The primary intent of this study was to gain insight into children's ability to use visual information in planning reaching movements. More specifically, the work presented here examined, from a developmental perspective, the use of visual information to use a) egocentric cues, b) allocentric cues, and c) the combination, in the form of visual background around a target. Children representing the age groups 5-, 7-, 9-, 11 years and adults participated in three experiments. All experiments were conducted using an immediate (visually-guided) and response-delay (memory-guided) paradigm. Experiment 1 examined the ability of participants to use an egocentric frame of reference to estimate reach via motor imagery. Results indicated that introducing a >̲ 2s delay affected responses in all age groups, especially the younger age groups (5- and 7-year-olds). As delay increased, children as a group tended to overestimate, while adults underestimated. Experiment 2 investigated how participants used allocentric cues to estimate the location of objects in a perceptual estimate paradigm. Results revealed that introducing a delay affected the estimation of distance among all age groups, with greater effect on the younger age groups. Experiment 3 examined how a visual background surrounding a target would affect estimation of reach. Results revealed that there were no differences when targets were surrounded with or without a background. Results also showed that the 5- and 7-year-olds were most affected on their perception of reach and estimates by longer delays. Considered together, these results hint that: (1) there is a significant temporal constraint on the representation of movement through the visoumotor stream, especially with children 7 years and younger, and (2) children as a whole tend to operate and rely more on an egocentric frame of reference; therefore, responses of reachability and distance estimates were susceptible to greater error when performed after a 2s delay.

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In the study of navigation, frequently it is assumed that navigation is accomplished using either an allocentric strategy based on a cognitive map, or an egocentric strategy based on stimulus response associations. Further, it is frequently assumed that individual navigators, or even entire genders, are only capable of navigating by one strategy or the other. The present study investigated whether individuals or genders were limited to a particular navigational strategy and whether both strategies might be learned or used at the same time. In the present study, undergraduate students were tested in a virtual Morris water maze that was modified to allow successful and efficient navigation using either an allocentric or an egocentric strategy. Learning trials on which the participants had to learn the location of the platform were alternated with probe trials on which participants would show which strategy they were using. At the end of testing, participants were given a series of tests to determine what knowledge they had acquired and which strategies they were capable of using. Results indicated that: a) most people preferred to navigate egocentrically in this maze, but some preferred to navigate allocentrically, b) people tended to use an egocentrically strategy first, but it was not a necessary step to learning to navigate allocentrically, c) people were better at their preferred strategy, d) people learned information about their non-preferred strategy, and e) those who preferred to navigate egocentrically could nevertheless learn to navigate allocentrically. Surprisingly, all of these results were true for both men and women, although women tended to prefer egocentric navigation at a higher rate than men, and men outperformed women when forced to navigate allocentrically. These results suggest it may be too simple to think of navigators as being capable of only a single navigational strategy or of learning only one strategy at a time. / Graduate

In this thesis, I study the computational advantages of the allocentric represen- tation as compared to the egocentric representation for autonomous local navigation. Whereas in the allocentric framework, all variables of interest are represented with respect to a coordinate frame attached to an object in the scene, in the egocentric one, they are always represented with respect to the robot frame at each time step. In contrast with well-known results in the Simultaneous Localization and Mapping literature, I show that the amounts of nonlinearity of these two representations, where poses are elements of Lie-group manifolds, do not affect the accuracy of Gaussian- based filtering methods for perception at both the feature level and the object level. Furthermore, although these two representations are equivalent at the object level, the allocentric filtering framework is better than the egocentric one at the feature level due to its advantages in the marginalization process. Moreover, I show that the object- centric perspective, inspired by the allocentric representation, enables novel linear- time filtering algorithms, which significantly outperform state-of-the-art feature-based filtering methods with a small trade-off in accuracy due to a low-rank approximation. Finally, I show that the allocentric representation is also better than the egocentric representation in Model Predictive Control for local trajectory planning and obstacle avoidance tasks.

