Keven & Akins (K&A) provide an elegant synthesis of research illuminating the developmental course and functional significance of the fetal and neonatal behavior of tongue protrusion/retraction (TP/R). This behavior is particularly interesting because newborn tongue protruding provides a large part of the evidence purporting to show that newborn human infants can imitate. Newborn imitation, in turn, is particularly interesting because of its implications for our understanding of the origins of knowledge (Jones Reference Jones, Blumberg, Spencer and Shenk2017).
Although it is almost never mentioned by developmental psychologists, the claim that newborns can imitate is also a strong claim that we are born already possessed of a good deal of specific knowledge. In particular, it is a claim that we are born with (1) knowledge about at least some parts of our bodies, including how to find them, the movements each can make, and how to make those movements; (2) the same knowledge, but represented differently (e.g., in vision versus in proprioception), about the body parts and movements of others; and (3) knowledge about how the different representations of the two sets of body parts and movements map to each other. These kinds of knowledge appear to be irreducible requirements for the imitation of even the simplest actions. How could they develop before birth? Although it is conceivable that some limited representations of infants' own parts and actions might be constructed by their prenatal movements, infants in the womb can have no experience of the visual information produced by the bodies and actions of others. Therefore, the claim that newborns imitate is a claim that we inherit specific knowledge – and complex, multidimensional knowledge at that.
This claim is extraordinary. It is, therefore, surprising that newborn imitation has been so widely, calmly, and uncritically accepted for almost four decades among developmental researchers, and so highly influential in theory building, research, and teaching across a range of disciplines. Throughout this period, new data purporting to show neonates imitating new behaviors have continued to appear. However, there has been little progress in the development of an adequate, empirically supported explanation of where this very early competency might come from and how it might work. The two dominant theoretical proposals identified by K&A – the active intermodal matching (AIM) model (Meltzoff & Moore Reference Meltzoff and Moore1997) and the mirror neuron account (e.g., Simpson et al. Reference Simpson, Paukner, Suomi, Ferrari, Ferrari and Rizzolatti2015) are both very sparse and difficult to test. AIM names a set of separate, necessary components of an ability to imitate, along with the proposed links among them. However, the theory provides no description of the possible mechanisms behind the labels. This theory, then, is not testable in its current form. The mirror neuron explanation of newborn imitation is a relatively recent proposal that by itself is not a complete theory of imitation, and which is not directly testable in human infants. Consequently, the evidence for both theories is still largely confined to repeated demonstrations of newborn behavioral matching.
Although those arguing for the reality of newborn imitation cite neonates' matching of several simple actions (e.g., Meltzoff Reference Meltzoff2005), independent reviews (e.g., Anisfeld Reference Anisfeld1996; Ray & Heyes Reference Ray and Heyes2011) have concluded that only infant tongue movements are reliably increased in the presence of a model of the behavior. A number of studies have shown that newborns similarly increase their tongue movements as they experience a range of stimuli, including other modeled behaviors (Oostenbroek et al. Reference Oostenbroek, Suddendorf, Nielsen, Redshaw, Kennedy-Costantini, Davis, Clark and Slaughter2016) and visual, auditory, and somatosensory stimuli bearing no resemblance to a tongue protruding model (Jones Reference Jones2009). These data suggest that tongue movements are a general arousal response in neonates. The target article supplies a convincing explanation of why tongue protrusions in particular are associated with moderate increases in arousal. What will the research community make of this?
The arousal explanation of babies' behavior in imitation experiments has met with considerable resistance. There is a danger that the contribution of the present article to our understanding of infant behavior – and, importantly, of what that behavior does or does not tell us about the origins of knowledge – will also be dismissed, because its authors have not directly shown that newborn infants do not imitate tongue protruding/retraction.
We should remind ourselves, then, that given two incompatible explanations of the same phenomenon, we are obliged by the scientific convention of Occam's razor to favor the simplest, testable explanation – that is, the explanation that accounts for the most data using the fewest unsupported assumptions. In the case of newborn infants' response to modeled tongue protrusions, the simplest explanation with the fewest unsupported assumptions is not that newborn babies have inherited the specific knowledge of their own and others' bodies and how each maps to the other that imitation would require. There is no evidence that newborns possess any such knowledge – or for that matter, that they possess an active intermodal matching mechanism, or functional mirror neurons. The simplest explanation for newborns' increasing their tongue movements in the presence of a tongue-protruding model is that the model's behavior is visually interesting and so moderately arousing; that tongue movements – which sometimes take the tongue beyond the infant's lips – are components of newborn suckling, and as such are readily activated with increases in arousal; and that the match between the display that arouses the infant and the infant's arousal response is coincidental. This account is supported by evidence that tongue movements are an arousal response, and now by K&A's documentation of the fetal development of tongue protruding/retraction, which explains the functional place of TP/R in the newborn's repertoire, and why TP/R is easily activated by generalized arousal.
The claim that newborns can imitate is not equally well explained or supported. It is nevertheless woven into the fabric of theories in a range of disciplines beyond developmental science. Those constructing such theories trust that developmentalists have done the work necessary to establish that newborn imitation is real. We have not. It may be time to apply general scientific standards of evidence and acknowledge the likelihood that newborns do not imitate.
