Determination of target distance in a structured environment: Selection of visual information for action

In the literature relating to visuo-motor control, controversial data are found concerning the consequence of enriching the visual scene in the specification of the target's spatial coordinates. In this paper four experiments were carried out to unravel this issue. Based on spatio-temporal analysis of pointing movements carried out in an open loop condition, the effect of appending contextual elements in the vicinity of a visual target was investigated, taking into account (1) their location in the visual field, (2) the extent of the movement, and (3) their presence during the planning and/or execution period of the movement. Taken as a whole, results showed that enriching the visual scene gave rise to a decrease of perceptual underestimation of distance (with no effect on the direction parameter), as otherwise observed (dark environment). Though not deeply affecting reaction and movement time, this effect held whatever the target position, provided that the contextual elements were situated between the initial and terminal position of the hand trajectory. The magnitude of the effect was, however, dependent upon the space conferred to the visual context. Furthermore, a higher spatial performance was observed when the latter was provided during the planning of execution period of the movement. Both effects combined when contextual elements were provided during the entire movement, which suggests a continuous updating of target coordinates during the whole motor performance. Altogether these findings underline a dynamic aspect of space perception, originating, in part, in the functional use of contextual cues in the coding of target distance. They also suggest that, provided the visual environment is structured, the retinal signal is widely used in the perception of target distance in visuo-manual tasks.