Beacon training in a water maze can facilitate and compete with subsequent room cue learning in rats.

In Stage 1 of 4 experiments in which rats completed a water-maze blocking procedure, experimental groups were trained to use a predictive beacon (hanging above, connected to, or displaced from the platform) to find a submerged escape platform in the presence of predictive or irrelevant background cues and in the presence or absence of irrelevant landmarks. In Stage 2, a fixed beacon, landmarks, and background cues all predicted the platform location. A Room Test (landmarks and background cues only) showed that Stage 1 training with a fixed hanging beacon or the moving displaced beacon facilitated Stage 2 learning of predictive room cues for experimental relative to control subjects. In contrast, Stage 1 training with a moving pole beacon interfered with Stage 2 learning about predictive room cues relative to controls, whereas training with a fixed pole or moving hanging beacon had no effect. We conclude that multiple spatial learning processes influence locating an escape platform in the water maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction between piloting and beacon homing by rats in a swimming pool.

In three experiments, rats in a swimming pool were trained to find a submerged platform with a beacon attached to it. For some rats this beacon unambiguously identified the location of the platform; for others the beacon was made ambiguous by placement of an identical beacon in a different part of the pool. Test trials, in the absence of the platform and the beacons, revealed more persistent searching near the original location of the platform if the beacon attached to the platform had been ambiguous. These results show that learning about the location of the platform, with regard to cues that lie beyond the pool, is influenced by the extent to which an animal can find the platform by relying on other cues. The final experiment shows that this interaction between cues is influenced by an animal's prior experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of a beacon on spatial learning based on the shape of the test environment.

In 5 experiments rats were required to escape from a triangular shaped pool by swimming to a submerged platform. The principal group of interest in each experiment received training with a beacon attached to the platform. The purpose of the experiments was to assess if the beacon overshadowed (Experiments 1–4) or blocked (Experiment 5) learning about the position of the platform with reference to the shape of the pool. The platform was located in the center of the pool for the first 2 experiments and in a corner for the remaining experiments. Although there was an overshadowing effect in Experiment 1, the remaining experiments failed to reveal any disruptive influence of the beacon on learning based on the shape of the pool. Moreover, in Experiments 3–5 there was an indication that the beacon facilitated such learning. The results suggest that spatial learning based on the shape of a test environment may not take place in the same way as that based on more discrete landmarks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats repeatedly placed on a hidden platform learn but quickly forget its location.

Retracted July 1989. (See record 1989-35458-001.) Rats were pretrained to escape from cool water by swimming to a platform hidden at a fixed location in a swimming pool. They were then placed a number of times on a platform at a new location in another pool in a new room. Rats placed on the platform subsequently swam to it more quickly than rats that were not placed or rats placed in inappropriate locations. Rats required 10–25 placements on the platform before swimming directly to it on a test trial. An interval of as little as 2 hr between placement and testing eliminated the advantage of previous placement. These results unambiguously demonstrate that rats can latently acquire spatial information, and they disclose some performance features of latent spatial learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative importance of location and feature cues for homing pigeon (Columba livia) goal recognition.

Homing pigeons were raised and trained in two lofts that differed with respect to their color features and location in space. During training, pigeons displayed accurate site preference for a particular loft. When tested for loft preference with the feature cues switched between the 2 lofts, the pigeons returned to the loft that occupied the correct location. In a 2nd experiment, pigeons were trained to find food hidden in I of 4 color bowls (feature cues) located next to a landmark beacon (proximal spatial cue) in a constant location in a room (distal spacial cues). On test trials, pigeons chose the bowl at the correct location in the room if either the color bowl or the beacon was moved by itself but chose the correct color bowl next to the beacon if they were moved together. Together, the data suggest that the importance of location and feature information for goal recognition may be context specific. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholinergic receptor blockade produces impairments in a sensorimotor subsystem for place navigation in the rat: Evidence from sensory, motor, and acquisition tests in a swimming pool.

