Social cues, such as direction of eye gaze and head angle, are effective in redirecting one’s attention to salient aspects of the environment (Friesen and Kingstone, 1998; Driver et al., 1999; Langton and Bruce, 1999; Hoffman and Haxby, 2000; Pelphrey et al., 2003; Senju and Csibra, 2008; Senju and Johnson, 2009). Here, we investigated whether reallocation of spatial attention was faster in response to the shift in eye gaze of a familiar individual as compared to the shift in eye gaze of a stranger.

Several studies have demonstrated that perceived eye gaze spontaneously biases spatial attention in the direction of the gaze (Friesen and Kingstone, 1998; Driver et al., 1999; Langton and Bruce, 1999; Hoffman and Haxby, 2000; Pelphrey et al., 2005; Frischen et al., 2007; Senju and Csibra, 2008; Senju and Johnson, 2009). These biases in spatial attention have previously been shown to be susceptible to top-down influences (Teufel et al., 2010; Kawai, 2011; Wiese et al., 2012, 2014; Wykowska et al., 2014). The neural mechanisms underlying gaze perception have been studied extensively. fMRI studies have shown that specific regions, such as the posterior and anterior superior temporal sulcus, the intraparietal sulcus, the medial prefrontal cortex, are preferentially engaged by eye gaze and head angles, highlighting how dedicated populations of neurons are involved in processing these social cues (Hoffman and Haxby, 2000; Pageler et al., 2003; Pelphrey et al., 2003; Engell and Haxby, 2007; Carlin et al., 2012; Carlin and Calder, 2013; and for a review, Senju and Johnson, 2009). Interestingly, eye gaze and head position are processed even without awareness, underscoring that detection of these features, and the subsequent effect on spatial attention, can be preconscious and any facilitation or slowing by familiarity may be acting upon a very early stage of processing (Stein et al., 2011; Gobbini et al., 2013a).

Personally familiar faces are highly salient social stimuli (Gobbini and Haxby, 2007). Efficient face processing through multimodal experience with familiar others serves to facilitate interactions with those who are most important in our social lives. Familiarity affords more efficient face detection and recognition of identity (Bruce et al., 1994; Burton et al., 1999; Jenkins et al., 2011; Ramon et al., 2011; Gobbini et al., 2013b; Ramon, 2015; Visconti di Oleggio Castello and Gobbini, 2015; Ramon and Van Belle, 2016; Visconti di Oleggio Castello et al., 2016). Similarly, processing of social cues in faces, such as direction of attention, are markedly facilitated by familiarity. For example, in a study of perception of gaze direction and head angle, perception of eye gaze was detected around 100 ms faster in familiar as compared to the faces of strangers (Visconti di Oleggio Castello et al., 2014).

Here, we investigated whether personal familiarity with the faces whose change in eye gaze served as attentional cue has an influence on how we reallocate spatial attention in response to those eye gaze changes. We used a gaze cueing paradigm – an adaptation of the Posner cueing paradigm (Posner, 1980). In the Posner cueing paradigm, presentation of a directional cue (e.g., an arrow) precedes the onset of a target in either the cued or uncued direction. Participants are faster and more accurate in processing a target if it appears in the cued direction (Posner, 1980). In the gaze cueing paradigm, faces with directional eye gaze served as the directional cue for manipulating spatial attention. Perceived eye gaze has proved successful in modulating spatial attention in schematic faces (Friesen and Kingstone, 1998). One could hypothesize that facilitation of detection of eye gaze direction in personally familiar faces leads to more effective redirection of spatial attention as compared to detection of eye gaze shifts in the faces of strangers (Visconti di Oleggio Castello et al., 2014). As an alternative hypothesis, highly salient faces of familiar individuals could hold attention (Bindemann et al., 2005), thus making redirecting spatial attention slower, similar to a highly rewarding feature in visual search tasks (Hickey et al., 2010; Anderson et al., 2011; Hickey and Peelen, 2015; Munneke et al., 2015). Allocation of attentional resources is driven by relative salience of stimuli encountered in the environment, where high salience can be generated by the relative configuration of low-level features such as color, orientation and size in the scene (Itti and Koch, 2001; Soltani and Koch, 2010) or by an interaction between sensory features and reward (Markowitz et al., 2011; Theeuwes and Belopolsky, 2012; Khorsand et al., 2015). Similarly, valence of the face cue (e.g., faces with expression of emotion such as fear, happy, neutral, or sad or one’s own face; Pourtois et al., 2013; Pérez-Duenas et al., 2014; Porciello et al., 2014) has been shown to modulate the magnitude of attentional capture. Thus, spatial reallocation of attention in response to gaze shifts in familiar faces could be facilitated by faster processing of the gaze cue or slowed by the social saliency of familiar faces.

