Social Attention Following Gaze Direction: Underlying Mechanisms, Development and Individual Differences

Abstract

The eyes are one of the most valuable sources of social information for human beings. It is commonly said that 'the eyes are the window to the soul' as they help us infer the thoughts, emotions, and behavior of others. The importance of gaze is evident both at a phylogenetic and ontogenetic level. Human eyes have a unique morphology among primates, with a white and uniform sclera that allows for quick detection of gaze direction (Kano et al., 2022; Kobayashi & Kohshima, 2001). This special ability in processing eyes is present from birth. Infants show an early preference for faces (Farroni et al., 2005; Johnson et al., 1991) and can distinguish between direct and averted gazes (Farroni et al., 2002, 2004). Over time, gaze direction becomes an increasingly precise attentional cue regarding the object of interest for others. With experience and brain development, these early skills prompt a cascade of cognitive processes such as joint attention, language, and theory of mind, which are central aspects in the diagnosis, prognosis, and intervention of autism spectrum disorders (Mundy, 2018). Attentional mechanisms in response to gaze direction have sparked a scientific interest. In particular, there is a debate about whether gaze is processed through domain-general mechanisms similar to other nonsocial stimuli that also orient attention, such as arrows, or if it is processed through a special system. Although both stimuli yield similar orienting effects (Chacón-Candia, Román- Caballero, et al., 2023), gaze may trigger additional social mechanisms in later stages of processing (Edwards et al., 2022; Gregory & Jackson, 2017; Marotta et al., 2019). To capture these qualitative differences, it is necessary to use experimental procedures that are sensitive to effects beyond shared attentional properties. The studies comprising this thesis are based on a spatial interference paradigm that consistently differentiates the attentional effects produced by gaze from those generated by arrows (Cañadas & Lupiáñez, 2012; Hemmerich et al., 2022; Ishikawa et al., 2022; Jones, 2015; Marotta et al., 2018). Specifically, gaze elicits an opposite spatial congruency effect compared to other nonsocial stimuli. This distinctive reversed congruency effect of gaze may serve as an indirect index of social attention, a phenomenon we aim to comprehend and analyze in the following chapters. Therefore, the primary objective of this thesis is to investigate to what extent and through which mechanisms gaze triggers specific attentional processes. We approach this goal from three complementary perspectives. First, we aim to understand the underlying mechanism of the reversed congruency effect shown by eye gaze. One possibility is that gaze processing activates intentionality. On the one hand, perceiving someone with an averted gaze would shift our attention in the looked direction in the same way as perceiving an arrow. However, gaze may also prepare the attentional system to select the potential object of interest that the other person is attending to. Through the two studies presented in Chapter 3, we thoroughly explore this hypothesis by investigating the influence of a possible joint distraction effect that occurs when the eyes look outward, away from the task context. Second, we seek to clarify the contribution of social factors by analyzing the interaction of this effect with other socio-cognitive variables. Chapter 4 examines the influence of emotions on the reversed effect of gaze and its interaction with individual differences in the level of autistic traits. A third key aspect of understanding the differences between arrows and gaze stems from a developmental perspective. Chapter 5 addresses how and when these processes emerge, considering the period from childhood to adolescence. The observed results align with previous literature (Hemmerich et al., 2022; Itier & Batty, 2009; Marotta et al., 2019) regarding the presence of an initial shared processing phase for eyes and arrows, followed by additional high-level processes specifically linked to gaze. Common attentional mechanisms appear to be present in 4-year-old children, while the gaze effect may gradually develop and reach the adult pattern in early adolescence. Our findings also indicate that other social factors, such as a facial expression of happiness, enhance the magnitude of the effect; an interaction that is not observed in individuals with a high level of autistic traits. In this complex interplay, mere perception and object identification may not be sufficient to counteract the presumed joint distraction mechanism. The overall data do not confirm the current joint distraction hypothesis. However, Chapter 6 delves into a comprehensive exploration of various expanded frameworks, encompassing the existence of an additional mechanism associated with gaze direction processing, which would gradually refine during infancy and be influenced by both social qualities of the context and individual characteristics.