The primary intent of this study was to gain insight into the developmental nature of spatial perception and representation. More specifically, the work presented here examined 1) the age-related ability to modulate peri- and extrapersonal space via hand and tool use, 2) the adjustment period associated with extending and retracting spaces, and 3) the effect of tool length on modulation of space. Seventy children representing age groups 7-, 9-, 11 years and adults were presented with two experiments using an estimation of reach paradigm involving hand and tool conditions and a switch-block of the opposite condition. Experiment 1 tested Hand and Tool (20cm length) estimation and found a significant effect for Age, Space, and an Age x Space interaction (ps <.05). Both children and adults were less accurate in extrapersonal space, indicating an overestimation bias. Interestingly, the adjustment period during the switch-block condition was immediate and similar across age. Experiment 2 was similar to Experiment 1 with the exception of using a 40cm length tool. Results of 55 participants also revealed a difference in estimation responses between Age groups (p <.05); 7- and 9-year-olds were similar and less accurate than adults, and 11-year-olds were not different from any other age group. There was also a difference in Space (p <.05), revealing that participants underestimated their reaching abilities with higher accuracy in extrapersonal space. Interestingly, whereas participants overall overestimated with the 20cm tool, they tended to underestimate while using the 40cm tool. This finding suggests that participants were less confident when presented with a longer tool, even though the adjustment period with both tool lengths was similar. Considered together, these results hint that: (1) children as young as 6 years of age are capable of re-scaling peripersonal space via tool use in the context of estimation reach, (2) the adjustment period associated with extending and retracting spaces is immediate rather than gradual, and (3) tool length may influence confidence of participants, shifting the general direction of error from overestimation with a 20cm tool to underestimation with a 40cm tool.

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<p>Based on evidence from studies involving animal single cell recording, animal brain lesion, and human brain damage, researchers have suggested that there may be differential visual representations for objects in near (peripersonal, within arm’s reach) and far (extrapersonal, beyond arm’s reach) space in the human visual system. The findings in Chapter 2 and Chapter 3 of the present thesis provide the first behavioural evidence suggesting that healthy human observers prefer to rely on different visual mechanisms in processing information in near and far spaces. The different performance in detecting visual targets presented in near and far space indicates that the brain can actively modulate the information processing either in parvocellular and magnocellular pathways or in ventral and dorsal streams. <br /> To determine the loci of the neural modulation regarding near and far viewing, visual identification tasks were employed in Chapter 4. In four experiments, visual stimuli were presented in either isoluminant green or achromatic white in order to decouple the neural processing in parvocellular and magnocellular pathways. The different patterns of the visual performance in the four experiments suggest that the change to near or far viewing distance results in altered information transmission in parvocellular and magnocellular pathways. Thus, the data in the present thesis provide the first behavioural evidence indicating that the LGN serves as a gatekeeper for regulating and redistributing visual information for later cortical analysis.</p> / Doctor of Science (PhD)