We tested these two competing hypotheses on how face familiarity interacts with redirection of attention in response to shifts in eye gaze with two experiments. In the first experiment, we asked participants to make a saccade to the target appearing in the periphery either on the right or on the left of a centrally presented face. In the second experiment, we asked the participants to report the side on which the target appeared with a button press, without looking away from the centrally presented face. We used the manual response paradigm to test whether slowed initiation of saccades to a target is attributable to the difficulty of breaking fixation from salient centrally presented faces. Finally, we performed a control experiment to ensure that results from the first two experiments on reallocation of attention were not due to differences in detecting eye movements in personally familiar and unfamiliar faces (Visconti di Oleggio Castello et al., 2014). In this experiment, we measured participants’ speed in detecting a change in the direction of eye gaze in personally familiar and unfamiliar faces.

In Experiment 1, we investigated attention shifts elicited by the eye gaze of familiar and unfamiliar faces using a target-detection task based on the Posner cueing paradigm, with saccadic reaction time (SRT) as the dependent variable. Participants saw a directional gaze cue to the left or right in a familiar or unfamiliar face followed by a peripheral target that could appear on either side of the fixation cross. They were instructed to saccade toward the target as soon as it appeared on the screen. We manipulated the familiarity of the face cue, the congruence between the cue and target direction, and the delay between the cue and the target onset. Participants were instructed to be as fast as possible in their response, but not at the expense of accuracy.

In this experiment, we investigated whether findings reported in Experiment 1 would hold if the response to the attended target did not involve explicit eye movements away from the centrally presented face cue, we tested the same participants in a paradigm that involved a manual response via a button press.

In order to ensure that the results reported in Experiments 1 and 2 did not come from differences in processing the eye gaze from familiar and unfamiliar faces, we asked participants to indicate the direction of eye gaze changes in familiar and unfamiliar faces with a manual response.

We tested the interaction between reallocation of spatial attention mediated by shifts in eye gaze and personal familiarity with faces. We used an adapted version of the Posner paradigm to study attention shifts elicited by eye gaze movements in others. Overall, the results showed facilitation of responses to peripheral targets in trials with congruent cues as compared to trials with incongruent cues. These results replicate the effect of cue validity on saccadic response time found in prior research (Kuhn and Kingstone, 2009). Consistent with earlier studies, reaction times were faster and the cue validity effect was larger at the longer SOA of 200 ms (Friesen and Kingstone, 1998; Kuhn and Kingstone, 2009). Here, we report for the first time an interaction of SOA and personal familiarity wherein face familiarity slows the redirection of spatial attention mediated by eye gaze at short but not long SOAs. More specifically, in our first experiment we found that gaze shifts in personally familiar faces, as compared to in unfamiliar faces, elicited slower saccadic response times at a short SOA of 100 ms between the gaze shift and the onset of the peripheral target. Familiarity did not modulate the effect of cue validity. No modulation by familiarity was recorded at the longer SOA of 200 ms, indicating that the slowing of attention shifts due to cue face familiarity is brief. The results of the second experiment, which required maintaining fixation on the cue face and manual responses, showed that the effect of familiarity was not specific to saccadic responses that required looking away from the face. The size of the familiarity effect, however, was smaller than for saccadic responses. The additional time to prepare a manual response (over 150 ms) may diminish the familiarity effect, which appears to be rapidly fading.

