Aaron P. Blaisdell

Causal Reasoning in Rats

Empirical research with nonhuman primates appears to support the view that causal reasoning is a key cognitive faculty that divides humans from animals. The claim is that animals approximate causal learning using associative processes. The present results cast doubt on that conclusion. Rats made causal inferences in a basic task that taps into core features of causal reasoning without requiring complex physical knowledge. They derived predictions of the outcomes of interventions after passive observational learning of different kinds of causal models. These competencies cannot be explained by current associative theories but are consistent with causal Bayes net theories.

Recovery from blocking achieved by extinguishing the blocking CS

Extinction-induced attenuation of single-phase and two-phase blocking was examined with rats in a conditioned lick-suppression task. In Experiment 1, which compared the effectiveness of single- and two-phase blocking, it was found that single-phase blocking was facilitated by the initiation of training with an A-US trial rather than an AX-US trial. Single-phase (but not two-phase) blocking was attenuated as a result of 200 extinction trials with the blocking stimulus (Experiment 2). Experiment 3 revealed recovery from two-phase blocking after 800 extinction trials with the blocking stimulus. Recovery from both types of blocking was specific to the blocked CS trained in compound with the extinguished stimulus (Experiment 4). This is the first article to report that the blocking deficit can be reversed by extinguishing the blocking stimulus. These results are discussed in light of acquisition models (i.e., retrospective revaluation) and expression models (i.e., the comparator hypothesis).

Beyond the Information Given: Causal Models in Learning and Reasoning

The philosopher David Humes conclusion that causal induction is solely based on observed associations still presents a puzzle to psychology. If we only acquired knowledge about statistical covariations between observed events without accessing deeper information about causality, we would be unable to understand the differences between causal and spurious relations, between prediction and diagnosis, and between observational and interventional inferences. All these distinctions require a deep understanding of causality that goes beyond the information given. We report a number of recent studies that demonstrate that people and rats do not stick to the superficial level of event covariations but reason and learn on the basis of deeper causal representations. Causal-model theory provides a unified account of this remarkable competence.

OVERSHADOWING AND LATENT INHIBITION COUNTERACT EACH OTHER : SUPPORT FOR THE COMPARATOR HYPOTHESIS

In 4 conditioned lick suppression experiments with rats, the combined effects of latent inhibition treatment followed by overshadowing treatment were assessed as a test of the comparator hypothesiss (R.R. Miller & L.D. Matzel, 1988) explanations of overshadowing and latent inhibition. Experiments 1 and 2 confirmed the prediction of the comparator hypothesis that combined latent inhibition and overshadowing treatments attenuate the response deficit produced by either treatment alone. Furthermore, consistent with the comparator hypothesis, posttraining changes in the associative status of the putative comparator stimulus altered responding to the target conditioned stimulus (Experiment 3), and switching contexts between latent inhibition and overshadowing treatments (Experiment 4) eliminated the interaction between the latent inhibition and overshadowing treatments.

Two-item same-different concept learning in pigeons

We report the first successful demonstration of a simultaneous, two-itemsame-different (S/D) discrimination by 6 pigeons, in which nonpictorial color and shape stimuli were used. This study was conducted because the majority of recently successful demonstrations of S/D discrimination in pigeons have employed displays with more than two items. Two pairs of stimulus items were simultaneously presented on a touch screen equipped computer monitor. Pigeons were reinforced for consistently pecking at either thesame (i.e., identical) or thedifferent (i.e., nonidentical) pair of items. These pairs were created from combinations of simple colored shapes drawn from a pool of six colors and six shapes. After acquiring the discrimination with item pairs that differed redundantly in both the shape and the color dimensions, the pigeons were tested for transfer to items that varied in only one of these dimensions. Although both dimensions contributed to the discrimination, greater control was exhibited by the color dimension. Most important, the discrimination transferred in tests with novel colored, shaped, and sized items, suggesting that the mechanisms involved were not stimulus specific but were more generalized in nature. These results suggest that the capacity to judge S/D relations is present in pigeons even when only two stimuli are used to implement this contrast.

Capacity and limits of associative memory in pigeons.