Considerable research has examined strategies involved in spatial navigation, and what factors determine which strategy an individual will use. The little research that has examined strategy adoption has produced conflicting results. The present study investigated the relative rate of adoption of allocentric and egocentric strategies in an environment that allowed individuals to adopt one or the other, or switch between them. Results indicated that by the end of testing nearly all participants had adopted one strategy or the other. Also, more participants were using an allocentric strategy than an egocentric strategy. However, strategy selection was not related to gender, or the relative efficiency of the two strategies. Analysis of gaze position at the start of trials showed that those who adopted an allocentric strategy tended to focus their attention on the distal (landscape) features of the environment whereas those who adopted an egocentric strategy tended to focus their attention on the proximal object features. However, vertical gaze position could not be used to reveal the rate of adoption of an egocentric strategy, because this did not vary over trials. Analysis of gaze position using “regions of interest” overcame this problem and showed that both strategies are adopted at a similar rate early in trials. Comparison of strategy by gaze position and strategy by navigation probe indicated that these two metrics were measuring two different stages of navigation. Finally, analysis of the navigational efficiency of different strategies indicated that the best navigators were those who used both strategies. These findings indicate allocentric and egocentric strategies are adopted at a similar rate and that within the space of a few seconds, individuals may use different strategies for orientation and navigation. / Graduate

The research program described in this dissertation updates the knowledge base concerning human navigation and presents new methods for investigating selection and use of cognitive navigational strategies. Four experiments were designed to answer questions about the effects of environmental and experiential factors on cognitive mapping and selection of navigation strategies. Humans are thought to navigate using two different reference frames often referred to as “world based” and “person based”. These reference frames correspond to two probable cognitive/memory systems respectively labelled “allocentric” for the formation and use of cognitive maps of the environment, and “egocentric” for navigation by stimulus response or guidance. Different navigational strategies are associated with the two systems. Allocentric strategies rely on the presence of a stable environmental structure containing a number of more distal, relational stimuli whereas egocentric strategies rely only on the presence of simple, local cues (cue-based egocentric) or on body movements (response-based egocentric). The experiments tested navigation behaviour and strategy selection using virtual environment analogues of an animal model, the Morris water maze. Adaptations included, 1) the Place maze biasing participants toward the use of an allocentric strategy, 2) the Cue maze (and Floor Cue maze) biasing participants toward the use of an egocentric strategy, and 3) the Dual-strategy maze that has no bias because participants can choose to utilize either an allocentric or egocentric strategy. Experiment 1 was a behavioural study testing 101 university students in the Place maze and Floor Cue maze, with and without the opportunity to explore the environment before testing. The experiment showed for the first time that exploration is necessary for allocentric but not for egocentric navigation, suggesting that prior exploration is important for cognitive mapping. Experiment 2 outlined a novel and reliable eye tracking method for differentiating strategy use in the Place and Cue mazes. Eye movements were measured during the first orientation second of behavioural trials to differentiate allocentric from egocentric strategy use. Experiment 3 employed the established eye tracking method to test the effects of experience on strategy selection. Participants were trained in either the Place maze or the Cue maze and then tested in the Dual-strategy maze. A strategy probe trial was introduced at the end of testing to indicate whether participants had selected an allocentric or an egocentric strategy. Training experience had a strong behavioural effect on later strategy selection at the end of testing. Furthermore the effect of experience occurred independently of the gender of participants. However, the experience effect was only briefly shown using eye tracking measures. Experiment 4 was a successful feasibility study showing that eye tracking measures can be utilized to measure navigational strategy use in survivors of traumatic brain injury. Together these experiments may indicate that strategies are not innate or within the person but rather are interactions of the person with the environment. / Graduate