In Experiment 1, control rats and rats treated with atropine sulfate or atropine methyl nitrate (50 mg/kg) were trained to escape to a visible platform from different starting points in a swimming pool. All groups learned the task by concomitantly developing position responses, by orienting according to room cues, and by orienting to the platform, but probe trials showed that the atropine-sulfate group made more use of the platform as a local cue and made less use of distal cues than did the other groups. The atropine-sulfate group also made fewer searches during acquisition, made fewer searches when the platform was removed on probe trials, and were less responsive to novel cues placed above and around the pool. Swim speed, as estimated by the distance swum on probe trials, was also greater in atropine-sulfate-treated rats. The postulate that rats treated with atropine sulfate preferentially guide swimming by using position responses and local cues was tested in Experiment 2 by comparing their performance with that of control rats in a place task in which the target platform was hidden (no local cues present) and in a similar place task in which the target platform was visible, as was a second incorrect platform that sank when climbed upon (two competing local cues present). Although both tasks were acquired by the control and drugged rats, the two-platform task, as predicted, was comparatively more difficult for the atropine-treated rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How do room and apparatus cues control navigation in the Morris water task? Evidence for distinct contributions to a movement vector.

The present study compared the relative influence of location and direction on navigation in the Morris water task. Rats were trained with a fixed hidden or cued platform, and probe trials were conducted with the pool repositioned such that the absolute spatial location of the platform was centered in the opposite quadrant of the pool. Rather than swimming to the platform location, rats swam in the direction that was reinforced during training, resulting in navigation to the relative location of the platform in the pool and search at the appropriate distance from the pool wall. Pool relocation tests revealed disruptions in cued navigation if the cued platform remained at the absolute location, whereas no disruption was observed if the platform remained at the relative location (same direction). The results indicate that direction holds greater influence than does location and further demonstrate that this observation is not altered by the amount of training or time on the platform. The authors propose that navigation in the water task involves a movement vector in which the distal cues and apparatus provide direction and distance information, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A deficit in ambient visual guidance following superior colliculus lesions in rats.

21 male black-hooded rats were tested for their ability to locate a hidden platform in the Morris swimming pool, in which extrapool cues are required to guide locomotion. At the end of each trial, Ss were either removed immediately or allowed to remain on the platform for 60 sec. As in a previous experiment by the present authors (see record 1984-06177-001), bilateral lesions of the superior colliculus (SC) produced a severe deficit. Permitting the Ss to stay on the platform did not significantly affect performance in either Ss with SC lesions or sham-operated controls. Results indicate that the reduced orienting behavior on the platform observed in the rats with lesions in the previous experiment was not the cause of their navigational impairment. It is concluded that the impairment following SC lesions came about during the swimming itself; therefore, it may be attributed to a disturbance of, or a failure to utilize, ambient vision. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Active preexposure enhances attention to the landmarks surrounding a Morris swimming pool.

Rats were required to swim to a hidden platform in order to escape from a Morris pool, after they had been exposed to the landmarks around the pool by swimming to a platform that had a beacon attached to it. The platform occupied a different place for the test trials than for the preexposure trials. Escape from the pool was facilitated if the landmarks remained in the same place throughout preexposure, but if their positions were changed during preexposure, then subsequent escape from the pool was disrupted (Experiment 2). Escape learning was also disrupted if the rats were placed on the platform for their preexposure treatment (Experiment 3). The results indicate that the associability of the cues around a Morris pool may be enhanced when they are in a stable spatial relationship with the platform throughout each preexposure session. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticholinergic effects on acquisition of place learning in the Morris water task: Spatial mapping deficit or inability to inhibit nonplace strategies?

The role of central cholinergic blockage in spatial learning was examined by testing atropine sulfate-treated (50 mg/kg) rats and saline-injected controls in the Morris water task using training procedures designed to promote the use of a spatial search strategy. First, constraints used in early trials deterred thigmotaxis. Second, an originally oversized hidden platform that nearly occupied the entire pool was effectively "shrunk" into the southwest quadrant of the pool by substituting smaller platforms over trials, a procedure intended to focus attention on the hidden platform in relation to extramaze cues. Task acquisition did not differ between groups, and on the probe trial both groups increased distance and latency and swam preferentially in the previously correct quadrant. Impairments caused by atropine sulfate may be the result of deficits in ability to inhibit nonefficient escape strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrospective revaluation of causal judgments under positive and negative contingencies.