The third experiment investigated whether the results reported in Experiments 1 and 2 were due to differences in processing of eye gaze in familiar and unfamiliar faces, rather than to differences in the holding of attention by familiar and unfamiliar faces. Results from Experiment 3 showed that personal familiarity significantly facilitated detection of the direction of gaze shifts, as compared to unfamiliar faces, indicating that the familiarity effect on gaze-cued attention shifts to the periphery, which was in the opposite direction, is not due to slower detection of the gaze cue itself. Interestingly, the facilitation of eye gaze detection by familiarity appears to be stronger for more demanding tasks. In a visual search task, we found a larger effect of facilitation on RT, over 100 ms (Visconti di Oleggio Castello et al., 2014). By contrast, we found only a non-significant trend toward facilitation in a simple gaze change detection task (see Supplementary Material) unlike the task in Experiment 3 that required indicating the gaze change direction. Therefore, despite facilitated detection of eye gaze shifts in familiar faces, reallocation of attention away from the face is slowed by personal familiarity due to slowed disengagement of attention.

To summarize, our results indicate that familiarity delays gaze-cued attentional shifts at short latencies by briefly slowing deployment of attention away from familiar faces. Our results suggest that the familiar faces capture attention (Simons, 2000), and that this effect fades quickly. Slowed disengagement of attention from the familiar faces overrides any advantage of faster detection of gaze changes in familiar, as compared to unfamiliar faces. Holding of attention by personally familiar faces also has been shown by others with a different experimental paradigm, namely visual search (Devue et al., 2009).

The relationship of social salience and bias of spatial attention has been studied using personally familiar faces but with a different degree of familiarity as compared to the personally familiar faces chosen for our experiments. In previous studies, faces of colleagues or coworkers have been used as familiar stimuli. For example, Hungr and Hunt (2012) used one’s own face and a familiar confederate –the face of the experimenter– as familiar faces, and Deaner et al. (2007) used faces of professors, postdoctoral researchers and graduate students from the same department of the participants. Hungr and Hunt (2012) reported faster reaction times in the gaze cueing paradigm for the confederate’s faces, and longer for one’s own face and for faces of strangers. Deaner et al. (2007) reported a complex interaction for gender and familiarity with faster reaction times in women when participants were cued by familiar faces. In our experiments, we aimed to study the effect of familiarity that is characterized by a personal, close relationship with repeated social interactions over time rather than simple prior visual exposure. Personally familiar individuals with whom we have a close relationship have a special status and are processed more efficiently as compared to other type of familiar faces, such as famous faces and visually familiar faces. Therefore, we chose as stimuli, the faces of friends with whom the participants had a good close relationship for at least a year.

Our results provide evidence for slowed disengagement of attention from personally familiar faces, a highly salient social stimulus. The effect of slowed disengagement of attention was only found for familiar faces at a short delay between the cue and the target. Interestingly, studies of blocking by salient cues in associative learning (Denton and Kruschke, 2006; Le Pelley et al., 2014) and attentional capture by cues of high valence (Hickey et al., 2010; Anderson et al., 2011) lend support to the idea that a centrally presented cue that is highly salient, as compared to cues of less salience, leads to slower redirection of attention rather than serving as a more informative cue. Our results are consistent with these studies that used cues other than faces. Repeated exposure to the faces of familiar individuals and the semantic and emotional information associated with these identities make them socially salient. In our study, we demonstrate that this highly salient social cue holds attention rather than facilitates redirection of attention.

MIG conceived the idea for the study. VC, MIG, and AS designed the experiment. VC collected and analyzed the data. MVdOC provided suggestions for data analysis. VC prepared the manuscript, MIG, MVdOC, and AS provided critical inputs to the final version of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.