When two worlds collide: the influence of an obstacle in peripersonal space on multisensory encoding

Abstract

Multisensory coding of the space surrounding our body, the peripersonal space, is crucial for motor control. Recently, it has been proposed that an important function of multisensory coding is that it allows anticipation of the tactile consequences of contact with a nearby object. Indeed, performing goal-directed actions (i.e. pointing and grasping) induces a continuous visuotactile remapping as a function of on-line sensorimotor requirements. Here, we investigated whether visuotactile remapping can be induced by obstacles, e.g. objects that are not the target of the grasping movement. In the current experiment, we used a cross-modal obstacle avoidance paradigm, in which participants reached past an obstacle to grasp a second object. Participants indicated the location of tactile targets delivered to the hand during the grasping movement, while a visual cue was sometimes presented simultaneously on the to-be-avoided object. The tactile and visual stimulation was triggered when the reaching hand passed a position that was drawn randomly from a continuous set of predetermined locations (between 0 and 200 mm depth at 5 mm intervals). We observed differences in visuotactile interaction during obstacle avoidance dependent on the location of the stimulation trigger: visual interference was enhanced for tactile stimulation that occurred when the hand was near the to-be-avoided object. We show that to-be-avoided obstacles, which are relevant for action but are not to-be-interacted with (as the terminus of an action), automatically evoke the tactile consequences of interaction. This shows that visuotactile remapping extends to obstacle avoidance and that this process is flexible.

Keywords: Multisensory; Peripersonal; Reaching; Tactile; Visual.

Fig. 1

Top: Schematic representation of the experimental setup, showing starting position (small blue circle), the target object (light grey circle) and the non-target object (dark circle). The lines show the locations of the forty virtual tripwires. Bottom: The five different conditions: From left to right: Visuotactile congruent, visuotactile incongruent, control, tactile congruent and tactile incongruent

Fig. 2

Mean performance scores in %Error across participants for the tactile (left) and visuotactile (right) trials in congruent (light) and incongruent (dark) conditions. Error bars are standard error of the mean

Fig. 3

Overview of absolute reaction times in the tactile (left) and visuotactile (right) trials for congruent (light) and incongruent (dark) conditions. The scatter plot represents mean scores for that tripwire location across participants. The lines represent the least mean squares regression lines to show the mean relation between space and absolute reaction time. Please note that the analysis reported in the results section was based on individual slopes

Fig. 4

Top Difference scores between participants’ reaction times to valid and invalid stimuli under visuotactile (left Panel) and tactile stimulation (right Panel) across space (cross-modal congruency effect, CCE). The solid lines indicate least mean squares regression lines which shows that space accounts for approximately 38% of variation in the visuotactile conditions, while only for approximately 3% in tactile conditions. Please note that these figures show the group fit for clarity, but analysis was based on individual slopes. Bottom: Top view of a typical hand movement (the average hand movement of all participants in the visuotactile congruent condition) with coloured dots indicating the average visuotactile CCE at each tripwire.

Fig. 5

average distance from the index finger to the obstacle at the different tripwire locations. Error bars depict minimum to maximum distance per tripwire location