In 3 experiments, rats were required to find a submerged platform located in 1 corner of an arena that had 2 long and 2 short sides; they were then trained to find the platform in a new arena that also had 2 long and 2 short sides but a different overall shape. The platform in the new arena was easier to find if it was in a corner that was geometrically equivalent, rather than the mirror image, of the corner where it had previously been located. The final experiment revealed that hippocampal lesions impaired rats' ability to find the platform in these arenas. The results suggest that rats did not use the overall shape of the arena to locate the platform but relied on more local cues and that the hippocampus plays a role in navigation based on these cues.

Rats were trained in Experiment 1 to find a submerged platform in 1 corner of either a rectangular or a kite-shaped pool. When the walls creating this corner were a different color than the opposite walls, then learning about the shape of the pool was potentiated in the kite but not in the rectangle. Experiments 2-4 revealed that learning about the rectangle can be overshadowed and blocked when information about the wall color indicates the location of the platform. The results mimic findings that have been obtained with Pavlovian conditioning, and they challenge the claim that learning about the shape of the environment takes places in a dedicated geometric module.

Four appetitive Pavlovian conditioning experiments with rats examined the rate at which the discrimination between compounds AY and AX was solved relative to the discrimination between compounds AY and BY. In Experiments 1 and 2, these discriminations were preceded by training in which A and B were continuously reinforced and X and Y were partially reinforced. Consistent with the Pearce and Hall (1980) model, the results showed that the AY/AX discrimination was solved more readily than the AY/BY discrimination. In Experiments 3 and 4, the discriminations were preceded by feature-positive training in which trials with AX and BY signaled food but trials with X and Y did not. Consistent with the Mackintosh (1975) model, the results showed that the AY/BY discrimination was solved more readily than the AY/AX discrimination. These results are discussed with respect to a hybrid model of conditioning and attention.Keywords: partial reinforcement, continuous reinforcement, feature positive, predictive validity, attention, associabilityCentral to many theories of learning is the assumption that variation in stimulus processing determines the degree to which an association between a conditioned stimulus (CS) and an unconditioned stimulus (US) will be modified. Perhaps most influentially, Rescorla and Wagner (1972) proposed that associative learning is determined by the extent to which the CS and the US are processed. According to Rescorla and Wagner, US processing is variable and is a function of the discrepancy between the magnitude of the US and the total associative strength of all stimuli present ( Ϫ ⌺V). Effects such as blocking (Kamin, 1968), conditioned inhibition (Pavlov, 1927), and the influence of degrading the contingency between the CS and US (Rescorla, 1968) were all cited as phenomena that supported the notion that learning is influenced by variations in US processing. In contrast, processing of the CS (␣) was assumed to be fixed and determined by the physical properties of the CS. Although sympathetic to the idea that CS processing, or attention, 1 may vary as a consequence of experience , no attempt was made to formalize this mechanism.Since the publication of the Rescorla-Wagner (1972) model, however, there has been considerable interest in the idea that CS processing, like US processing, varies as a consequence of learning, and efforts have been made to specify the conditions under which this variation takes place. Two theories, in particular, have come to dominate the study of CS processing. The first, by Mackintosh (1975), proposed that a CS will be processed more when it is a good predictor of a US than when it is a poor predictor of a US (see also Kruschke, 2001;Lovejoy, 1968;Sutherland & Mackintosh, 1971;Zeaman & House, 1963). The second, by Pearce and Hall (1980; see also Pearce, Kaye, & Hall, 1982;Schmajuk, Lam, & Gray, 1996), proposed the opposite: that a CS will be processed more when it is followed by unpredictable events (such as the US) than when it is followed by predictable events. As we sha...

to the rationale, theoretical basis and design of the experiments. Programmed the experiments, collected and analysed the data as part of PhD project. Wrote up the experiments. Peter M. Jones: Co-contributer to the rationale, theoretical basis and design of the experiments. Consulted on analysis and write up as PhD supervisor. Chris J. Mitchell: Co-contributer to the rationale, theoretical basis and design of the experiments. Consulted on analysis and write up as co-author. Andy J. Wills: Consulted on analysis and write up as PhD supervisor.3 AbstractThree experiments were conducted to investigate a possible role for certainty in human causal learning. In these experiments, human participants were initially trained with a set of cues, each of which was followed by the presence or absence of an outcome. In a subsequent training stage, two of these cues were trained in a causal compound, and the change in associative strength for each of the cues was compared, using a procedure based on Rescorla (2001). In each experiment, the cues differed in both their causal certainty (on the part of participants) and size of their prediction error (with respect to the outcome). The cue with the larger prediction error was always the cue with the more certain causal status. According to established prediction error models (Bush & Mosteller, 1951;Rescorla & Wagner, 1972;Rescorla, 2001), a larger prediction error should result in a greater updating of associative strength. However, the opposite was observed, as participants always learned more about the cue with the smaller prediction error. A plausible explanation is that participants engaged in a form of theory protection, in which they were resistant to updating their existing beliefs about cues with a certain causal status. Instead, participants appeared to attribute outcomes to cues with a comparatively uncertain causal status, in an apparent violation of prediction error. The potential role of attentional processes (Mackintosh, 1975;Pearce & Hall, 1980) in explaining these results is also discussed.

Naive male Hooded Lister rats (Rattus norvegicus) were required to find a submerged platform in a right-angled corner between a long and a short wall of a pool in the shape of an irregular pentagon. Tests in a rectangular pool revealed a preference for the corners that corresponded with the correct corner in the pentagon. These findings indicate that rats identified the correct corner in the pentagon by local cues. They contradict the suggestion that rats navigate by moving in a particular direction relative to the principal axis of the shape of their environment.

The ability of rats to solve a discrimination between two objects that differ in length was investigated in five experiments. Using a rectangular swimming pool, Experiment 1 revealed it is easier to locate a submerged platform when it is near the center of a long rather than a short wall. For Experiments 2–4, the objects were black or white panels pasted onto the gray walls of a square pool, with two long panels pasted to two opposing walls and two short panels pasted to the remaining walls. The platform was easier to locate when it was placed near the middle of a long rather than a short panel. This effect was found when the long panels were twice (Experiments 2–4) or four times the length of the short panels (Experiment 4). Experiment 5 demonstrated that rats can solve a discrimination between panels of length 15 and 45 cm more readily than when they are 70 and 100 cm. The results are consistent with the claim that generalization gradients based on stimulus magnitude are steeper for stimuli that are weaker rather than stronger than the stimulus used for the original training.

Hippocampal damage impairs navigation with respect to information provided by the shape of an arena. Recent evidence has suggested that normal rats use local geometric information, as opposed to a global geometric representation, to navigate to a correct corner. One implication of this pattern of results is that hippocampal lesions may impair processing of 1 or more of the local geometric features of an environment. The authors therefore investigated the effects of hippocampal cell loss in rats on navigation to a hidden goal with respect to a variety of local cues in an environment with a distinctive shape. Rats with lesions of the hippocampus were impaired in discriminating a right-angled corner from its mirror image. However, they were able to use cues provided by an acute-angled corner (Experiment 1) or a local polarizing cue (Experiment 2). In contrast, lesioned rats were impaired in discriminating long versus short walls (Experiment 3). Results indicate that the hippocampus plays a role in disambiguating locations by processing (metric) information related to the distance between corners.

The experiments reported here were conducted as part of Tara Zaksaite's PhD. Raw data have been archived using APA's repository hosted by the Center for Open Science at osf.io/ynje9.