Do not ask whether they have a cognitive map, but how they find their way about.

find their way abou

Cue competition between shapes in human spatial learning

In many species, including humans the basic ability to move to a goal is essential to survival. Central to understanding how this ability operates in the cognitive systems of humans and other animals is whether learning about spatial relationships follows the same principles as learning about other kinds of contingent relationships between events. In non-spatial contingent relationships, learning about one stimulus can influence learning about other stimuli. For example, in blocking, learning that cue-A predicts an outcome can reduce learning about a subsequently added cue-B that is paired with cue-A when both cues predict the same outcome (Kamin, 1969). To the extent that spatial learning operates according to similar principles to other forms of contingency learning, spatial cues that can be used to locate a goal should also compete with each other. Failure to find blocking between spatial cues that can be used to locate a goal would be consistent with an alternative account of how spatial knowledge is acquired and used: one that assumes a quite different learning mechanism. For example, the hypothesis of locale learning assumes that a cognitive map of the environmental layout is automatically updated when cues are added or removed from the environment (O'Keefe and Nadel, 1978). Automatic updating implies that added or removed cues will be processed irrespective of what is learned about other cues, rather than competing with or otherwise interacting with those other cues. A second, related, hypothesis is that the geometric properties of the environment are processed in an independent module that is impervious to cue competition from non-geometric features (Cheng, 1986; Gallistel, 1990). This hypothesis implies that geometric cues within the module are also immune to competition from each other. In the current experiments, evidence for blocking of goal location learning was investigated in virtual environments (VEs) in which the presence or absence of large-scale structures can be manipulated. Experiment 1 found that an irregular-shaped flat-walled enclosure blocked learning about a landmark subsequently placed within its boundaries, providing preliminary evidence that shape may not be processed in a specialised module. However, many participants appeared not to be using shape to locate the goal. In the remaining experiments, spatial cues were large-scale 2D shapes presented on the ground which ensured that participants perceived overall shape. Experiments 2 and 3 found no evidence of blocking between shapes when these stimuli were presented in the context of minimal "auxiliary" cues. When additional auxiliary stimuli were presented throughout learning in Experiment 4, a direction consistent with blocking was found, but the effect was not statistically significant. In Experiments 5 and 6 a clear blocking effect was found under circumstances that suggested that the critical variable to finding blocking was the number of irrelevant shapes present either during training or at test. Experiment 7 confirmed that, rather than the test conditions, the presence or absence of stimuli during one or both training phases was the crucial variable in promoting blocking. Experiment 8 investigated the hypothesis that an initial process of learning to ignore irrelevant shapes in phase 1 is a requirement for blocking of learning. In the absence of auxiliary cues in phase 1, blocking was not found. The implications of these outcomes are discussed in relation to the hypothesis of specialised geometric processing, changes in attention, and the conditions of discrimination learning

Cue competition between shapes in human spatial learning

In many species, including humans the basic ability to move to a goal is essential to survival. Central to understanding how this ability operates in the cognitive systems of humans and other animals is whether learning about spatial relationships follows the same principles as learning about other kinds of contingent relationships between events. In non-spatial contingent relationships, learning about one stimulus can influence learning about other stimuli. For example, in blocking, learning that cue-A predicts an outcome can reduce learning about a subsequently added cue-B that is paired with cue-A when both cues predict the same outcome (Kamin, 1969). To the extent that spatial learning operates according to similar principles to other forms of contingency learning, spatial cues that can be used to locate a goal should also compete with each other. Failure to find blocking between spatial cues that can be used to locate a goal would be consistent with an alternative account of how spatial knowledge is acquired and used: one that assumes a quite different learning mechanism. For example, the hypothesis of locale learning assumes that a cognitive map of the environmental layout is automatically updated when cues are added or removed from the environment (O'Keefe and Nadel, 1978). Automatic updating implies that added or removed cues will be processed irrespective of what is learned about other cues, rather than competing with or otherwise interacting with those other cues. A second, related, hypothesis is that the geometric properties of the environment are processed in an independent module that is impervious to cue competition from non-geometric features (Cheng, 1986; Gallistel, 1990). This hypothesis implies that geometric cues within the module are also immune to competition from each other. In the current experiments, evidence for blocking of goal location learning was investigated in virtual environments (VEs) in which the presence or absence of large-scale structures can be manipulated. Experiment 1 found that an irregular-shaped flat-walled enclosure blocked learning about a landmark subsequently placed within its boundaries, providing preliminary evidence that shape may not be processed in a specialised module. However, many participants appeared not to be using shape to locate the goal. In the remaining experiments, spatial cues were large-scale 2D shapes presented on the ground which ensured that participants perceived overall shape. Experiments 2 and 3 found no evidence of blocking between shapes when these stimuli were presented in the context of minimal "auxiliary" cues. When additional auxiliary stimuli were presented throughout learning in Experiment 4, a direction consistent with blocking was found, but the effect was not statistically significant. In Experiments 5 and 6 a clear blocking effect was found under circumstances that suggested that the critical variable to finding blocking was the number of irrelevant shapes present either during training or at test. Experiment 7 confirmed that, rather than the test conditions, the presence or absence of stimuli during one or both training phases was the crucial variable in promoting blocking. Experiment 8 investigated the hypothesis that an initial process of learning to ignore irrelevant shapes in phase 1 is a requirement for blocking of learning. In the absence of auxiliary cues in phase 1, blocking was not found. The implications of these outcomes are discussed in relation to the hypothesis of specialised geometric processing, changes in attention, and the conditions of discrimination learning

