The Study Of Visual Perception Of Distance Based On Intrinsic Bias

To survive in the world, one has to accurately judge the egocentric distance between the target and oneself. In the bright natural environment with full cue, humans can judge egocentric distance with considerable accuracy (less than 30 meters). Both external depth cues and or internal knowledge are used by the visual system to construct the visual perceptual space within which perception and actions occur.To reveal the underlying mechanisms of the visual perception of distance, we focus on the visual system’s intrinsic bias. We tested observers in a series of four studies to investigate how angular declination below the horizon a, eye height H, and the geographical slant of intrinsic bias 6 affect judged distance under various stimulus conditions. The intrinsic bias is revealed in the dark without external depth cue. In the four studies conducted, we investigated the influence of intrinsic bias on space perception, as well as how top-down attention and intrinsic bias together affects space perception in the reduced-cue condition. We also investigate how the visual system derives the intrinsic bias.In Chapter 2, we measured the intrinsic bias using the "blind walking gesture height" task, which was used by He, Ooi and their colleagues. Just as they found in previous studies, observers located the target at the intersection of the projection line from the eye to the target and the intrinsic bias, which reflects the internal representation of the ground surface.In chapter 3, we focused on the influence of the intrinsic bias on target size judgment. In the dark, we employed the matching task and the "blind walking gesturing the height and size" task simultaneously to study the relationship between intrinsic bias, distance perception and size perception. In Exp 3.1, we used the size matching task and found size perception in the dark was also affected by the intrinsic bias. In Exp 3.2, we retested the subjects using an action task, and found both the distance perception and size perception in the dark were affected by the intrinsic bias. In Exp 3.3, we found that the explicit knowledge of the target size had a significant effect on egocentric distance perception.In Chapter 4, we investigated the origin of the intrinsic bias, and how the eye height affects the intrinsic bias. We tested subjects in the dark environment, in the reduced-cue-environment, and in the full-cue environment, to compare the different egocentric distance performance between tall and short subjects, in the upper and lower visual fields. In the dark, the intrinsic bias was vertically asymmetric about the eye level in both action and perception task. The tall subjects showed a larger asymmetry, with the intrinsic bias in the lower field been further from the eye. In the reduced cue environment, in the presence of ground or ceiling texture background surface was given, the vertical asymmetric was more obvious, revealing ground superiority in both tasks. In the dark and reduced-cue environment, the larger eye height of the tall subjects significantly improved the accuracy of egocentric distance perception. In the bright natural environment with full cue, the tall and short subjects showed no difference in egocentric distance judgment using the blind-walking task. However, exocentric distance judgment task showed significant eye height superiority in the tall subjects. The results are consistent with the hypothesis that the intrinsic bias was obtained from past experiences of the statistical spatial relationship between the observer and ground surface.In Chapter 5, we investigated whether top-down attention plays a role in perceptual space formation. Overt attention deployment was controlled by fixating directly at the fixation point with the fovea, while the covert attention was directed to the upper or lower visual field. Egocentric distance judgment performances under attentional or inattentional conditions were compared. The results showed that paying attention to the ground texture background significantly improved the accuracy of distance perception. Both the action and perception task showed the same evidence, that top-down attention plays an important role in the representation the ground surface and construction of visual perceptual space.In summary, over a series of 4 studies, we revealed the characteristics of the intrinsic bias, showed it influences size perception, found evidence for its origin being associated with past experiences, and showed top-down attention can affect space perception in the reduced-cue-environment. These findings lead us to conclude that the visual system relies on the external depth information in the visual scene and its intrinsic bias to construct a global ground surface representation for space perception. The visual system’s intrinsic bias is obtained from past experiences of the statistical spatial relationship between the observer and ground surface. When lacking of external cues, the visual system uses the intrinsic bias as a default representation of the ground. When the external depth cues are present but sparse, the intrinsic bias integrate with the attended external depth cues to form the perceptual space.