How much information can a brain store over a lifetime’s experience? The answer to this important, but little researched, question was investigated by looking at the long-term visual memory capacity of 2 pigeons. Over 700 sessions, the pigeons were tested with an increasingly larger pool of pictorial stimuli in a two-alternative discrimination task (incremented in sets of 20 or 30 pictures). Each picture was randomly assigned to either a right or a left choice response, forcing the pigeons to memorize each picture and its associated response. At the end of testing, 1 pigeon was performing at 73% accuracy with a memory set of over 1,800 pictures, and the 2nd was at 76% accuracy with a memory set of over 1,600 pictures. Adjusted for guessing, models of the birds’ performance suggested that the birds had access, on average, to approximately 830 memorized picture—response associations and that these were retained for months at a time. Reaction time analyses suggested that access to these memories was parallel in nature. Over the last 6 months of testing, this capacity estimate was stable for both birds, despite their learning increasingly more items, suggesting some limit on the number of picture—response associations that could be discriminated and retained in the long-term memory portion of this task. This represents the first empirically established limit on long-term memory use for any vertebrate species. The existence of this large exemplar-specific memory capacity has important implications for the evolution of stimulus control and for current theories of avian and human cognition.

Temporal Encoding as a Determinant of Overshadowing

Three conditioned lick suppression experiments explored the effects on overshadowing of the temporal relationships of two conditioned stimuli (CSs) with an unconditioned stimulus (US). Assuming overshadowing is maximal when the potential information conveyed by two competing CSs is equivalent, the temporal coding hypothesis predicts that greater overshadowing will be observed when the CSs share the same temporal relationship with the US. Rats were exposed to an overshadowing CS that had either a forward, simultaneous, or backward relationship to the US. The relationship of the overshadowed CSs to the US was either forward (Experiment 1), simultaneous (Experiment 2), or backward (Experiment 3). The greatest amount of overshadowing was observed when both CSs had the same temporal relationship to the US. The data are discussed within the framework of the temporal coding hypothesis and of alternative models of Pavlovian conditioning based on the informational hypothesis.

Integration of spatial maps in pigeons

The integration of spatial maps in pigeons was investigated using a spatial analog to sensory preconditioning. The pigeons were tested in an open-field arena in which they had to locate hidden food among a 4×4 grid of gravel-filled cups. In phase 1, the pigeons were exposed to a consistent spatial relationship (vector) between landmark L (a red L-shaped block of wood), landmark T (a blue T-shaped block of wood) and the hidden food goal. In phase 2, the pigeons were then exposed to landmark T with a different spatial vector to the hidden food goal. Following phase 2, pigeons were tested with trials on which they were presented with only landmark L to examine the potential integration of the phase 1 and 2 vectors via their shared common elements. When these test trials were preceded by phase 1 and phase 2 reminder trials, pigeons searched for the goal most often at a location consistent with their integration of the L→T phase 1 and T→phase 2 goal vectors. This result indicates that integration of spatial vectors acquired during phases 1 and 2 allowed the pigeons to compute a novel L→goal vector. This suggests that spatial maps may be enlarged by successively integrating additional spatial information through the linkage of common elements.

Increased amplitude and duration of acoustic stimuli enhance distraction

Extraneous sounds have a variety of effects on animals; they may interfere with communication, cause physical harm, increase wariness, influence settlement decisions, or they may cause distractions in ways that increase vulnerability to predation. We designed a study to investigate the effects of changing both the amplitude and duration of an acoustic stimulus on distraction in a terrestrial hermit crab (Coenobita clypeatus). In experiment 1, we replicated the key findings from a field result: crabs hid more slowly in response to a silent visual stimulus when we simultaneously broadcast a white noise than they did when in a silent condition. In experiment 2, we altered the noise duration and found that a long noise generated greater latencies to hide than a short noise. In experiment 3, we increased the noise amplitude and found that hide latency increased with higher-intensity auditory stimuli. These experiments demonstrate a variety of stimulus factors that influence distraction. Our results suggest that prey animals could be in greater danger from predators when in an environment with auditory distractions.

Sensory preconditioning in spatial learning using a touch screen task in pigeons.

The authors used a touch screen-based visual-search task to investigate spatial integration in pigeons. First, pigeons were presented with a consistent spatial relationship between compound visual landmarks (LMs) A-X and B-Y, separately. Next, pigeons learned to find a hidden goal on the monitor in the presence of LMs A and B. The goal bore a consistent spatial relationship to LM A, but not to LM B. On nonreinforced probe tests, the peak and distribution of responses to LM X suggest that pigeons computed a novel X-goal spatial relationship on the basis of X-A and A-goal spatial vectors. Responses to LM Y, however, revealed no evidence of spatial integration. These results replicate and extend those of A. P. Blaisdell and R. G. Cook (2005) using an open-field task.