Retrospective revaluation of causal judgments was investigated in a 2-stage procedure. In the 1st stage, compounds of 2 cues were associated with the outcome, whereas in the 2nd stage, a cue from each compound was trained by itself. Associating this cue with the outcome in the 2nd stage had no detectable effect on the causal rating of the other cue from the compound, whereas presenting it without the outcome enhanced the causal rating of the other cue. The retrospective revaluation of the causal rating of these productive cues and also of preventative cues depended on consistent pairing of the cues during compound training, suggesting a role for within-compound associations. These results favor associative accounts of retrospective revaluation that use separate excitatory and inhibitory learning processes rather than a general error-correcting learning algorithm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Repetition blindness, forward and backward.

In these experiments, 2 letters were presented sequentially to the left and right of fixation, followed by pattern masks. Report was cued by spatial location (Experiments 1a, 1b, 2, 4, and 5) or temporal position (Experiments 3, 4, and 5). In all experiments, 2 identical letters on a trial resulted in reduced accuracy of report (repetition blindness; RB) for both the 1st and 2nd presented letters. This decrement was greater for the 2nd letter if subjects expected temporal cues, but tended to be greater for the Ist letter if they expected spatial cues. Analyses of errors and responses on catch trials indicated no bias against report of repetitions, and the repetition decrement did not interact with output order. The data are inconsistent with both type-refractoriness and memory-retrieval accounts of RB. A modified version of N. G. Kanwisher's (1987) token-individuation theory is proposed to account for the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats (Rattus norvegicus) in a water maze learn both an egocentric trajectory and landmarks.

In two experiments we investigated the extent to which rats (Rattus norvegicus) use an egocentric trajectory and landmarks to locate a goal. In Experiment 1 we trained groups to locate the hidden platform in a water maze with either 1 of 3 or 3 of 3 predictive landmarks, and with either a random or fixed egocentric trajectory. A choice test revealed that regardless of the landmark configuration, rats relied on a directional, egocentric trajectory, when it was available, to locate the platform. In Experiment 2 we found that adding four predictive landmarks following training with a constant egocentric trajectory did not alter rats' initial attention to the trajectory. We conclude that the presence of nonpredictive landmarks in a predictive array did not affect the use of landmarks. With a blocking design, rats used initially an egocentric path, then landmarks. These results add to the notion that animals use available spatial cues sequentially. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial learning based on boundaries in rats is hippocampus-dependent and prone to overshadowing.

In three experiments, rats were required to find a submerged platform by referring to the boundaries of a circular swimming pool. In the first experiment, rats with lesions of the hippocampus were impaired at finding the hidden platform, lending support for the proposal that learning to find a goal that is a certain direction and distance from a boundary is dependent upon the hippocampus. Experiments 2 and 3 offered preliminary tests to see if such boundary learning occurred incidentally, irrespective of the presence of a reliable landmark. In contrast to this proposal, a landmark hanging above the platform successfully restricted learning about the location of the platform with respect to the boundary of the arena. The discussion explores the capacity of the hippocampus to encode boundary information, as well as interprets the behavioral results on the basis of an associative learning framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in insulin-stimulated glucose transport and GLUT-4 protein in rat skeletal muscle after training

After running training, which increased GLUT-4 protein content in rat skeletal muscle by <40% compared with control rats, the training effect on insulin-stimulated maximal glucose transport (insulin responsiveness) in skeletal muscle was short lived (24 h). A recent study reported that GLUT-4 protein content in rat epitrochlearis muscle increased dramatically ( approximately 2-fold) after swimming training (J.-M. Ren, C. F. Semenkovich, E. A. Gulve, J. Gao, and J. O. Holloszy. J. Biol. Chem. 269, 14396-14401, 1994). Because GLUT-4 protein content is known to be closely related to skeletal muscle insulin responsiveness, we thought it possible that the training effect on insulin responsiveness may remain for >24 h after swimming training if GLUT-4 protein content decreases gradually from the relatively high level and still remains higher than control level for >24 h after swimming training. Therefore, we examined this possibility. Male Sprague-Dawley rats swam 2 h a day for 5 days with a weight equal to 2% of body mass. Approximately 18, 42, and 90 h after cessation of training, GLUT-4 protein concentration and 2-[1,2-3H]deoxy-D-glucose transport in the presence of a maximally stimulating concentration of insulin (2 mU/ml) were examined by using incubated epitrochlearis muscle preparation. Swimming training increased GLUT-4 protein concentration and insulin responsiveness by 87 and 85%, respectively, relative to age-matched controls when examined 18 h after training. Forty-two hours after training, GLUT-4 protein concentration and insulin responsiveness were still higher by 52 and 51%, respectively, in muscle from trained rats compared with control. GLUT-4 protein concentration and insulin responsiveness in trained muscle returned to sedentary control level within 90 h after training. We conclude that 1) the change in insulin responsiveness during detraining is directly related to muscle GLUT-4 protein content, and 2) consequently, the greater the increase in GLUT-4 protein content that is induced by training, the longer an effect on insulin responsiveness persists after the training.     

