Non-predictive stimuli are integrated during multisensory goal-directed reaching with or without explicit awareness


According to the modality appropriateness hypothesis participants choose to focus on the preferred modality (vision) when completing spatial versus temporal tasks. It is unknown if participants can ignore the preferred modality if the information is not informative. The present experiment examined if explicit instructions regarding the validity of a secondary (visual) stimulus affects how goal-directed movements to an auditory target are performed. Twenty-two participants were instructed to point at the location of one of two sound targets (200ms white noise) located in right and left hemi-space (recorded using Optotrak 3D Investigator, 300Hz). Participants were split into two groups where half were not told and half were told (TG) that on 50% of trials a light appeared at the same location as the sound and on 50% of trials they appeared at opposite locations. Reaction time (RT), movement time, peak velocity (PV) and time to PV were similar in both groups. For the TG the proportion of time spent before PV was greater. The TG had reduced time for online corrections, and maintained the same level of endpoint accuracy without increased time for planning. Kinematic variables showed no group differences, however, movements towards congruent targets had lower variability during peak deceleration and end point location. Awareness of the equivocal probability of spatial congruency improved the effectiveness of the movement plan. However, regardless of awareness of the validity of the secondary stimulus, movements in the congruent condition were less variable at the end of the movement, indicating participants' consistently integrated multisensory stimuli.

Acknowledgments: Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), Research Manitoba, and the Canadian Foundation for Innovation