Extra-personal gaze influences on the eye to hand spatial interference effect


Richardson and colleagues (2013) demonstrated occulo-manual spatial interference by finding that the finger trajectory in a vertical tapping task deviated toward the direction of a concurrent saccade. It was proposed that this was due to generalized motor planning strategy resulting in entrainment of the hand to the eyes. Human action observation research has shown that cortical motor planning structures are also recruited in action observation (e.g. Buccino et al. 2001; Decety et al. 1997), which can result in spatial interference (Kilner et al. 2003). We hypothesized that because motor planning structures are recruited in both observation and execution of action, simply observing the horizontal saccades of another person would cause sufficient recruitment of occulo-motor planning structures, that would result in finger tap trajectory deviations toward the direction of the observed saccade (but would not do so in a non-biological observation control condition). 19 participants performed 24 trials of vertical finger taps under three different visual conditions. They were required to: a) saccade horizontally between targets; b) fixate on a biological stimulus (i.e. a video of horizontally saccading human eyes); or c) fixate on a non-biological control stimulus (horizontally moving black dots) while tapping their finger to an auditory metronome beat presented at a 750ms intervals. Results from the saccading condition replicate Richardson et al’s (2013) entrainment effect. That is, finger taps deviated to the left when participants saccaded left, and to the right when executed with a rightward saccade. Contrary to expectations however, there was no entrainment induced by observing either the biological stimulus or the control stimulus. This suggests that competing motor plans (eyes and hands) are necessary to induce interference. Further, simply observing eye movements do not recruit the same occulo-motor planning networks as action execution.  

Acknowledgments: Funding Acknowledgements: NSERC