The relative influence of place and direction in the Morris water task.

Previous work from our laboratory has demonstrated that rats display a preference for directional responding over true place navigation in the Morris water task. The present study evaluated the range of situations in which this preference is observed and attempted to identify methods that favor navigation to the precise location of the escape platform in the room. A preference for directional responding over place navigation was observed in a wide range of procedures that included providing extensive training (Experiment 1), providing only platform placement experience in the absence of active swim training (Experiment 2), training navigation to multiple platform locations in a moving platform variant of the task (Experiment 3), and explicitly training navigation to a precise location in the room, versus navigation in a particular direction, regardless of the pool's position in the room (Experiments 4-5). A modest preference for navigation to the precise spatial location of the platform was observed when the pool wall was virtually eliminated as a source of control by filling it to the top with water (Experiment 6). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of spatial learning in woodmice (Apodemus sylvaticus) and hooded rats (Rattus norvegicus).

The spatial learning of woodmice and rats was examined in two different experiments. In the Morris place navigation task, the woodmice were slower to escape and took more circuitous routes than did the rats. However, in a special probe trial their accuracy in swimming repetitively through the position of the absent training platform was comparable to that of the rats. In the second experiment, subjects were allowed to escape from a large arena through a hole connected with their home cage. Rats and woodmice learned this task in few trials. In a special trial with no connected hole, subjects of both species showed accurate searching behavior in and around the hole of the training location. However, only the rats developed direct approaches in a systematic manner. These differences are discussed in the contexts of the species specific constraints that might affect the acquisition of direct approaches in a wild species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of passive preexposure on escape from a Morris pool.

In 3 experiments rats were preexposed to the landmarks that surround a Morris pool by being placed on a submerged platform within the pool. They were then required to escape from the pool by swimming to the platform, which was in a location that had not been used during preexposure. Preexposure facilitated subsequent escape from the pool, provided that the platform was not moved during preexposure and the relative position of the landmarks to each other remained constant throughout preexposure. In contrast, if during preexposure the platform was moved from session to session (Experiment 1), or the array of landmarks was altered unsystematically from trial to trial (Experiments 2 and 3), then subsequent learning to escape from the pool was disrupted. These findings suggest that the effects of preexposure to the landmarks in a Morris pool is determined by whether or not they are of relevance for identifying the location of the platform. When they are relevant, then subsequent learning is facilitated, but when they are irrelevant, then subsequent learning is disrupted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Between-cue associations influence searching for a hidden goal in an environment with a distinctive shape.

In Experiment 1 rats had to escape from a kite-shaped pool by swimming to a submerged escape platform in a right-angled corner. The two walls creating this corner were white and the two walls creating the opposite, incorrect, right-angled corner were black. The rats were then trained in a square pool with two white walls forming one corner and two black walls forming the opposite corner. The platform was in the white corner for a consistent group and the black corner for an inconsistent group. A test in an entirely white kite revealed a stronger preference for the correct than the incorrect corner in the consistent but not the inconsistent group. This outcome is attributed to the formation of associations between geometric cues, provided by the shape of the pool, and the color of the walls. The results were replicated in a second experiment in which the walls of the test pool were the same color as the incorrect corner during initial training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned irrelevance: No more than the sum of CS and US preexposure effects?

In the 1st experiment, 1 group of rats (Group Learned Irrelevance [LIRR]) experienced uncorrelated presentations of a noise and shock; a 2nd group (Group Control [CON]) experienced noise and shock in separate phases of training. Six conditioning sessions followed, each consisting of a single noise-shock pairing. Group LIRR conditioned to the noise more quickly than Group CON. The 2nd experiment was identical to the 1st, except that rats were given 6 noise-shock pairings in each conditioning session. In this experiment, Group LIRR learned more slowly than Group CON. These results suggest that learned irrelevance is in part the product of context specificity of latent inhibition, in which the context is the aftereffect of shock presentation. The implications of this for theories of learned irrelevance are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)