Predictive extrapolation of observed body movements is tuned by knowledge of the body biomechanics.

After a moving object has disappeared, observers typically mislocate its final position to where that object would have been if it had briefly continued to move. Previous studies have shown that this "forward displacement" (FD) is significantly smaller when observers see an upper-limb movement directed away from the body that would have been biomechanically impossible to continue along the same trajectory after it has disappeared than when the movement is directed toward the body and would have been easy to continue. This finding has been argued to reflect an implicit influence of observers' biomechanical knowledge on FD. However, this effect could also result from a "landmark attraction", which has been shown to reduce the size of displacement when an object moves away, rather than toward, from a landmark. To discriminate these possibilities, we measured the FD elicited by arm movements directed away or toward the body, which would have been biomechanically impossible or easy to continue after the stimuli disappeared, and by highly similar movements of geometrical shapes. In 2 experiments, we found a significantly larger effect of movement direction for the human stimuli. Thus, knowledge of the body biomechanics influences FD for body movements. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Shifting attention in visuospatial short-term memory does not require oculomotor planning: Insight from congenital gaze paralysis.

Attention allows pieces of information stored in visuospatial short-term memory (VSSTM) to be selectively processed. Previous studies showed that shifts of attention in VSSTM in response to a retro-cue are accompanied by eye movements in the direction of the position of the memorized item although there is nothing left to look at. This finding raises the possibility that shifts of attention in VSSTM are underpinned by mechanisms originally involved in the planning and control of eye movements. To explore this possibility, we investigated the ability of an individual with congenital horizontal gaze paralysis (HGP2) to shift her attention horizontally or vertically toward a memorized item within VSSTM using a retro-cue paradigm. As efficient oculomotor programming is not innate but requires some trial and error learning and adaptation to develop, congenital paralysis prevents this development. Consequently, if shifts of attention in VSSTM rely on the same mechanisms as those supporting the programming of eye movements, then horizontal congenital gaze paralysis should necessarily prevent typical retro-cueing effect in the paralyzed axis. At odds with this prediction, HGP2 showed a typical retro-cueing effect in her paralyzed axis. This original finding indicates that selecting an item within VSSTM does not depend on the ability to program a saccade.