Peripersonal versus extrapersonal visual scene information for egocentric direction and position perception.

When perceiving the visual environment, people simultaneously perceive their own direction and position in the environment (i.e., egocentric spatial perception). This study investigated what visual information in a scene is necessary for egocentric spatial perceptions. In two perception tasks (the egocentric direction and position perception tasks), observers viewed two static road images presented sequentially. In Experiment 1, the critical manipulation involved an occluded region in the road image, an extrapersonal region (far-occlusion) and a peripersonal region (near-occlusion). Egocentric direction perception was worse in the far-occlusion condition than in the no-occlusion condition, and egocentric position perceptions were worse in the far- and near-occlusion conditions than in the no-occlusion condition. In Experiment 2, we conducted the same tasks manipulating the observers' gaze location in a scene-an extrapersonal region (far-gaze), a peripersonal region (near-gaze) and the intermediate region between the former two (middle-gaze). Egocentric direction perception performance was the best in the far-gaze condition, and egocentric position perception performances were not different among gaze location conditions. These results suggest that egocentric direction perception is based on fine visual information about the extrapersonal region in a road landscape, and egocentric position perception is based on information about the entire visual scene.

Egocentric Direction and Position Perceptions are Dissociable Based on Only Static Lane Edge Information.

When observers perceive several objects in a space, at the same time, they should effectively perceive their own position as a viewpoint. However, little is known about observers' percepts of their own spatial location based on the visual scene information viewed from them. Previous studies indicate that two distinct visual spatial processes exist in the locomotion situation: the egocentric position perception and egocentric direction perception. Those studies examined such perceptions in information rich visual environments where much dynamic and static visual information was available. This study examined these two perceptions in information of impoverished environments, including only static lane edge information (i.e., limited information). We investigated the visual factors associated with static lane edge information that may affect these perceptions. Especially, we examined the effects of the two factors on egocentric direction and position perceptions. One is the "uprightness factor" that "far" visual information is seen at upper location than "near" visual information. The other is the "central vision factor" that observers usually look at "far" visual information using central vision (i.e., foveal vision) whereas 'near' visual information using peripheral vision. Experiment 1 examined the effect of the "uprightness factor" using normal and inverted road images. Experiment 2 examined the effect of the "central vision factor" using normal and transposed road images where the upper half of the normal image was presented under the lower half. Experiment 3 aimed to replicate the results of Experiments 1 and 2. Results showed that egocentric direction perception is interfered with image inversion or image transposition, whereas egocentric position perception is robust against these image transformations. That is, both "uprightness" and "central vision" factors are important for egocentric direction perception, but not for egocentric position perception. Therefore, the two visual spatial perceptions about observers' own viewpoints are fundamentally dissociable.

Independence of egocentric and exocentric direction processing in visual space

One major issue concerning investigations of visual perception is determination of the geometrical properties of visual space. To address this issue, one must determine the relationships between geometrical features of visual space, distance, direction, angle, and size. Consistent evidence indicates that visual angle is a determinant of perceived exocentric distance. Previous evidence suggests that exocentric distance and direction are hierarchically processed, with distance preceding direction. The present study investigated the relationship between the perceptual processing of egocentric direction and exocentric direction using a task that independently provides both perceptual variables in a single judgment. The results indicated that egocentric directions were systematically overestimated, and this was not caused by either the global shape of the layout or leg length effects. Exocentric directions presented a discontinuous pattern of overestimation of smaller angles that were subtended by radial orientations and accuracy of right angles that were subtended by horizontal orientations. This could be explained by the anisotropy of visual space, a well-established phenomenon from visual space studies. The analysis of the association between the processing of these two variables revealed independence between them in which exocentric direction processing did not depend on the processing of egocentric direction processing, and vice versa. The present results and prior evidence converge on the notion of hierarchical processing in which the visual system processes the egocentric distance of objects followed by exocentric distance processing and subsequent processing. The precise positions of egocentric and exocentric directions in this chain of processing remain to be determined.

Independence of egocentric and exocentric direction processing in visual space

One major issue concerning investigations of visual perception is determination of the geometrical properties of visual space. To address this issue, one must determine the relationships between geometrical features of visual space, distance, direction, angle, and size. Consistent evidence indicates that visual angle is a determinant of perceived exocentric distance. Previous evidence suggests that exocentric distance and direction are hierarchically processed, with distance preceding direction. The present study investigated the relationship between the perceptual processing of egocentric direction and exocentric direction using a task that independently provides both perceptual variables in a single judgment. The results indicated that egocentric directions were systematically overestimated, and this was not caused by either the global shape of the layout or leg length effects. Exocentric directions presented a discontinuous pattern of overestimation of smaller angles that were subtended by radial orientations and accuracy of right angles that were subtended by horizontal orientations. This could be explained by the anisotropy of visual space, a well-established phenomenon from visual space studies. The analysis of the association between the processing of these two variables revealed independence between them in which exocentric direction processing did not depend on the processing of egocentric direction processing, and vice versa. The present results and prior evidence converge on the notion of hierarchical processing in which the visual system processes the egocentric distance of objects followed by exocentric distance processing and subsequent processing. The precise positions of egocentric and exocentric directions in this chain of processing remain to be determined.(AU)

Influence of optic flow on the control of heading and target egocentric direction during steering toward a goal.

Although previous studies have shown that people use both optic flow and target egocentric direction to walk or steer toward a goal, it remains in question how enriching the optic flow field affects the control of heading specified by optic flow and the control of target egocentric direction during goal-oriented locomotion. In the current study, we used a control-theoretic approach to separate the control response specific to these two cues in the visual control of steering toward a goal. The results showed that the addition of optic flow information (such as foreground motion and global flow) in the display improved the overall control precision, the amplitude, and the response delay of the control of heading. The amplitude and the response delay of the control of target egocentric direction were, however, not affected. The improvement in the control of heading with enriched optic flow displays was mirrored by an increase in the accuracy of heading perception. The findings provide direct support for the claim that people use the heading specified by optic flow as well as target egocentric direction to walk or steer toward a goal and suggest that the visual system does not internally weigh these two cues for goal-oriented locomotion control.