Current studies on visuomotor decision making come to inconsistent conclusions regarding the optimality with which these decisions are made. When executing rapid reaching movements under uncertainty, humans tend to automatically select optimal movement paths that take into account the position of all potential targets (spatial averaging). In contrast, humans rarely employ optimal strategies when making decisions on whether to pursue two action goals simultaneously or prioritise one goal over another. Here, we manipulated whether spatial averaging or pre-selection of a single target would provide the optimal strategy by varying the spatial separation between two potential movement targets as well as the time available for movement execution. In Experiment 1, we aimed to determine the time needed to reach for targets with small and large separation between them and to measure baseline strategies under low time pressure. Given generous time limits, participants did not employ a pure averaging approach but instead tended to pre-select the target that was easiest to reach and corrected their movement path inflight if required. In Experiment 2, a strict time limit was set such that the optimal strategy to reach the correct target successfully depended on the separation between the potential targets: for small separations, there was enough time to employ averaging strategies, but higher success for larger separations required pre-selecting the final target instead. While participants varied in the strategies they preferred, none of them flexibly adjusted their movement strategies depending on the spatial separation of the targets. In Experiment 3, we confirm the bias towards targets that are easiest to reach and show that this comes at the expense of overall task success. The results suggest a strong tendency for humans to minimize immediate movement effort and a general failure to adapt movement strategies flexibly with changes in the task parameters.

Current studies on visuomotor decision making come to inconsistent conclusions regarding the optimality with which these decisions are made. When executing rapid reaching movements under uncertainty, humans seem to automatically select optimal movement paths that take into account the position of all potential targets (spatial averaging). In contrast, humans rarely employ optimal strategies when making decisions on whether to pursue two action goals simultaneously or prioritise one goal over another. Here, we manipulated whether spatial averaging or pre-selection of a single target would provide the optimal strategy by varying the spatial separation between two potential movement targets as well as the time available for movement execution. Experiment 1 provided a generous amount of time to reach the final target. Participants tended to pre-select the target that was easiest to reach and correct their movement path in-flight if required. In Experiment 2, a strict time limit was set, such that the optimal strategy depended on the separation between the potential targets: for small separations, there was sufficient time to employ averaging strategies, but higher success for larger separations required pre-selecting the final target instead. None of our participants adjusted their movement strategies with spatial separation, however. In Experiment 3, we confirm the bias towards targets that are easiest to reach and show that this comes at the expense of overall task success. The results suggest a strong tendency to minimize immediate movement effort, and a failure to flexibly adjust movement strategies to maximize the probability of success.

Employing a sensory conflict paradigm, previous research has found that vision and touch contribute, on average, equally to the visuo-tactile perception of surface texture. Our study aimed to, firstly, replicate the original findings using a comparable setup and stimulus set; secondly, examine whether equal modality contributions can also be observed on an individual basis (using a within-subject design); and thirdly, explore how visuo-tactile integration is affected by illumination angle (top vs. oblique). Participants explored a discrepant standard consisting of different abrasive papers by vision, touch, and using both modalities simultaneously, and subsequently had to find the closest visual, tactile, and visuo-tactile match from a set of matching stimuli. We replicated equal contribution from vision and touch across the whole sample in both illumination conditions. We also found considerable inter-individual variations in the modality contributions when the stimuli were illuminated from the top. Interestingly, this variation decreased under oblique illumination, with most participants showing an about-equal contribution from both modalities to the combined texture percept. These findings are consistent with the assumption that the perceived discrepancy between vision and touch was reduced under oblique illumination suggesting overall that visual and tactile information are only weighted equally within a certain range of experienced discrepancy. Outside this individual range, one of the modalities is weighted higher with no clear preference for either modality.

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Successful obstacle avoidance requires a close coordination of the visual and the motor systems. Visual information is essential for adjusting movements in order to avoid unwanted collisions. Yet, established obstacle avoidance paradigms have typically either focused on gaze strategies or on motor adjustments. Here we were interested in whether humans show similar visuomotor sensitivity to obstacles when gaze and motor behaviour are measured across different obstacle avoidance tasks. To this end, we measured participants’ hand movement paths when grasping targets in the presence of obstacles as well as their gaze behaviour when walking through a cluttered hallway. We found that participants who showed more pronounced motor adjustments during grasping also spent more time looking at obstacles during locomotion. Furthermore, movement durations correlated positively in both tasks. Results suggest considerable intra-individual consistency in the strength of the avoidance response across different visuomotor measures potentially indicating an individual’s tendency to perform safe actions.

Visually perceived roughness of 3D textures varies with illumination direction. Surfaces appear rougher when the illumination angle is lowered resulting in a lack of roughness constancy. Here we aimed to investigate whether the visual system also relies on illumination-dependent features when judging roughness in a crossmodal matching task or whether it can access illumination-invariant surface features that can also be evaluated by the tactile system. Participants () explored an abrasive paper of medium physical roughness either tactually, or visually under two different illumination conditions (top vs oblique angle). Subsequently, they had to judge if a comparison stimulus (varying in physical roughness) matched the previously explored standard. Matching was either performed using the same modality as during exploration (intramodal) or using a different modality (crossmodal). In the intramodal conditions, participants performed equally well independent of the modality or illumination employed. In the crossmodal conditions, participants selected rougher tactile matches after exploring the standard visually under oblique illumination than under top illumination. Conversely, after tactile exploration, they selected smoother visual matches under oblique than under top illumination. These findings confirm that visual roughness perception depends on illumination direction and show, for the first time, that this failure of roughness constancy also transfers to judgements made crossmodally.

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