Keven & Akins (K&A) provide an elegant synthesis of research illuminating the developmental course and functional significance of the fetal and neonatal behavior of tongue protrusion/retraction (TP/R). This behavior is particularly interesting because newborn tongue protruding provides a large part of the evidence purporting to show that newborn human infants can imitate. Newborn imitation, in turn, is particularly interesting because of its implications for our understanding of the origins of knowledge (Jones Reference Jones, Blumberg, Spencer and Shenk2017).
Although it is almost never mentioned by developmental psychologists, the claim that newborns can imitate is also a strong claim that we are born already possessed of a good deal of specific knowledge. In particular, it is a claim that we are born with (1) knowledge about at least some parts of our bodies, including how to find them, the movements each can make, and how to make those movements; (2) the same knowledge, but represented differently (e.g., in vision versus in proprioception), about the body parts and movements of others; and (3) knowledge about how the different representations of the two sets of body parts and movements map to each other. These kinds of knowledge appear to be irreducible requirements for the imitation of even the simplest actions. How could they develop before birth? Although it is conceivable that some limited representations of infants' own parts and actions might be constructed by their prenatal movements, infants in the womb can have no experience of the visual information produced by the bodies and actions of others. Therefore, the claim that newborns imitate is a claim that we inherit specific knowledge – and complex, multidimensional knowledge at that.
This claim is extraordinary. It is, therefore, surprising that newborn imitation has been so widely, calmly, and uncritically accepted for almost four decades among developmental researchers, and so highly influential in theory building, research, and teaching across a range of disciplines. Throughout this period, new data purporting to show neonates imitating new behaviors have continued to appear. However, there has been little progress in the development of an adequate, empirically supported explanation of where this very early competency might come from and how it might work. The two dominant theoretical proposals identified by K&A – the active intermodal matching (AIM) model (Meltzoff & Moore Reference Meltzoff and Moore1997) and the mirror neuron account (e.g., Simpson et al. Reference Simpson, Paukner, Suomi, Ferrari, Ferrari and Rizzolatti2015) are both very sparse and difficult to test. AIM names a set of separate, necessary components of an ability to imitate, along with the proposed links among them. However, the theory provides no description of the possible mechanisms behind the labels. This theory, then, is not testable in its current form. The mirror neuron explanation of newborn imitation is a relatively recent proposal that by itself is not a complete theory of imitation, and which is not directly testable in human infants. Consequently, the evidence for both theories is still largely confined to repeated demonstrations of newborn behavioral matching.
Although those arguing for the reality of newborn imitation cite neonates' matching of several simple actions (e.g., Meltzoff Reference Meltzoff2005), independent reviews (e.g., Anisfeld Reference Anisfeld1996; Ray & Heyes Reference Ray and Heyes2011) have concluded that only infant tongue movements are reliably increased in the presence of a model of the behavior. A number of studies have shown that newborns similarly increase their tongue movements as they experience a range of stimuli, including other modeled behaviors (Oostenbroek et al. Reference Oostenbroek, Suddendorf, Nielsen, Redshaw, Kennedy-Costantini, Davis, Clark and Slaughter2016) and visual, auditory, and somatosensory stimuli bearing no resemblance to a tongue protruding model (Jones Reference Jones2009). These data suggest that tongue movements are a general arousal response in neonates. The target article supplies a convincing explanation of why tongue protrusions in particular are associated with moderate increases in arousal. What will the research community make of this?
The arousal explanation of babies' behavior in imitation experiments has met with considerable resistance. There is a danger that the contribution of the present article to our understanding of infant behavior – and, importantly, of what that behavior does or does not tell us about the origins of knowledge – will also be dismissed, because its authors have not directly shown that newborn infants do not imitate tongue protruding/retraction.
We should remind ourselves, then, that given two incompatible explanations of the same phenomenon, we are obliged by the scientific convention of Occam's razor to favor the simplest, testable explanation – that is, the explanation that accounts for the most data using the fewest unsupported assumptions. In the case of newborn infants' response to modeled tongue protrusions, the simplest explanation with the fewest unsupported assumptions is not that newborn babies have inherited the specific knowledge of their own and others' bodies and how each maps to the other that imitation would require. There is no evidence that newborns possess any such knowledge – or for that matter, that they possess an active intermodal matching mechanism, or functional mirror neurons. The simplest explanation for newborns' increasing their tongue movements in the presence of a tongue-protruding model is that the model's behavior is visually interesting and so moderately arousing; that tongue movements – which sometimes take the tongue beyond the infant's lips – are components of newborn suckling, and as such are readily activated with increases in arousal; and that the match between the display that arouses the infant and the infant's arousal response is coincidental. This account is supported by evidence that tongue movements are an arousal response, and now by K&A's documentation of the fetal development of tongue protruding/retraction, which explains the functional place of TP/R in the newborn's repertoire, and why TP/R is easily activated by generalized arousal.
The claim that newborns can imitate is not equally well explained or supported. It is nevertheless woven into the fabric of theories in a range of disciplines beyond developmental science. Those constructing such theories trust that developmentalists have done the work necessary to establish that newborn imitation is real. We have not. It may be time to apply general scientific standards of evidence and acknowledge the likelihood that newborns do not imitate.