Visual guidance of locomotor interception is based on nulling changes in target bearing (not egocentric target direction nor target-heading angle).

In two experiments we studied how participants steer to intercept uniformly moving targets in a virtual driving task under hypotheses-differentiating conditions of initial target eccentricity and target motion. In line with our re-analysis of findings from earlier studies, in both experiments the observed interception behavior could not be understood as resulting from reliance on (changes in) egocentric target direction nor from reliance on (changes in) target-heading angle. The overall pattern of results observed was however compatible with a control strategy based on nulling changes in the target's bearing angle. The presence of reversals in movement direction under specific combinations of target eccentricity and motion conditions indicated that the information used was not purely rate-of-change (i.e., first-order) based but carried traces of an influence of initial target position. In Experiment 2 we explicitly tested the potential role of early reliance on perceived egocentric target direction by examining the effects of a 10° rotation of the visual scene (i.e., of both target and environment). While such a rotation gave rise to minor changes in the moment of initiation of the first steering action, contrary to predictions it did not affect the characteristics of the direction-reversal phenomenon. We conclude that the visual guidance of locomotor interception is best understood as resulting from nulling changes in the target's bearing angle, with such nulling perhaps best conceived as being fractional-order (rather integer-order) driven.

Reversals in Movement Direction in Locomotor Interception of Uniformly Moving Targets.

Here we studied how participants steer to intercept uniformly moving targets in a virtual driving task. We tested the hypothesis that locomotor interception behavior cannot fully be explained by a strategy of nulling rate of change in pertinent agent-target relations such as the target-heading angle or target's bearing angle. In line with a previously reported observation and model simulations, we found that, under specific combinations of initial target eccentricity and target motion direction, locomotor paths revealed reversals in movement direction. This phenomenon is not compatible with unique reliance on first-order (i.e., rate-of-change based) information in the case of uniformly moving targets. We also found that, as expected, such reversals in movement direction were not observed consistently over all trials of the same experimental condition: their presence depended on the timing of the first steering action effected by the participant, with only early steering actions leading to reversals in movement direction. These particular characteristics of the direction-reversal phenomenon demonstrated here for a locomotor interception-by-steering task correspond to those reported for lateral manual interception. Together, these findings suggest that control strategies operating in manual and locomotor interception may at least share certain characteristics.

Perceptual post-effects of left neck muscle vibration with visuo-haptic feedback in healthy individuals: A potential approach for treating spatial neglect.

Among the techniques used to reduce spatial neglect's symptoms, left neck muscle vibration (NMV) is alluring because it does not require the patient's attentional co-operation. The aim of this study was to determine the type of NMV-associated feedback that induced the most intense and longest-lasting egocentric post-effects. Eighty-seven healthy individuals were randomly assigned to four intervention groups: "neck muscle vibration, blindfolded" (NMV), "neck muscle vibration with vision" (NMV + V), "neck muscle vibration and visual finger-pointing" (NMV + P), and "visual finger-pointing" (P). An eyes-closed finger-pointing subjective straight-ahead (SSA) test was carried out before the intervention, immediately afterwards, and 30 min afterwards. The results showed that only the NMV + P intervention induced a lasting leftward bias of SSA. In addition, the deviation reported in this intervention group differed significantly from those observed in the other interventions. The combination of visuo-haptic feedback and neck-somatosensory stimulation may enable a full, lasting intermodal recalibration, which could be potentiated by the attention level engaged during voluntary pointing. These outcomes highlighted that the NMV technique could easily integrate into routine occupational therapy sessions for treating various aspects of neglect disorders.