Do we represent intentional action as recursively embedded? The answer must be empirical. A comment on Vicari and Adenzato (2014)
Introduction
In 1951, Lashley published a justly famous exposition of an idea that has been repeated and refined in much subsequent research: that there is some fundamental cognitive link between the structure of complex motor plans, and the structures of linguistic syntax (Lashley, 1951). Particularly since the discovery of mirror neurons (Rizzolatti, Fadiga, Gallese, & Fogassi, 1996), this notion has entered the mainstream of thought in cognitive science. However, there is considerable variation among researchers about what the specific relevant parallels are (compare, for example, (Rizzolatti & Arbib, 1998) and (Pulvermüller, 2010)) along with considerable skepticism about whether these links are deep and interesting (Anscombe, 1957, Anscombe, 1965, Moro, 2014, Toni et al., 2008). Elsewhere, we have offered our own perspective on this question, hearkening back to Lashley’s ideas that hierarchical organization is the key shared characteristic between action, music and language (Fitch & Martins, 2014).
In a recent manuscript published in this journal, Vicari and Adenzato (Vicari & Adenzato, 2014), henceforth VA, analyze the plausibility of Hauser, Chomsky and Fitch’s (henceforth HCF) hypothesis (Hauser, Chomsky, & Fitch, 2002) that recursion is either domain-specific to language, or that recursion’s uses in other domains are parasitic upon linguistic recursion. VA aim to falsify this hypothesis by first identifying “the formal features of recursion” in intentional action, a non-linguistic domain, and then by showing that this domain is not grounded on language. For the latter argument they review data purportedly showing that “linguistic recursion might be embodied in motor processing”, and that in some situations “linguistic and motor-intentional recursions might be double dissociated”.
This is an interesting and plausible argument, and we certainly are sympathetic with VA’s efforts to review and address the theoretical and methodological difficulties involved in investigating recursion. Although we agree that there are reasons to doubt HCF’s hypothesis, especially considering recent empirical research concerning recursion in vision (Martins, 2012, Martins, Laaha et al., 2014, Martins et al., 2015, Martins, Fischmeister et al., 2014), we here argue that the argument presented by VA is inadequate on two grounds.
First, humans’ ability to represent intentional action as recursive is an assumption of VA’s model, not something that has been empirically demonstrated. Our argument is the following: although it is possible to formally represent several structures in the environment as generated by recursive rules (or as having a recursive structure), it is also quite possible that human subjects are unable to represent these structures cognitively or neurally (as formally modeled by VA). This would obviously make VA’s formalism an unrealistic model of human cognition, and nullify the biological and evolutionary implications VA draw from it. A specific set of empirical studies would need to be successfully carried out to evaluate the accuracy of VA’s assumptions, as we detail below. Clearly, we cannot use untested cognitive models to support claims about the properties and evolution of human cognition, unless there is empirical evidence supporting such models as a good approximation of what people actually do. This problem is certainly not limited to recursion, and occurs whenever distinct modeling strategies exist to adequately explain identical phenomenon, as is often the case in the field of language evolution (Baronchelli et al., 2012, Chomsky, 2010, Christiansen and Kirby, 2003, Griffiths and Kalish, 2007, Griffiths et al., 2008, Kirby, 2001, Kirby et al., 2008, McCrohon, 2012, Niyogi and Berwick, 1997, Nowak et al., 2001).
The second flaw in VA’s argument is their logical slip of taking the part for the whole, i.e., taking human intentional motor action as having the same identity and properties as all motor action. This becomes clear in VA’s review of data on the neural bases of the motor system, taken as evidence that “linguistic recursion might be embodied in motor processing” (and hence in recursive intentional action). Clearly, even if we agree that some actions are intentional and recursive, it does not follow that all motor action is intentional and recursive. This is a particular problem when analyzing the properties of parts of the motor system with clear homologs in other mammals (e.g. the basal ganglia), and then using these to draw evolutionary conclusions about the primacy of motor recursion over language recursion.
It seems clear that pure theoretical analyses cannot replace empirical data in assessing the architecture of human cognition or in drawing further evolutionary conclusions. Indeed, such analyses can be evaluated empirically, but it is hard work. For instance, in a series of recent studies, we have tested for the existence of recursive cognitive abilities in the visuo-spatial domain. We have found that both human adults and children (Martins, 2012, Martins, Laaha et al., 2014) can represent visual recursion (operationalized as self-embedded hierarchical structure). This ability is neither affected by verbal interference (Martins et al., 2015) nor does it activate language brain areas (Martins, Fischmeister et al., 2014). These data provide an empirical falsification of the HCF hypothesis much more convincingly than previous arguments assuming that visual perception is recursive and independent of language (Jackendoff & Pinker, 2005).
Below, we will describe VA’s article in further detail and demonstrate that there are alternative approaches to modeling motor processing. We argue that, despite the large number of cognitive domains in which recursion has been claimed to exist, from language to music to social intelligence to architecture, there are typically non-recursive alternative explanations for hierarchy in these domains, and that existing proposals do not successfully address the core issue of recursion in language and its relation (or lack thereof) to other domains of thought. Our central argument is that, by taking a plausible characterization of certain specific aspects of human intentionality as given, and then extending this characterization to motor planning in general (including motor behavior in nonhuman animals), VA greatly overstate their argument that action recursion is an evolutionary precursor of linguistic (or other cognitive) recursion. Indeed, we give several reasons to seriously doubt the existence of recursive representations in animal motor planning, even in intentional actions. We conclude that VA’s argument, while interesting, lacks the empirical support required to make it plausible.
