Embodied perception of reachable space: how do we manage threatening objects?

This study aimed at determining whether the size of reachable space is affected by the level of danger of some everyday manipulable objects. Two possibilities are examined: Dangerous objects affect the size of reachable space because of long-term semantic knowledge of their potential hurtful value or the on-line relation between objects’ dangerous attributes and the body. The experimental paradigm combined the danger value (dangerous/not dangerous) and the orientation of objects (e.g. pointing away from/towards the perceiver). Reachability judgments measured the size of peripersonal space, and perception of objects’ danger was estimated through questionnaires. Results revealed that, whatever the estimated level of objects’ danger, the extent of peripersonal space was reduced when the threatening part of dangerous objects was oriented towards participants, not when oriented away. This suggests that the characteristics of the here and now body-objects interaction are crucial in affecting the boundary of peripersonal space.     

Effect of structuring the workspace on cognitive and sensorimotor distance estimation: no dissociation between perception and action

Independent processing of visual information for perception and action is supported by studies about visual illusions, which showed that context information influences overtjudgment but not reaching attempts. The objection was raised, however, that these two types of performance are notdirectly comparable, since they generally focus on different properties of the visual input. The goal of the present study was to quantify the influence of context information (in the form of a textured background) on the cognitive and sensorimotor processing of egocentric distance. We found that the subjective area comprising reachable objects (probed with a cognitive task) decreased, whereas the amplitude of reaching movement (probed with a sensorimotor task) increased in the presence of the textured background with both binocular and monocular viewing. Directional motor performance was not affected by the experimental conditions, but there was a tendency for the kinematic parameters to mimic trajectory variations. The similar but opposite effects of the textured background in the cognitive and sensorimotor tasks suggested that in both tasks the visual targets were perceived as closer when they were presented in a sparse environment. A common explanation for the opposite effects was confirmed by the percentage of background influence, which was highly correlated in the two tasks. We conclude that visual processing for perception and action cannot be dissociated from context influence, since it does not differ when the tasks entail the processing of similar spatial characteristics.