Components of Spatial Learning in the Rat

A series of experiments were conducted to investigate the nature of how navigational systems interact in the rat (Rattus norvegicus) and the neural structures that support these interactions. The first set of experiments focused on geometry learning and how a reference frame based on the shape of the environment interacted with other non-geometric reference frames. The results revealed that rats were capable of rapidly integrating geometric cues with featural cues in only a single exposure to the cues in compound. This is a novel contribution to the current literature as it opposes the notion that featural information can only be ‘pasted on’ to a geometric reference frame over time. The effect of the rats’ sex on their propensity to use geometric and landmark cues was also investigated. The findings are the first to reveal no difference between male and female rats in the extent to which landmarks overshadow geometry learning when generalization decrement is controlled for. However, in a separate task, male rats were able to use both relevant geometric and landmark information better than female rats following changes to the relative reliability of environmental cues. In a separate series of experiments, the navigational strategies rats rely upon and the neural substrates underpinning these strategies was investigated. In a task requiring rats to use the colours of the enclosure walls to locate a hidden goal, it was found that the performance of rats with hippocampal damage and rats with dorsolateral striatum damage was identical to that of normal rats, i.e. they all solved the task using an allocentric strategy over an egocentric strategy. Importantly, the findings revealed that the hippocampus is not required to learn the spatial relationship between differently coloured features. A separate task revealed that hippocampal damage enhanced landmark learning (egocentric), and dorsolateral striatum damage enhanced room cue learning (allocentric) suggesting that these two systems compete for behavioural control in normal rats. Finally, the last experiment revealed that, under certain training conditions, the hippocampus is not critical for the acquisition of a place solution but is more likely involved in a path integration process. This result holds important implications for the role of the hippocampus in ‘knowing where’ versus ‘getting there’

An analysis of within-compound associations in spatial learning

The nature of spatial learning has been argued to be qualitatively different from that of associative learning. Compelling evidence for this argument is provided by experiments showing a lack of typical associative cue competition between spatial and non-spatial cues. However, this lack of cue-competition is also evident in wholly nonspatial experiments and has been explained by the presence of within-compound associations: an associative phenomenon. This thesis aims to determine whether such associations can explain similar cue-competition failures in spatial learning. In a series of experiments it is shown that these within-compound associations exist between spatial and non-spatial cues in the rat, and that they can account for the frequent failure to observe typical cue-competition between these cues. In addition, it is demonstrated that the extent to which this failure occurs depends upon the relative salience of the cues in question. In related experiments, it is also shown that these within-compound associations between spatial and non-spatial cues exist in humans. However, manifestation of these associations appears to depend on the gender of the participant, with associations forming in males but not in females. Further experiments suggest that this difference is likely due to the fact that the females are much less able to learn about the spatial cues in question. It is argued that spatial learning need not be qualitatively different from associative learning if such associative phenomena as within-compound associations are accounted for

An Examination of Hippocampal and Prefrontal Contributions to Spatial Learning and Memory using Immediate Early Gene Imaging

The hippocampus and medial prefrontal cortex are two brain regions which have repeatedly been linked to spatial learning and memory processing; however, the precise roles of individual sub-regions within these areas continue to be debated. The Morris water maze is a well-known behavioural task used to measure spatial memory. Despite its popularity, the type of spatial information animals encode and ultimately rely on for accurate navigation in this task remains unclear. Therefore, the primary objectives of this thesis were to conduct an in-depth investigation into the use of navigation strategies during memory encoding and retrieval in the water maze, and to characterise the specific contributions of the hippocampus and medial prefrontal cortex to these processes using Immediate Early Genes (IEG) imaging. In addition, we investigated the mechanisms underlying neuronal activation by inhibiting ionotropic glutamate receptors (NMDA and AMPA) during or after spatial learning. We found novel evidence that the salience (or noticeability) of environmental cues significantly impacted the type of learning strategy used (i.e. simple or complex), and that increased training led to more flexible responding (i.e. strategy switching). We also discovered that NMDA receptor-mediated activation in area CA1 (indexed by Zif268) was tightly linked to learning-related plasticity, and activation in CA3, prelimbic and anterior cingulate cortices was strongly associated with flexible spatial memory recall (i.e. pattern completion). Finally, we revealed that spatial memory deficits induced by NMDA receptor blockade could be partially prevented by extended environmental experience

