Rats' midsession reversal performance: the nature of the response.

The midsession reversal task involves a simple simultaneous discrimination that predictably reverses midway through a session. Under various conditions, pigeons generally both anticipate the reversal and perseverate once it has occurred, whereas rats tend to make very few of either kind of error. In the present research, we investigated the hypothesis that the difference in performance between rats and pigeons is related to the nature of the responses made. We hypothesized that rats could have been better at bridging the intertrial interval by keeping the relevant paw close to the lever while eating, whereas the pigeons had to remove their beak from the response key and insert it into the feeder, thus making it difficult to mediate the response last made. In the present experiment, in successive phases, rats were trained to leverpress or nose-poke on a 40-trial midsession reversal, an 80-trial midsession reversal, and a variable-location reversal. The results showed that the leverpress group acquired the task faster than the nose-poke group, but that both groups reached comparable levels of performance. Thus, the difference in the natures of the responses cannot fully account for the differences in accuracy between rats and pigeons. Additionally, differences in the types of errors made by the two groups suggest that the nature of the response plays different roles in the performance of this task.

Who are the real bird brains? Qualitative differences in behavioral flexibility between dogs (Canis familiaris) and pigeons (Columba livia).

Pigeons given a simultaneous spatial discrimination reversal, in which a single reversal occurs at the midpoint of each session, consistently show anticipation prior to the reversal as well as perseveration after the reversal, suggesting that they use a less effective cue (time or trial number into the session) than what would be optimal to maximize reinforcement (local feedback from the most recent trials). In contrast, rats (Rattus norvegicus) and humans show near-optimal reversal learning on this task. To determine whether this is a general characteristic of mammals, in the present research, pigeons (Columba livia) and dogs (Canis familiaris) were tested with a simultaneous spatial discrimination mid-session reversal. Overall, dogs performed the task more poorly than pigeons. Interestingly, both pigeons and dogs employed what resembled a timing strategy. However, dogs showed greater perseverative errors, suggesting that they may have relatively poorer working memory and inhibitory control with this task. The greater efficiency shown by pigeons with this task suggests they are better able to time and use the feedback from their preceding choice as the basis of their future choice, highlighting what may be a qualitative difference between the species.

Self-regulatory depletion in dogs: insulin release is not necessary for the replenishment of persistence.

It has been hypothesized that self-control is constrained by a limited energy resource that can be depleted through exertion. Once depleted, this resource can be replenished by the consumption or even the taste of glucose. For example, the need to inhibit reduces subsequent persistence at problem solving by humans and dogs, an effect that is not observed when a glucose drink (but not a placebo) is administered following initial inhibition. The mechanism for replenishment by glucose is currently unknown. Energy transfer is not necessary, although insulin secretion may be involved. This possibility was investigated in the current study by having dogs exert self-control (sit-stay) and subsequently giving them (1) glucose that causes the release of insulin, (2) fructose that does not result in the release of insulin nor does it affect glucose levels (but it is a carbohydrate), or (3) a calorie-free drink. Persistence measures indicated that both glucose and fructose replenished canine persistence, whereas the calorie-free drink did not. These results indicate that insulin release is probably not necessary for the replenishment that is presumed to be responsible for the increase in persistence. This article is part of a Special Issue entitled: Canine Behavior.

Suboptimal choice by dogs: when less is better than more.

The less is more effect, an example of an affect heuristic, can be shown in humans when they give greater value to a set of six baseball cards in perfect condition, than to the same set of six perfect cards together with three additional cards each with some value but in fair condition. A similar effect has been reported in monkeys which will eat both grapes and cucumbers but prefer grapes, when they prefer a single grape over a single grape plus a slice of cucumber. In the present experiment, we tested the less is more effect with a nonprimate but social species, dogs. We used dogs that would eat a slice of carrot and a slice of cheese but preferred the cheese. When we then gave them a choice between a slice of cheese and a slice of cheese plus a slice of carrot, most dogs preferred the single slice of cheese. Thus, the less is more effect appears to occur in several species.

Environmental enrichment affects suboptimal, risky, gambling-like choice by pigeons.

Pigeons prefer a risky option with a low probability of a high payoff over a less risky option that results in more food. This finding is analogous to suboptimal human monetary gambling because in both cases there appears to be an overemphasis of the occurrence of the winning event and an underemphasis of the losing event. In the present research, we found that pigeons that were exposed to an enriched environment (a large cage with three other pigeons for 4 h a day) were less likely to show this suboptimal choice behavior compared with typically housed laboratory pigeons in a control group. These results have implications for the mechanisms underlying suboptimal choice by humans (e.g., problem gamblers), and they suggest that a enriched environment may allow for enhanced self-control.

Hungry pigeons make suboptimal choices, less hungry pigeons do not.

Hungry animals will often choose suboptimally by being attracted to reliable signals for food that occur infrequently (they gamble) over less reliable signals for food that occur more often. That is, pigeons prefer an option that 50 % of the time provides them with a reliable signal for the appearance of food but 50 % of the time provides them with a reliable signal for the absence of food (overall 50 % reinforcement) over an alternative that always provides them with a signal for the appearance of food 75 % of the time (overall 75 % reinforcement). The pigeons appear to choose impulsively for the possibility of obtaining the reliable signal for reinforcement. There is evidence that greater hunger is associated with greater impulsivity. We tested the hypothesis that if the pigeons were less hungry, they would be less impulsive and, thus, would choose more optimally (i.e., on the basis of the overall probability of reinforcement). We found that hungry pigeons choose the 50 % reinforcement alternative suboptimally but less hungry pigeons prefer the more optimal 75 % reinforcement. Paradoxically, pigeons that needed the food more received less of it. These findings have implications for how level of motivation may also affect human suboptimal choice (e.g., purchase of lottery tickets and playing slot machines).

