Absence of overshadowing and blocking between landmarks and the geometric cues provided by the shape of a test arena

In three experiments rats were required to escape from a pool of water by swimming to a submerged platform. The position of the platform was determined by the shape of the pool, which was either rectangular or triangular. A landmark that was located on the surface of the pool near the platform failed to overshadow (Experiment 1) or block (Experiment 2) learning about the position of the platform with reference to the shape of the pool. Experiment 3 revealed a similar outcome with cues outside the pool, which could be used, in addition to the shape of the pool, to identify the location of the platform. These findings imply that theories of learning that assume that stimuli must compete with each other for the control that they acquire may not apply to spatial learning based on the shape of the environment.     

Potentiation, overshadowing, and blocking of spatial learning based on the shape of the environment

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.     

The effects of pre-exposure on escape from a Morris pool

In two experiments rats were pre-exposed to the landmarks surrounding a Morris pool while they swam to a platform with a beacon attached to it. They were then required to escape from the pool by finding the platform, without the beacon, in a new position. When the platform remained in the same place for each pre-exposure session, but was moved from session to session, then subsequent escape from the pool was more rapid than when the landmarks were not visible during pre-exposure (Experiment 1). But when the platform was moved from trial to trial during pre-exposure, then subsequent escape from the pool was disrupted (Experiments 1 and 2). It is proposed that pre-exposure to the landmark alters the attention that is paid to them, which then influences how readily the landmarks can be used to identify the new position of the platform.     

Latent spatial learning in an environment with a distinctive shape

Four experiments were conducted with rats in order to determine whether being placed on a platform in one corner of a rectangular swimming pool results in latent spatial learning. Rats in Experiments 1-3 received four trials a day of being placed on the platform. During a subsequent test trial, in which they were released into the pool without the platform, the rats exhibited a preference for swimming in the correct corners of the pool (those with the same geometric properties as the corner containing the platform during training), than the two remaining, incorrect corners. This effect was seen when the interval between the final placement trial and the test trial was as much as 24 hr (Experiment 2) and after varying numbers of sessions of placement training (Experiment 3). Experiment 4 revealed that when the test took place in a kite-shaped arena, after placement training in a rectangle, a stronger preference was shown for the corner that was geometrically equivalent to the correct rather than the incorrect corners in the rectangle. The placement treatment is said to result in latent spatial learning based on the development of S-S associations.     

Interaction between locale and taxon strategies in human spatial learning

Three computer-based experiments which tested human participants in a non-immersive virtual watermaze task sought to determine factors which dictate whether the presence of a visual platform disrupts locale learning and taxon learning. In Experiment 1, the visible platform disrupted locale but not taxon learning based on viewpoint-independent and viewpoint-dependent information, respectively. In Experiment 2, taxon learning based on non-geometric cues providing viewpoint-dependent information was disrupted by the visible platform when the cues required relational information to disambiguate them from other cues. Experiment 3 placed participants in an isosceles triangular pool. The presence of the visible platform did not disrupt the encoding of relational information provided by shape of the pool. These results support the notion that geometric cues are encoded in a separate module which is impenetrable to non-geometric cues not creating the shape of the environment.     

Blocking in the Morris swimming pool.

Four experiments demonstrate that spatial blocking is governed by the same principles that govern blocking in Pavlovian conditioning. In the 2nd stage of each experiment, rats escaped from a Morris swimming pool by swimming to a submerged platform with a beacon attached to it. Test trials were then conducted in the absence of the platform and the beacon to assess the extent to which subjects had learned about the position of the platform with reference to the room cues. For the 1st stage of their training, rats either swam to the platform and beacon in the presence of curtains that prevented the room cues from being seen (Experiments 1 & 2), or they swam to the platform and beacon that were moved from trial to trial (Experiments 3 & 4). In each experiment, learning about the room cues in the 2nd stage of the experiment was blocked by the presence of the beacon. This blocking effect was disrupted by changing the appearance of the beacon for the 2nd stage of training or by restricting the amount of exposure to the beacon during the 1st phase of training.     

Evidence of blocking with geometric cues in a virtual watermaze

Three computer based experiments, testing human participants in a non-immersive virtual watermaze task, used a blocking design to assess whether two sets of geometric cues would compete in a manner described by associative models of learning. In stage 1, participants were required to discriminate between visually distinct platforms. In stage 2, additional spatial information was provided by the shape or the color of the walls of the pool. In a test trial, the platforms were removed and the spatial knowledge acquired regarding the position of the platform was assessed. Experimental groups were compared against control groups which did not receive stage 1 training. The unique color of the correct platform, in Experiments 1 and 3, disrupted learning about the colored walls but not the geometry of the pool. In Experiment 2, the correct platform was identifiable from its position within the three platform array. Learning the relative position of the correct platform within the array disrupted learning about its position relative to the geometry of the pool, but not to the colored walls. The results suggest that learning the position of a goal in relation to the geometry of the environment can be blocked but only by an alternative geometric cue.     

