Tool use changes multisensory interactions in seconds: evidence from the crossmodal congruency task

Abstract

Active tool use in human and non-human primates has been claimed to alter the neural representations of multisensory peripersonal space. To date, most studies suggest that a short period of tool use leads to an expansion or elongation of these spatial representations, which lasts several minutes after the last tool use action. However, the possibility that multisensory interactions also change on a much shorter time scale following or preceding individual tool use movements has not yet been investigated. We measured crossmodal (visual-tactile) congruency effects as an index of multisensory integration during two tool use tasks. In the regular tool use task, the participants used one of two tools in a spatiotemporally predictable sequence after every fourth crossmodal congruency trial. In the random tool use task, the required timing and spatial location of the tool use task varied unpredictably. Multisensory integration effects increased as a function of the number of trials since tool use in the regular tool use group, but remained relatively constant in the random tool use group. The spatial distribution of these multisensory effects, however, was unaffected by tool use predictability, with significant spatial interactions found only near the hands and at the tips of the tools. These data suggest that endogenously preparing to use a tool enhances visual-tactile interactions near the tools. Such enhancements are likely due to the increased behavioural relevance of visual stimuli as each tool use action is prepared before execution.

Figure 1

Schematic account of spatial modulations in the crossmodal congruency effect (CCE). The effects are illustrated for a left hand index finger target (the ‘lightning strike’), however the congruency and spatial relationships apply to all four possible target positions. The dashed ellipses schematically represent the approximate proposed shape and size of the ‘peri-hand’ area. The circles represent a ‘congruent’ visual distractor - presented next to the same digit (the same elevation in the task - either ‘upper’ or ‘lower,’ when the hands are holding the tools). The stars represent incongruent visual distractors. Filled symbols represent targets and distractors on the same tool. Open symbols represent target and distractors on different tools. Performance is, on average, worse in incongruent trials with respect to congruent trials. Most importantly, however, this crossmodal congruency effect is larger when target and distractor stimuli are presented on the same side of space (the same hand) relative to when they are presented on different sides (hands).

Figure 2

Spatial modulation of crossmodal congruency effects during tool use. Columns show the between-participants mean±SE of data from 60 participants. Filled columns - visual distractor and vibrotactile target presented on the same side (same tool). Open columns - visual distractor and vibrotactile target presented on different sides (different tools). The data illustrate the significant interaction between congruency, distance, and side.

Figure 3

Crossmodal congruency effects in the regular and random tool use groups: Trial-by-trial analysis. Data points show the between-participants mean±SE of data from 30 participants. Filled black squares - regular tool use group. Open circles - random tool use group. The data illustrate the significant interaction between congruency, trial, and group.