Too dog tired to avoid danger: self-control depletion in canines increases behavioral approach toward an aggressive threat.

This study investigated whether initial self-control exertion by dogs would affect behavioral approach toward an aggressive threat. Dogs were initially required to exert self-control (sit still for 10 min) or not (caged for 10 min) before they were walked into a room in which a barking, growling dog was caged. Subject dogs spent 4 min in this room but were free to choose where in the room they spent their time. Approaching the unfamiliar conspecific was the predisposed response, but it was also the riskier choice (Lindsay, 2005). We found that following the exertion of self-control (in comparison with the control condition), dogs spent greater time in proximity to the aggressor. This pattern of behavior suggests that initial self-control exertion results in riskier and more impulsive decision making by dogs.

Sunk cost: pigeons (Columba livia), too, show bias to complete a task rather than shift to another.

The sunk cost effect involves the bias to stay with an alternative because one has already invested resources, even when there is a better alternative available. In a series of experiments, at various points during a 30-peck requirement, pigeons (Columba livia) could choose between completing the response requirement (at a different location in Experiment 1 or the same location in Experiments 3 and 4) and switching to a constant number of pecks. In three experiments, the pigeons showed a bias to complete the pecks already started, even when that required more pecking. We also demonstrated that the bias depended on the initial investment and was not produced merely because the pigeons preferred a variable alternative over a fixed alternative. The deviation from optimal choice suggests that pigeons show a bias similar to the sunk cost effect in humans.

The case of the disappearing bone: dogs' understanding of the physical properties of objects.

To assess dogs' memory for an occluded object, a gaze duration procedure was used similar to one often used with nonverbal infants. A bone shaped dog biscuit was placed behind a solid screen that then rotated in the depth plane through an arc front to back. Dogs were shown either of the two test events. In one event (the possible event), the screen rotated until it reached the point at which it would have reached the bone and then stopped (about 120°); in the other event (the impossible event), the screen rotated through a full 180° arc, as though it had passed through the bone. The dogs looked significantly longer at the impossible event. To control for the differential time it took for the screen to move, for a control group, a bone was placed behind the screen and the screen was rotated either 60° or 120° (both possible events). No difference in looking time was found. To control for the movement of the screen through 120° or 180° when both were possible, for a second control group, the bone was placed to the side of the screen rather than behind the screen and the screen was moved 120° or 180°. Again, no significant difference in looking time was found. Results suggest that much like young children, dogs understand the physical properties of an occluded object. That is they appear to understand that an object (such as a screen) should not be able to pass through another object (such as dog bone).

Self-control without a "self"?: common self-control processes in humans and dogs.

Self-control constitutes a fundamental aspect of human nature. Yet there is reason to believe that human and nonhuman self-control processes rely on the same biological mechanism--the availability of glucose in the bloodstream. Two experiments tested this hypothesis by examining the effect of available blood glucose on the ability of dogs to exert self-control. Experiment 1 showed that dogs that were required to exert self-control on an initial task persisted for a shorter time on a subsequent unsolvable task than did dogs that were not previously required to exert self-control. Experiment 2 demonstrated that providing dogs with a boost of glucose eliminated the negative effects of prior exertion of self-control on persistence; this finding parallels a similar effect in humans. These findings provide the first evidence that self-control relies on the same limited energy resource among humans and nonhumans. Our results have broad implications for the study of self-control processes in human and nonhuman species.

The role of explicit and implicit standards in visual speed discrimination.

Five experiments were designed to investigate visual speed discrimination. Variations of the method of constant stimuli were used to obtain speed discrimination thresholds in experiments 1, 2, 4, and 5, while the method of single stimuli was used in experiment 3. The observers' thresholds were significantly influenced by the choice of psychophysical method and by changes in the standard speed. The observers' judgments were unaffected, however, by changes in the magnitude of random variations in stimulus duration, reinforcing the conclusions of Lappin et al (1975 Journal of Experimental Psychology: Human Perception and Performance 1 383 394). When an implicit standard was used, the observers produced relatively low discrimination thresholds (7.0% of the standard speed), verifying the results of McKee (1981 Vision Research 21 491-500). When an explicit standard was used in a 2AFC variant of the method of constant stimuli, however, the observers' discrimination thresholds increased by 74% (to 12.2%), resembling the high thresholds obtained by Mandriota et al (1962 Science 138 437-438). A subsequent signal-detection analysis revealed that the observers' actual sensitivities to differences in speed were in fact equivalent for both psychophysical methods. The formation of an implicit standard in the method of single stimuli allows human observers to make judgments of speed that are as precise as those obtained when explicit standards are available.

Aging and the depth of binocular rivalry suppression.

Two experiments were designed to examine the effect of aging on the strength of binocular rivalry suppression. To produce rivalry, orthogonally oriented sine-wave luminance gratings were presented dichoptically. The observers were then required either to discriminate the spatial location of a probe spot presented to the dominant or suppressed eye's view or to detect the presence or absence of the probe. The observers in the younger and older age groups exhibited typical rivalry suppression for both tasks (i.e., the probe was more difficult to detect or discriminate when presented to the suppressed eye), but the magnitude of the suppression was significantly larger in the older observers. This increased suppression that accompanies aging can be explained by a reduction in the inhibition produced by the binocular matching circuitry of S. R. Lehky and R. Blake's (1991) model.