This commentary complements the target article by drawing attention to a seemingly overlooked line of research and theorizing concerned with what may constitute the origins of knowledge attribution in humans. Specifically, much research has been dedicated to investigate the psychology of perceiving and responding to eye cues as a uniquely human form of social cognition. This research unanimously shows that much information about other minds can be gleaned from eyes and that this information guides social interactions and cooperative decision-making among humans (see Grossmann, Reference Grossmann2017, for a review).
First, comparative research suggests that humans, when compared to our closest living primate relatives the chimpanzees, possess a unique sensitivity to eyes and eye cues (Kano & Tomonaga, Reference Kano and Tomonaga2010; Tomasello, Hare, Lehmann, & Call, Reference Tomasello, Hare, Lehmann and Call2007). This human-specific sensitivity to eyes manifests itself by a more effective and broadened use of eye cues to detect attentional, emotional, and mental-state cues in others. This sensitivity relies upon the unique morphology of the human eyes characterized by their horizontally elongated form and exposed white sclera. Critically, neuroscience research indicates that this sensitivity to eyes is underpinned by a network of brain regions comprising the amygdala at the subcortical level and posterior superior temporal and medial prefrontal cortices at the cortical level, implicated in enhanced attention to eyes and the detection of attentional, emotional, and mental states from eye cues, respectively (Schilbach et al., Reference Schilbach, Timmermans, Reddy, Costall, Bente, Schlicht and Vogeley2013). Developmental research with infants points to the existence of increased attention to eyes in newborns and indicates that the processes involved in detecting attentional, emotional, and mental states from eyes emerge during the course of the first year of life (Grossmann, Reference Grossmann2017). Based on an integration of these findings, the theoretical argument has been advanced that eyes provide a basis for connecting with other minds (Grossmann, Reference Grossmann2017). In other words, processes related to privileged orientation and attention to the eyes may help with detecting the presence of other minds, and processes related to decoding information contained in the eye or eye region helps with tracking the contents of other minds, including others' knowledge states.
Second, the existing developmental cognitive neuroscience research with infants, which has not been discussed by Phillips et al. shows that the brain processes underpinning our ability to read other minds develop early in infancy. This is in line with mounting evidence from numerous behavioral studies attesting to infants' mind reading abilities and underlines that behavioral and neuroscience research converges on the notion that access to other minds is an important and early emerging feature of human social cognition. Moreover, the neuroimaging research demonstrates similarity in the brain processes engaged by human infants and adults when processing eye cues (Grossmann, Reference Grossmann2017). Based on this similarity, it seems unlikely that different mechanisms (representations) are at play in adults than in infants, further supporting the notion of the early developmental emergence of knowledge attribution. Yet the kind of mental-state understanding attributed to infants based on these neuroscience and behavioral findings does not require the infant to have an explicit (conceptual) grasp of other minds. Indeed, evidence is accumulating that eye-based social cognition might be rooted in automatic processes as demonstrated by neuroscientific research on subliminal face and gaze processing with human infants (Jessen & Grossmann, Reference Jessen and Grossmann2014, Reference Jessen and Grossmann2020).
Third, although the emphasis here was on the ontogenetic and brain origins of human-specific sensitive responding to eyes, eyes are certainly not the only route to understanding other minds. As pointed out by Phillips et al., other sources are also important for informing us about the presence and contents of other minds. For example, there is much research to show that humans use vocal cues in a very similar manner as they use facial and eye cues and sensitivity to voices emerges early in ontogeny (Grossmann, Oberecker, Koch, & Friederici, Reference Grossmann, Oberecker, Koch and Friederici2010). Furthermore, in certain contexts, vocal cues have been shown to provide more powerful information regarding another person's mind than facial cues (Schroeder & Epley, Reference Schroeder and Epley2015). Apart from vocal cues, humans may also rely on information provided through touch (Fairhurst, Löken, & Grossmann, Reference Fairhurst, Löken and Grossmann2014), although when compared to facial and vocal cues, touch as a means for gleaning insights into other minds has been relatively neglected.
From an evolutionary perspective, eye cues are considered to function particularly well during close range interactions without direct physical contact, which are characteristic for many collaborative activities in humans (Tomasello, Melis, Tennie, Wyman, & Herrmann, Reference Tomasello, Melis, Tennie, Wyman and Herrmann2012). This includes activities such as hunting and gathering (foraging), which is considered the primary and ancestral form of subsistence within the genus Homo. Compared to vocal signaling, coordination through eye cues has the advantage that it can occur silently, making it an ideal form of communication between cooperators during group activities such as gathering and hunting, when at the risk of being noticed by predators or prey. Despite the adaptive advantages with respect to human cooperative activities seen in adults, from a developmental perspective, an early emerging sensitivity to eyes might lay the foundation for being able to identify, choose between, and coordinate with cooperative partners.
In summary, we advocate for an approach that systematically and more mechanistically assesses the origins of knowledge about others by taking a developmental cognitive neuroscience perspective in order to advance a more complete understanding of how humans come to understand other minds.