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.     

The influence of action on visual search: behavioral response toward stimuli modifies the selection process

In five experiments, we investigated how simple actions (as assessed via a go/no-go task) influence visual search. In Experiments 1 and 2, participants responded (go) when a color name (cue) matched a colored shape (prime), and did not respond (no-go) when they mismatched. Participants then searched a visual array for a tilted line, either embedded within the prime (valid prime) or within a different shape of a different color (invalid prime). For go trials, but not for no-go trials, the validity of the prime influenced search behavior so that faster RTs were observed when the prime was valid as compared with when it was invalid. In Experiment 3, the go/no-go task was based on the shape of the prime. The color of the prime, but not the shape, was re-presented in the search array, and its validity produced a similar pattern as in Experiments 1-2. In Experiment 4, participants responded when the color name and prime mismatched. Reaction times indicated that attentional set had an influence on the validity differences in Experiments 1-3. In Experiment 5, the go/no-go task was based on whether a digit matched a digit appearing within the prime. Go trials produced similar validity effects as observed in Experiments 1-3.     

Spatial learning based on the shape of the environment is influenced by properties of the objects forming the shape

In 3 experiments rats had to find a submerged platform that was located in a corner of a kite-shaped pool. The color of the walls creating this corner provided an additional cue for finding the platform in the shape + color condition but not the shape-only condition. During tests in a pool with walls of a uniform color but no platform, more time was spent in the corner where the platform was originally located after training in the shape + color than in the shape-only condition. The results challenge theories that assume either that learning about the shape of the environment takes place in a dedicated module or that cues compete for the control they acquire over behavior.     

Multiple systems for spatial learning: dead reckoning and beacon homing in rats

Rats homed with food in a large lighted arena. Without visual cues, they used dead reckoning. When a beacon indicated the home, rats could also use the beacon. Homing did not differ in 2 groups of rats, 1 provided with the beacon and 1 without it; tests without the beacon gave no evidence that beacon learning overshadowed dead reckoning (Experiment 1). When the beacon was at the home for 1 group and in random locations for another, there was again no evidence of cue competition (Experiment 2). Dead reckoning experience did not block acquisition of beacon homing (Experiment 3). Beacon learning and dead reckoning do not compete for predictive value but acquire information in parallel and are used hierarchically.     

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).     

Changes in attention to relevant and irrelevant stimuli during spatial learning

Rats were trained in 2 experiments to find a submerged platform that was situated in 1 of 2 of the 4 corners of a rectangular pool with a curved long wall. Different landmarks occupied 2 of the corners on every trial, and the platform was always situated near a landmark. For the place group in each experiment, the location of the platform was indicated by the shape of the pool and stimuli outside the pool (place cues), but not the landmarks within the pool. For the landmark groups, the landmarks, not the place cues, indicated where the platform could be found. During Stage 2, 2 of the place cues were relevant, and 2 of the landmarks were irrelevant, for a new discrimination. The place cues better controlled searching for the platform in the place group than in the landmark group when the place cues had initially been relevant by signaling the presence (Experiment 1) or the absence (Experiment 2) of the platform. The results show that animals pay more attention to relevant than irrelevant cues.     

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.     

Preexposure effects in the spatial domain: Dissociation between latent inhibition and perceptual learning

In 4 experiments, rats were given intermixed or blocked preexposure to an array of landmarks that subsequently defined the location of a hidden goal in a Morris pool task. Previous research has shown that intermixed preexposure to pairs of adjacent landmarks retards learning whereas preexposure to individual landmarks facilitates subsequent learning (J. Prados, V. D. Chamizo, & N. J. Mackintosh, 1999). Accordingly, in Experiment 1, intermixed and blocked preexposure to pairs of adjacent landmarks was found to retard learning. In Experiment 2, however, a scheduling effect was found: Rats given intermixed preexposure to the individual landmarks learned faster than rats given blocked or no preexposure. Experiment 3 showed that intermixed (but not blocked) preexposure to pairs of landmarks resulted in a facilitatory effect when preexposure and test were carried out in different contexts. Experiment 4 replicated within a single experiment the main results observed in Experiments 1 and 3. This pattern of results suggests that intermixed preexposure engages learning processes other than latent inhibition that facilitate subsequent learning of the navigation task.     