Section snippets
Vicari and Adenzato’s argument
VA’s reading of HCF leads them to specify four properties which are necessary and sufficient for recursion: self-embedding, long-distance dependency, identity preservation and discrete infinity. They conclude that the logical structure of intentional action satisfies all four conditions.
First, VA rely upon Searle’s (Searle, 1983) analysis of intentional action, concluding from this that the structure of intentional action is self-referential. According to this analysis the content of an
Is self-embedding a basic feature of motor control?
Consider a cat whose goal (intention, in the ordinary sense) is to catch a mouse, and whose motor actions to this effect can be said to be “intentional” (in the philosopher’s sense of “aboutness”) with respect to mouse-catching. The cat wants the mouse, and cognitively represents this desire. Now it may be that, in a misguided attempt at escape, the mouse runs into the cat’s claws and is captured and eaten. By Searle’s analysis, we must conclude that the cat’s intentional goal was not satisfied
Conclusion
In sum, VA do not, in our opinion, demonstrate recursion outside of language. Rather they build a theoretical model that assumes recursion in intentional action, and use this as a basis for a wider analysis doubting the primacy of recursion for language. While we find this analysis interesting, it remain unconvincing. If their claims about the recursive structure of intentional action remain unchallenged, and empirically unverified, they are more likely to generate confusion rather than clarity.
References (52)
Cognitive control, hierarchy, and the rostro–caudal organization of the frontal lobes
Trends in Cognitive Sciences
(2008)- et al.
Language evolution: Consensus and controversies
Trends in Cognitive Sciences
(2003) - et al.
The evolution of the language faculty: Clarifications and implications
Cognition
(2005) - et al.
The capacity for music: What is it, and what’s special about it?
Cognition
(2006) - et al.
The nature of the language faculty and its implications for evolution of language (reply to fitch, Hauser, and Chomsky)
Cognition
(2005) - et al.
How children perceive fractals: Hierarchical self-similarity and cognitive development
Cognition
(2014) - et al.
Representing visual recursion does not require verbal or motor resources
Cognitive Psychology
(2015) On the similarity between syntax and actions
Trends in Cognitive Sciences
(2014)Brain embodiment of syntax and grammar: Discrete combinatorial mechanisms spelt out in neuronal circuits
Brain and Language
(2010)- et al.
Language within our grasp
Trends in Neuroscience
(1998)
Premotor cortex and the recognition of motor actions
Cognitive Brain Research
Recursion in phonology
Lingua
The evolution of language from social cognition
Current Opinion in Neurobiology
On dendrophilia. Comment on “toward a computational framework for cognitive biology: Unifying approaches from cognitive neuroscience and comparative cognition by W. Tecumseh Fitch”
Physics of Life Reviews
Language beyond action
Journal of Physiology-Paris
Is recursion language-specific? Evidence of recursive mechanisms in the structure of intentional action
Consciousness and Cognition
Intention
The intentionality of sensation: A grammatical feature
Meaning, reference, and intentionality in the natural vocalizations of monkeys
Why monkeys don’t have language
Some simple evo devo theses: How true might they be for language?
Bamana sand divination: Recursion in ethnomathematics
American Anthropologist
Fractals in african settlement architecture
Complexity
Recursion—or, better computational thinking through laughter
International Journal of Computers for Mathematical Learning
Hierarchical processing in music, language, and action: Lashley revisited
Annals of the New York Academy of Sciences
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The never-ending recursion
2017, Journal of Applied LogicCitation Excerpt :Since the very insightful paper published by [33], a variety of studies have been carried out regarding the notion of recursion. This variety not only concerns the domain of language, as this notion has also been analyzed within the (cognitive) domain of music (see [41,35,60], among others), and Comparative Psychology (see [25,27,56,21]), but as Martins and Fitch [47] have suggested, recursion plays also a crucial role in visuo-spatial processing (see [46,45,50]), phonology (see for instance [69]), or intentional action [71], among other domains. The current paper does not focus specifically on one domain or another among those mentioned above; rather, it analyzes two different approaches to recursion.
Self-similarity and recursion as default modes in human cognition
2017, CortexCitation Excerpt :All subjects gave informed written consent prior to participation in the study, which was approved by the appropriate ethics committee of the Medical University of Vienna. The task used in this functional Magnetic Resonance Imaging (fMRI) experiment has been described in detail elsewhere (cf. Martins & Fitch, 2015; Martins, Laaha, et al., 2014) and consisted of fMRI compatible adaptations of the Visual Recursion Task (VRT) and Embedded Iteration Task (EIT) (Martins, 2012). Both tasks are forced-choice procedures using identical target stimuli (see Fig. 4A and B iteration four).
The ontogenesis of action syntax
2019, Collabra: PsychologyThe Cognitive Architecture of Recursion: Behavioral and fMRI Evidence from the Visual, Musical and Motor Domains
2017, CogSci 2017 - Proceedings of the 39th Annual Meeting of the Cognitive Science Society: Computational Foundations of Cognition
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Address: Department of Cognitive Biology, Althanstrasse 14, 1090 Vienna, Austria.