg/L) increased the average speed and distance traveled when compared to the control group. This study confirms previous results showing that zebrafish demonstrate conditioned learning ability; however, low-dose caffeine exposure seems to favor visual cue discrimination and to increase zebrafish performance in a multicue discrimination task, in which primarily focus and attention are required in order to obtain the reward.

Relative reinforcer rates determine pigeons’ attention allocation when separately trained stimuli are presented together Abstract Previous research suggests that organisms allocate more attention to stimuli associated with higher reinforcer rates. This finding has been replicated several times when stimuli are trained together as compounds, but not in other procedures. Thus, the generality of the relation between relative reinforcer rates and divided attention is not well established. Therefore, we investigated whether relative reinforcer rates determine attention allocation when stimuli are trained separately and then encountered together. Pigeons learned to associate two colors and two frequencies of key light on/off alternation with a left or right comparison key in a symbolic 0-s delayed matching-to-sample task. Across conditions, we varied the probability of reinforcement associated with each stimulus dimension during training. After training, we introduced test trials in which a color and flash-frequency stimulus were presented simultaneously. During sample-stimulus presentation in test trials, all pigeons preferred the stimulus associated with the higher reinforcer rate, suggesting that more attention was allocated to that stimulus. Interestingly, such attention allocation did not result in preference for the comparison that matched that stimulus. Instead, all pigeons preferred the comparison that was physically closer to the stimulus associated with the higher reinforcer rate, suggesting that comparison choice was controlled by the location of that stimulus. Nevertheless, overall, our results provide the first evidence that relative reinforcer rates determine divided attention between separately trained stimuli and thus demonstrate the generality of the relation between relative reinforcement and attention allocation. We suggest several avenues for future research to establish further the generality of this relation.

Mental imagery in animals: Learning, memory, and decision-making in the face of missing information Abstract When we open our eyes, we see a world filled with objects and events. Yet, due to occlusion of some objects by others, we only have partial perceptual access to the events that transpire around us. I discuss the body of research on mental imagery in animals. I first cover prior studies of mental rotation in pigeons and imagery using working memory procedures first developed for human studies. Next, I discuss the seminal work on a type of learning called mediated conditioning in rats. I then provide more in-depth coverage of work from my lab suggesting that rats can use imagery to fill in missing details of the world that are expected but hidden from perception. We have found that rats make use of an active expectation (i.e., an image) of a hidden visual event. I describe the behavioral and neurobiological studies investigating the use of a mental image, its theoretical basis, and its connections to current human cognitive neuroscience research on episodic memory, imagination, and mental simulations. Collectively, the reviewed literature provides insight into the mechanisms that mediate the flexible use of an image during ambiguous situations. I position this work in the broader scientific and philosophical context surrounding the concept of mental imagery in human and nonhuman animals.

The role of category density in pigeons’ tracking of relevant information Abstract Prior categorization studies have shown that pigeons reliably track features that are relevant to category discrimination. In these studies, category exemplars contained two relevant and two irrelevant features; therefore, category density (specifically, the relevant to irrelevant information ratio) was relatively high. Here, we manipulated category density both between and within subjects by keeping constant the amount of relevant information (one feature) and varying the amount of irrelevant information (one or three features). One group of pigeons started with low-density training, then proceeded to high-density training, and finally returned to low-density training (Low-High-Low); a second group of pigeons started with high-density training and then proceeded to low-density training (High-Low). The statistical density of the category exemplars had a large effect on pigeons’ performance. Training with high-density exemplars greatly benefitted category learning. Accuracy rose faster and to a higher level with high-density training than with low-density training; the percentage of relevant pecks showed a very similar pattern. In addition, high-density training (in the Low-High-Low group) led to an increase in performance on the more difficult low-density task, an observation reminiscent of the easy-to-hard effect. These results illuminate factors affecting pigeons’ accuracy and tracking of relevant information in visual categorization.

Reversal training facilitates acquisition of new learning in a Morris water maze Abstract Two experiments determined the effect of interference training on subsequent spatial learning in a Morris water maze. Rats first learned that a platform was located in a quadrant marked by landmarks A and B. Different groups of rats either continued or reversed that training. In the reversal condition the platform was opposite to the initially trained quadrant. On test, a new cue, C, was added and the platform was located in the new AC quadrant. Rats that had received the reversal training learned the location of the new platform faster than rats trained with the same platform throughout. In Experiment 2, phase 1 training was conducted by placing the rats on the platforms to ensure that they were located. Experimental rats received a reversal of the platform position in phase 2. A control group received training with both platforms present, and thus had experience with each. When the platform was then located in the new AC quadrant the rats that received reversal training learned the new location faster than those without reversal training. Results are discussed in terms of the effect of interference on the arousal of general attention.