Abstract
Direct gaze is a powerful social cue able to capture the onlooker’s attention. Beside gaze, head and limb movements as well can provide relevant sources of information for social interaction. This study investigated the joint role of direct gaze and hand gestures on onlookers corticospinal excitability (CE). In two experiments we manipulated the temporal and spatial aspects of observed gaze and hand behavior to assess their role in affecting motor preparation. To do this, transcranial magnetic stimulation (TMS) on the primary motor cortex (M1) coupled with electromyography (EMG) recording was used in two experiments. In the crucial manipulation, we showed to participants four video clips of an actor who initially displayed eye contact while starting a social request gesture, and then completed the action while directing his gaze toward a salient object for the interaction. This way, the observed gaze potentially expressed the intention to interact. Eye tracking data confirmed that gaze manipulation was effective in drawing observers’ attention to the actor’s hand gesture. In the attempt to reveal possible time-locked modulations, we tracked CE at the onset and offset of the request gesture. Neurophysiological results showed an early CE modulation when the actor was about to start the request gesture looking straight to the participants, compared to when his gaze was averted from the gesture. This effect was time-locked to the kinematics of the actor’s arm movement. Overall, data from the two experiments seem to indicate that the joint contribution of direct gaze and precocious kinematic information, gained while a request gesture is on the verge of beginning, increases the subjective experience of involvement and allows observers to prepare for an appropriate social interaction. On the contrary, the separation of gaze cues and body kinematics can have adverse effects on social motor preparation. CE is highly susceptible to biological cues, such as averted gaze, which is able to automatically capture and divert observer’s attention. This point to the existence of heuristics based on early action and gaze cues that would allow observers to interact appropriately.
Highlights
In humans, eye contact may signal an approaching intention from the gazer toward the perceiver, and it is critical for communication and social interactions (Kleinke, 1986; Senju and Johnson, 2009; Schilbach et al, 2013; Hamilton, 2016)
Direct Gaze compared to Object Gaze conditions increased the scoring for Items Q1 (“I felt involved in the action”; t(224) = −4.51, p < 0.001) and Q3 (“At the end of the video, I had the impression that the boy wanted to interact with me”; t(224) = −5.78, p < 0.001)
The results from Experiment 1 showed no effect on corticospinal excitability (CE) when presenting a request gesture accompanied by a direct gaze to the observer, nor when the actor’s gaze was convergent with the direction of his gesture
Summary
Eye contact may signal an approaching intention from the gazer toward the perceiver, and it is critical for communication and social interactions (Kleinke, 1986; Senju and Johnson, 2009; Schilbach et al, 2013; Hamilton, 2016). Eye contact is so relevant in social development that a failure to develop typical gaze behavior is one of the earliest signals of social disorders, such as autism (BaronCohen, 1995a; Hamilton, 2016). Observing another’s averted gaze can trigger in the onlooker a rapid and automatic shift of attention toward the gazed direction (e.g., Driver et al, 1999; Langton and Bruce, 1999; Friesen et al, 2005)
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