Human Visual Navigation: Effects of Visual Context, Navigation Mode, and Gender

Abstract This thesis extends research on human visual path integration using optic flow cues. In three experiments, a large-scale path-completion task was contextualised within highly-textured authentic virtual environments. Real-world navigational experience was further simulated, through the inclusion of a large roundabout on the route. Three semi-surrounding screens provided a wide field of view. Participants were able to perform the task, but directional estimates showed characteristic errors, which can be explained with a model of distance misperception on the outbound roads of the route. Display and route layout parameters had very strong effects on performance. Gender and navigation mode were also influential. Participants consistently underestimated the final turn angle when simulated self-motion was viewed passively, on large projection screens in a driving simulator. Error increased with increasing size of the internal angle, on route layouts based on equilateral or isosceles triangles. A compressed range of responses was found. Higher overall accuracy was observed when a display with smaller desktop computer monitors was used; especially when simulated self-motion was actively controlled with a steering wheel and foot pedals, rather than viewed passively. Patterns and levels of error depended on route layout, which included triangles with non-equivalent lengths of the two outbound roads. A powerful effect on performance was exerted by the length of the "approach segment" on the route: that is, the distance travelled on the first outbound road, combined with the distance travelled between the two outbound roads on the roundabout curve. The final turn angle was generally overestimated on routes with a long approach segment (those with a long first road and a 60° or 90° internal angle), and underestimated on routes with a short approach segment (those with a short first road or the 120° internal angle). Accuracy was higher for active participants on routes with longer approach segments and on 90° angle trials, and for passive participants on routes with shorter approach segments and on 120° angle trials. Active participants treated all internal angles as 90° angles. Participants performed with lower overall accuracy when optic flow information was disrupted, through the intermittent presentation of self-motion on the small-screen display, in a sequence of static snapshots of the route. Performance was particularly impaired on routes with a long approach segment, but quite accurate on those with a short approach segment. Consistent overestimation of the final angle was observed, and error decreased with increasing size of the internal angle. Participants treated all internal angles as 120° angles. The level of available visual information did not greatly affect estimates, in general. The degree of curvature on the roundabout mainly influenced estimates by female participants in the Passive condition. Compared with males, females performed less accurately in the driving simulator, and with reduced optic flow cues; but more accurately with the small-screen display on layouts with a short approach segment, and when they had active control of the self-motion. The virtual environments evoked a sense of presence, but this had no effect on task performance, in general. The environments could be used for training navigational skills where high precision is not required

Age-related changes in memory for object locations across different perspectives.

One important aspect of spatial cognition is the ability to recognize and remember spatial locations across different viewpoints. Previous research has suggested that those abilities decline in older adults. The aim of the current PhD project is to develop a clearer understanding of what may be contributing to age-related declines in recognising object locations from different perspectives. Specifically, focusing on how ageing effects encoding strategies that are used to memorize spatial configurations and the precision with which object/landmark locations are remembered. In Chapter 2, gaze behaviour was recorded during a task in which young and older adults judged whether previously encoded objects have remained in the same position or were displaced following perspective shifts. Ageing was associated with declines in spatial processing abilities. Additionally, older adults displayed a more conservative decision style and relied more on encoding object positions using room-based cues compared to young adults, who focused on the spatial relations among the to-be remembered objects during encoding. In Chapter 3, age-related differences in encoding strategies were further investigated using a modified version of the task used in Chapter 2 in which the availability and utility of the room- based cues was manipulated. Performance accuracy was similar across both age groups, yet, older adults displayed a greater preference towards a more categorical encoding strategy in which they formed spatial relations between objects and room-based cues. In the remaining chapters the focus shifted to investigating the precision with which object locations are remembered across different perspectives. In Chapter 4 participants memorized the position of an object in a virtual room and then judged from a different perspective, whether the object has moved to the left or to the right. Results revealed that participants exhibited a systematic bias in their responses that was termed the reversed congruency effect. Specifically, participants performed worse when the camera and the object moved in the same direction than when they moved in opposite directions. In Experiment 2, it was shown that the presence of additional objects in the environment reduced the reversed congruency effect whilst in Experiment 3 the reversed congruency effect was greater in older adults, suggesting that the quality of spatial memory and perspective-taking abilities are critical in mediating the reversed congruency effect. In Chapter 5, a novel task was used to investigate the systematic bias reported in Chapter 4. In this task participants encoded the position of an object in a virtual room and then estimated the object’s position following a perspective shift. In addition, memory load was manipulated. Overall, participants systematically overestimated the position of the object in the direction of the perspective shift. This bias was present in both memory and perception conditions. In Chapter 6, these results were replicated in an online-based version of the study. Lastly in Chapter 7, the influence of camera translations and camera rotations on the perspective shift related bias was decoupled. Additionally, the study investigated whether adding more information into the scene would reduce the bias and if there are age-related differences in the precision of object location estimates and the tendency to display the bias related to perspective shift. Overall, camera translations led to a greater systematic bias than camera rotations. Furthermore, the use of additional spatial information improved the precision with which object locations were estimated and reduced the bias associated with camera translation. Finally, although older adults were as precise as younger participants when estimating object locations, they benefited less from additional spatial information and their responses were more biased in the direction of camera translations. Overall, by combining eye-tracking and diffusion modelling the current thesis shows that ageing is associated with changes in the type of information that is used to encode object locations across different perspectives. Additionally, ageing was found to be particularly associated with impairments in the formation of fine-grained spatial representations. Furthermore, a novel bias in spatial memory across different perspectives has been identified. It is proposed that the perspective shift related bias is driven by uncertainty about object position following a perspective shift that leads participants to rely on an egocentric anchor when estimating the location of an object

Using Realistic Virtual Environments in the Study of Spatial Encoding

Computer generated virtual environments have reached a level of sophistication and ease of production that they are readily available for use in the average psychology laboratory. The potential benefits include cue control, incorporation of interactivity and novelty of environments used. The draw-backs include limitations in realism and lack of fidelity. In this chapter we describe our use of virtual environments to study how 3D space is encoded in humans with special emphasis on realism and interactivity. We describe the computational methods used to implement this realism and give examples from studies concerning spatial memory for object form, spatial layout and scene recognition