This commentary complements the target article by drawing attention to a seemingly overlooked line of research and theorizing concerned with what may constitute the origins of knowledge attribution in humans. Specifically, much research has been dedicated to investigate the psychology of perceiving and responding to eye cues as a uniquely human form of social cognition. This research unanimously shows that much information about other minds can be gleaned from eyes and that this information guides social interactions and cooperative decision-making among humans (see Grossmann, Reference Grossmann2017, for a review).
First, comparative research suggests that humans, when compared to our closest living primate relatives the chimpanzees, possess a unique sensitivity to eyes and eye cues (Kano & Tomonaga, Reference Kano and Tomonaga2010; Tomasello, Hare, Lehmann, & Call, Reference Tomasello, Hare, Lehmann and Call2007). This human-specific sensitivity to eyes manifests itself by a more effective and broadened use of eye cues to detect attentional, emotional, and mental-state cues in others. This sensitivity relies upon the unique morphology of the human eyes characterized by their horizontally elongated form and exposed white sclera. Critically, neuroscience research indicates that this sensitivity to eyes is underpinned by a network of brain regions comprising the amygdala at the subcortical level and posterior superior temporal and medial prefrontal cortices at the cortical level, implicated in enhanced attention to eyes and the detection of attentional, emotional, and mental states from eye cues, respectively (Schilbach et al., Reference Schilbach, Timmermans, Reddy, Costall, Bente, Schlicht and Vogeley2013). Developmental research with infants points to the existence of increased attention to eyes in newborns and indicates that the processes involved in detecting attentional, emotional, and mental states from eyes emerge during the course of the first year of life (Grossmann, Reference Grossmann2017). Based on an integration of these findings, the theoretical argument has been advanced that eyes provide a basis for connecting with other minds (Grossmann, Reference Grossmann2017). In other words, processes related to privileged orientation and attention to the eyes may help with detecting the presence of other minds, and processes related to decoding information contained in the eye or eye region helps with tracking the contents of other minds, including others' knowledge states.
Second, the existing developmental cognitive neuroscience research with infants, which has not been discussed by Phillips et al. shows that the brain processes underpinning our ability to read other minds develop early in infancy. This is in line with mounting evidence from numerous behavioral studies attesting to infants' mind reading abilities and underlines that behavioral and neuroscience research converges on the notion that access to other minds is an important and early emerging feature of human social cognition. Moreover, the neuroimaging research demonstrates similarity in the brain processes engaged by human infants and adults when processing eye cues (Grossmann, Reference Grossmann2017). Based on this similarity, it seems unlikely that different mechanisms (representations) are at play in adults than in infants, further supporting the notion of the early developmental emergence of knowledge attribution. Yet the kind of mental-state understanding attributed to infants based on these neuroscience and behavioral findings does not require the infant to have an explicit (conceptual) grasp of other minds. Indeed, evidence is accumulating that eye-based social cognition might be rooted in automatic processes as demonstrated by neuroscientific research on subliminal face and gaze processing with human infants (Jessen & Grossmann, Reference Jessen and Grossmann2014, Reference Jessen and Grossmann2020).
Third, although the emphasis here was on the ontogenetic and brain origins of human-specific sensitive responding to eyes, eyes are certainly not the only route to understanding other minds. As pointed out by Phillips et al., other sources are also important for informing us about the presence and contents of other minds. For example, there is much research to show that humans use vocal cues in a very similar manner as they use facial and eye cues and sensitivity to voices emerges early in ontogeny (Grossmann, Oberecker, Koch, & Friederici, Reference Grossmann, Oberecker, Koch and Friederici2010). Furthermore, in certain contexts, vocal cues have been shown to provide more powerful information regarding another person's mind than facial cues (Schroeder & Epley, Reference Schroeder and Epley2015). Apart from vocal cues, humans may also rely on information provided through touch (Fairhurst, Löken, & Grossmann, Reference Fairhurst, Löken and Grossmann2014), although when compared to facial and vocal cues, touch as a means for gleaning insights into other minds has been relatively neglected.
From an evolutionary perspective, eye cues are considered to function particularly well during close range interactions without direct physical contact, which are characteristic for many collaborative activities in humans (Tomasello, Melis, Tennie, Wyman, & Herrmann, Reference Tomasello, Melis, Tennie, Wyman and Herrmann2012). This includes activities such as hunting and gathering (foraging), which is considered the primary and ancestral form of subsistence within the genus Homo. Compared to vocal signaling, coordination through eye cues has the advantage that it can occur silently, making it an ideal form of communication between cooperators during group activities such as gathering and hunting, when at the risk of being noticed by predators or prey. Despite the adaptive advantages with respect to human cooperative activities seen in adults, from a developmental perspective, an early emerging sensitivity to eyes might lay the foundation for being able to identify, choose between, and coordinate with cooperative partners.
In summary, we advocate for an approach that systematically and more mechanistically assesses the origins of knowledge about others by taking a developmental cognitive neuroscience perspective in order to advance a more complete understanding of how humans come to understand other minds.
Financial support
T.G. was partly funded by the National Science Foundation #2017229.
Conflict of interest
None.