Thinking outside of the box: Transfer of shape-based reorientation across the boundary of an arena

The way in which human and non-human animals represent the shape of their environments remains a contentious issue. According to local theories of shape learning, organisms encode the local geometric features of the environment that signal a goal location. In contrast, global theories of shape learning suggest that organisms encode the overall shape of the environment. There is, however, a surprising lack of evidence to support this latter claim, despite the fact that common behaviours seem to require encoding of the global-shape of an environment. We tested one such behaviour in 5 experiments, in which human participants were trained to navigate to a hidden goal on one side of a virtual arena (e.g. the inside) before being required to find the same point on the alternative side (e.g. the outside). Participants navigated to the appropriate goal location, both when inside and outside the virtual arena, but only when the shape of the arena remained the same between training and test (Experiments 1a and 1b). When the arena shape was transformed between these stages, participants were lost (Experiments 2a and 2b). When training and testing was conducted on the outside of two different-shaped arenas that shared local geometric cues participants once again explored the appropriate goal location (Experiment 3). These results provide core evidence that humans encode a global representation of the overall shape of the environments in, or around, which they navigate.     

Failure of a landmark to restrict spatial learning based on the shape of the environment

Rats were required to find a submerged platform in the corner of a swimming pool with a distinctive shape. A landmark near the platform did not interfere with the control acquired by the pool's shape over searching for the platform. This outcome was observed with an overshadowing and a blocking design. A comparison of the ease with which the landmark and the pool's shape gained control over searching for the platform indicates that the failure of overshadowing and blocking was not a consequence of the landmark being less salient than the shape of the pool. The results are not readily explained by theories of associative learning, but they are consistent with the claim that learning about the shape of the environment takes place in a dedicated module, which excludes information about the significance of individual landmarks.     

In search of a strong visual recency effect

When a sequence of visual stimuli is presented in a fixed location, immediate serial recall of the sequence is characterized by only a small recency effect. According to Battacchi, Pelamatti, and Umiltà (1990), the distribution of visual stimuli over space, as well as time, greatly enhances the recency effect. After an initial failure to find a strong visual recency effect with distributed presentation (Experiment 1), in the remaining experiments an attempt was made to more closely approximate Battacchi et al.'s methodology by eliminating articulatory suppression (Experiments 2-7), using their stimuli (Experiments 3-7), blocking conditions (Experiments 4-7), requiring written rather than typed responses (Experiments 5-7), and using their list length (Experiments 6 and 7). Nevertheless, even when their method was followed as closely as possible (Experiment 7), distributed presentation did not produce a strong visual recency effect. The influence of distributed presentation on the visual recency effect would seem to be, at best, limited.     

On the role of knowledge of results in motor learning: exploring the guidance hypothesis

Recent work on the role of knowledge of results (KR) in motor learning has challenged some traditional assumptions. In particular, the guidance hypothesis suggests that there is a detriment to learning when KR guides the learner toward correct performance. Three experiments that explored this hypothesis are reported here. These experiments contrasted the effects of relative frequency of guidance versus the relative frequency of KR. According to the guidance hypothesis, it was predicted that parallel effects of the relative frequency manipulation on motor learning and performance would result under guided and KR conditions. The movement task was a reciprocal timing task that was either paced by a metronome (Experiment 1) or augmented by auditory KR (Experiments 2 and 3). The results of Experiments 1 and 3 revealed a number of parallel effects, thus providing support for the guidance hypothesis. The contrast of Experiments 1 and 2 resulted in a number of dissociable effects, however. These findings are discussed in relation to the potential guiding properties of KR and their impact on motor performance and learning.     

Implicit chaining in cotton-top tamarins (Saguinus oedipus) with elements equated for probability of reinforcement

Three experiments examined the implicit learning of sequences under conditions in which the elements comprising a sequence were equated in terms of reinforcement probability. In Experiment 1 cotton-top tamarins (Saguinus oedipus) experienced a five-element sequence displayed serially on a touch screen in which reinforcement probability was equated across elements at .16 per element. Tamarins demonstrated learning of this sequence with higher latencies during a random test as compared to baseline sequence training. In Experiments 2 and 3, manipulations of the procedure used in the first experiment were undertaken to rule out a confound owing to the fact that the elements in Experiment 1 bore different temporal relations to the intertrial interval (ITI), an inhibitory period. The results of Experiments 2 and 3 indicated that the implicit learning observed in Experiment 1 was not due to temporal proximity between some elements and the inhibitory ITI. The results taken together support two conclusion: First that tamarins engaged in sequence learning whether or not there was contingent reinforcement for learning the sequence, and second that this learning was not due to subtle differences in associative strength between the elements of the sequence.