What Makes Eye Contact Special? Neural Substrates of On-Line Mutual Eye-Gaze: A Hyperscanning fMRI Study

Experimental setup. A, LIVE condition: the face of Participant 1 is projected on the screen of Participant 2 in real time and vice versa, allowing a mutual exchange of information. B, REPLAY condition: the picture is projected on the screen with a 20 s delay; therefore, there is no mutual interaction between participants in real time. C, REST condition (baseline): no image is presented on the black screen. D, Sequence of presentation of the experimental conditions.

Evaluation of the motion energy time series representing eye-blinks. The red dots indicate the timing of the detected eye-blink.

Behavioral analysis. A, The number of eye-blinks per block. We omitted the first 5 s of each block because of instability of the recorded video induced by task switching; the number of eye-blinks was therefore calculated based on the succeeding 15 s. Each dot represents a data point. In the boxplot, the line dividing the box represents the median of the data, the ends represent the upper/lower quartiles, and the extreme lines represent the highest and lowest values excluding outliers. B, ΣNCR values. The integral of the NCR of each condition across the whole frequency range was calculated. is the ΣNCR from the time series of the participant’s facial movement to that of the partner during the LIVE condition. is the ΣNCR from the time series of the participant’s facial movement to that of the partner during the REPLAY condition. is the ΣNCR from the time series of the participant’s facial movement to that of the partner during the REST condition. is the ΣNCR from the time series from the participant’s delayed facial movement on the screen to the partner’s time series during the REPLAY condition. C, Enhanced ΣNCR values from the REST condition.

Brain regions exhibiting significantly greater activation in the LIVE condition than in the REPLAY condition. A, Cerebellar activation is overlaid on the coronal planes of the SUIT template (Diedrichsen, 2006; Diedrichsen et al., 2009). B, The activation in the ACC is superimposed on the T1-weighted high-resolution anatomic MRI normalized to the MNI template space in the sagittal (left), coronal (middle), and transaxial (right) planes that crossed at (6, 12, 40) in the MNI coordinate system (in mm). SUIT, Spatially unbiased infratentorial template.

Regions exhibiting greater effective connectivity from the ACC in the LIVE condition than in the REPLAY condition. The area outlined in white is the dAIC (Chang et al., 2013). X indicates the MNI coordinates (in mm).