Cognitive processes associated with spatial orientation can use different reference frames: egocentric, centered on observer and allocentric, centered on objects in the environment. In this thesis, we use EEG to investigate the dynamics of brain processes accompanying spatial orientation based on these reference frames. Participants were instructed to estimate distances between objects or themselves and objects located in a virtual circular arena; this task was presented in both 2D and 3D displays. Task-related EEG changes were analyzed using a time-frequency analysis and event-related potential analysis of 128-channel EEG recordings. Through time-frequency analysis we found significant power differences in delta, theta, alpha, beta and gamma bands amongst the control, egocentric and allocentric testing conditions. We noted a decrease in alpha power in occipital and parietal regions, while a significantly stronger decrease was observed for the allocentric condition compared to both egocentric and control conditions. A similar pattern was also detectable for the beta band. We also report an increase in theta and delta power in temporal, fronto-temporal and lateral frontal regions that was significantly stronger for the egocentric condition compared to control and, in some electrodes, even...

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<p>Previous human behavioral research has provided support for the existence of different frames of reference utilized during spatial processing that can be dependent or independent of the observer. These are known respectively as egocentric and allocentric frames of reference. However, it has been difficult to dissociate these two different processes under realistic conditions. Importantly, how these frames of reference are influenced by the visual and non-visual information is not well understood. Therefore, the studies of this thesis evaluated spatial processing utilizing realistic and ecologically valid stimuli in environments of different scales, while systematically manipulating the visual and non-visual information available during learning. We demonstrated that non-visual information generated by actively walking through an environment leads to more egocentric processing, whereas the same visual motion information presented passively via a video leads to more allocentric processing (Chapter 2). Further, characteristics of the visual scene can also influence how it is processed, dependent on the strength of the verbal identity of the features in the environment (Chapter 3). Specifically, in a small room environment subject’s representations of corners-to-corners (corners do not have an obvious verbal component) were not as strongly encoded relative to each other in comparison to objects-to-objects (objects with an obvious verbal identity ). Finally, we demonstrated differential influences of non-visual information dependent on whether the features in the visual scene were more allocentrically processed or egocentrically processed (Chapter Four). Specifically, when different features of layouts are made distinguishable by their identity, this lead to more allocentric processing whereas when different features are made distinguishable by their relative position, this lead to more egocentric processing. Further, non-visual information made available during spatial updating when the observer is changing viewpoints benefitted tasks focused on differentiating changes to objects’ identity and less so for differentiating changes in relative object position.</p> / Doctor of Philosophy (PhD)

Episodic memory is processed by the extended hippocampal system, and pathology or injury to individual components of this system can result in deficits in spatial learning and memory (Aggleton & Brown, 1999). Extensive research regarding spatial memory has been carried out on the anterior thalamic nuclei, a component of the extended hippocampal system, but the contribution of the laterodorsal thalamic nuclei, an adjacent structure with similar neural connections, is less clear. The purpose of the present study was to compare the effects of selective anterior thalamic nuclei lesions (AT) with selective laterodorsal thalamic nuclei lesions (LD) in a novel land-based spatial reference memory task. This assessed the use of proximal and distal visual cues on the propensity to use allocentric or egocentric navigation strategies to locate a specific place in space, as well as the temporal evolution of these navigation strategies. AT lesion impairments were observed in the acquisition trials in both proximal and distal cue conditions. LD lesion rats were unimpaired in the acquisition trials in both visual cue conditions. Across the probe trials, lesion effects were not observed when tested for general navigation, egocentric or allocentric strategies, and there was no clear improvement in performance over the four weeks of probe trials. However, performance was consistently poorer for all groups when proximal cues facilitated navigation compared to distal cues. Performance differences related to cue proximity may reflect the influence of motion parallax, the perceived displacement rate of visual cues. The absence of lesion effects across probes were thought to be due to the preferential use of cued navigation, which was reliant on a single salient beacon, and the lack of integration between cued and place navigation, which was reliant on the formation of a spatial representation.