The well-worn route revisited: Striatal and hippocampal system contributions to route learning in human navigation

Parallel spatial memory systems theory posits that there are two types of memory system. One is a flexible, cognitive mapping system subserved by the hippocampal formation, and the other is a system centred on the striatum based on reinforcement learning principles where specific stimuli are associated with rewarded actions (O’Keefe & Nadel, 1978; White & McDonald, 2002). More recently, Khamassi & Humphries (2012) have argued that the division between model-based and model-free spatial learning is a better predictor of whether hippocampal or striatal systems will be recruited, with hippocampal systems associated with model-based responding and striatal systems with model-free responding. Model-free decision-making occurs when responding is based on average reward history associated with a particular cue-action pairing, whereas model-based decision-making allows knowledge of outcomes from previous learning history to be represented. We sought to test these theories by asking participants (N = 24) to navigate within a virtual environment through a previously learned, 9-junction route with distinctive landmarks at each junction, while undergoing functional magnetic resonance imaging. In critical conflict probe trials, a landmark was presented out of sequence such that following the usual sequence of actions would generate an opposite response to following the learned individual landmark-action association, now out of sequence. Participants that made sequence-based responses had higher parahippocampal activations relative to participants that made responses based on the individual landmark-action association, a result that would be predicted by the need to recruit model-based systems to make a sequence-based response. Parallel spatial memory systems theory would not predict hippocampal formation recruitment for either response in the conflict probe, because no cognitive mapping is required when following a prescribed route. In longer probe trials where participants were able to plan a sequence of responses, striatal systems were recruited (caudate and putamen) suggesting a role for striatum in action chunking

Associative analysis of spatial learning in environments with a distinctive shape

The aim of this thesis was to evaluate the proposal by Miller and Shettleworth (2007) that learning about geometric cues in environments with a distinctive shape is governed by a competitive learning rule (e.g., Rescorla & Wagner, 1972). To do this, in all experiments, rats were trained to locate a hidden platform by reference to the shape of a swimming pool. Chapter 2 (Experiments 1 -4) assessed whether a landmark suspended above the platform would overshadow learning about geometric cues. No overshadowing was recorded, even when the salience of the geometric cues was reduced. These findings are inconsistent with the model of Miller and Shettleworth (2007). In Chapter 3 (Experiments 5-7), a blocking paradigm was used. When rats were given extended pre-training with a landmark above the platform, only then did the landmark successfully block learning about geometric cues. However, some unexpected findings suggested that perhaps the spatial cues were competing for attention rather than associative strength. The experiments in Chapter 4 (Experiments 8 and 9) successfully demonstrated superconditioning of geometric cues by an inhibitory landmark providing convincing evidence that learning about geometric cues is governed by the principles of associative learning. Miller and ShettlewortiVs (2007) model however, failed to predict this outcome. Experiments 10-13 in Chapters 5 and 6 showed that associations formed between geometric and non-geometric cues. This outcome provides the basis for a viable explanation for potentiation and for the past failures to find cue competition in the spatial domain. The empirical findings of this thesis show that learning about geometric cues is not entirely void of associative processes as once thought. A number of recent models of spatial learning are discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Dissociable contributions of the prefrontal cortex to hippocampus- and caudate nucleus-dependent virtual navigation strategies

AbstractThe hippocampus and the caudate nucleus are critical to spatial– and stimulus–response-based navigation strategies, respectively. The hippocampus and caudate nucleus are also known to be anatomically connected to various areas of the prefrontal cortex. However, little is known about the involvement of the prefrontal cortex in these processes. In the current study, we sought to identify the prefrontal areas involved in spatial and response learning. We used functional magnetic resonance imaging (fMRI) and voxel-based morphometry to compare the neural activity and grey matter density of spatial and response strategy users. Twenty-three healthy young adults were scanned in a 1.5T MRI scanner while they engaged in the Concurrent Spatial Discrimination Learning Task, a virtual navigation task in which either a spatial or response strategy can be used. In addition to increased BOLD activity in the hippocampus, spatial strategy users showed increased BOLD activity and grey matter density in the ventral area of the medial prefrontal cortex, especially in the orbitofrontal cortex. On the other hand, response strategy users exhibited increased BOLD activity and grey matter density in the dorsal area of the medial prefrontal cortex. Given the prefrontal cortex’s role in reward-guided decision-making, we discuss the possibility that the ventromedial prefrontal cortex, including the orbitofrontal cortex, supports spatial learning by encoding stimulus-reward associations, while the dorsomedial prefrontal cortex supports response learning by encoding action-reward associations