A computational model of the cultural co-evolution of language and mindreading

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Co-evolution of language and mindreading: a computational exploration

Language relies on mindreading: in order to use it successfully we need to be able to entertain and recognise communicative intentions. Mindreading abilities in turn profit from language, as language provides a means for expressing mental states explicitly, and for transmitting our knowledge of mental states to others. Given this interdependence, it has been hypothesised that language and mindreading have co-evolved. In this thesis I formalise the relationship between language and mindreading in a computational model, in order to explore under what circumstances a co-evolutionary dynamic between the two skills could have gotten off the ground. In Chapter 3 I present an agent-based model which combines referential signalling with perspective-taking, where perspective-taking instantiates a very simple form of mindreading. In this model, agents’ communicative behaviour is probabilistically determined by an interplay between their language and their perspective on the world. The literal variant of these agents (explored in Chapters 3 and 4) consists of speakers who produce utterances purely based on their own language and perspective, and listeners who interpret these utterances using what they’ve learned about the speaker’s perspective through interaction. The pragmatic variant of these agents in contrast (explored in Chapters 5 and 6) consists of speakers who optimise their utterances by maximising the probability that the listener will interpret them correctly (assuming the listener shares their perspective), and listeners who interpret these utterances by reasoning about such a speaker, again using what they’ve learned about the speaker’s perspective through interaction. Learning is not straightforward however, because agents’ languages and perspectives are private (i.e. not directly observable to other agents). Instead, the Bayesian learners in this model only get to observe a speaker’s utterances in context, from which they have to simultaneously infer the speaker’s language and perspective. Simulation results show that learners can overcome this joint inference problem by bootstrapping one from the other, but that the success of this process depends on how informative the speaker’s language is. This leads to an evolutionary question: If the co-development between language-learning and perspective-learning relies on agents being exposed to an informative language, how could a population of such agents evolve an informative language from scratch? I address this question with an iterated learning version of the model described above, combined with different selection pressures. Simulation results with literal agents (presented in Chapter 4) show that an informative language emerges not just if the population is subjected to a selection pressure for communication, but also under selection for accurate perspective-inference. Under both pressures, the emergence of an informative language leads not just to more successful communication, but also to more successful perspective-inference. This is because sharing an informative language with others provides agents with information about those others’ perspectives (note that agents’ innate ability to learn about others’ perspectives does not change over generations). Simulation results with pragmatic agents (presented in Chapter 5) show the same co-evolutionary dynamics as literal agents, with the difference that they can achieve equally high levels of success at communicating and inferring perspectives with much more ambiguous languages, because they can compensate for suboptimal languages using their pragmatic ability. Finally, in Chapter 6 I explore under what circumstances such pragmatic agents could have evolved; that is, under what circumstances being a pragmatic communicator provides an evolutionary advantage over being a literal communicator. Taken together, the model results presented in this thesis suggest firstly that co-evolution between language and mindreading could have gotten off the ground under any circumstances which created a need for either improved communication or improved insight into others’ minds. Secondly, the results suggest that such a co-evolutionary dynamic could have been driven largely by cultural evolution; where mindreading improves by virtue of evolving a language

Sharedness and privateness in human early social life

This research is concerned with the innate predispositions underlying human intentional communication. Human communication is currently defined as a circular and overt attempt to modify a partner's mental states. This requires each party involved to posse ss the ability to represent and understand the other's mental states, a capability which is commonly referred to as mindreading, or theory of mind (ToM). The relevant experimental literature agrees that no such capability is to be found in the human speci es at least during the first year of life, and possibly later. This paper aims at advancing a solution to this theoretical problem. We propose to consider sharedness as the basis for intentional communication in the infant and to view it as a primitive, i nnate component of her cognitive architecture. Communication can then build upon the mental grounds that the infant takes as shared with her caregivers. We view this capability as a theory of mind in a weak sense.

Rethinking the ontogeny of mindreading

We propose a mentalistic and nativist view of human early mental and social life and of the ontogeny of mindreading. We define the mental state of sharedness as the primitive, one-sided capability to take one's own mental states as mutually known to an i nteractant. We argue that this capability is an innate feature of the human mind, which the child uses to make a subjective sense of the world and of her actions. We argue that the child takes all of her mental states as shared with her caregivers. This a llows her to interact with her caregivers in a mentalistic way from the very beginning and provides the grounds on which the later maturation of mindreading will build. As the latter process occurs, the child begins to understand the mental world in terms of differences between the mental states of different agents; subjectively, this also corresponds to the birth of privateness.

Directional adposition use in English, Swedish and Finnish

Directional adpositions such as to the left of describe where a Figure is in relation to a Ground. English and Swedish directional adpositions refer to the location of a Figure in relation to a Ground, whether both are static or in motion. In contrast, the Finnish directional adpositions edellä (in front of) and jäljessä (behind) solely describe the location of a moving Figure in relation to a moving Ground (Nikanne, 2003). When using directional adpositions, a frame of reference must be assumed for interpreting the meaning of directional adpositions. For example, the meaning of to the left of in English can be based on a relative (speaker or listener based) reference frame or an intrinsic (object based) reference frame (Levinson, 1996). When a Figure and a Ground are both in motion, it is possible for a Figure to be described as being behind or in front of the Ground, even if neither have intrinsic features. As shown by Walker (in preparation), there are good reasons to assume that in the latter case a motion based reference frame is involved. This means that if Finnish speakers would use edellä (in front of) and jäljessä (behind) more frequently in situations where both the Figure and Ground are in motion, a difference in reference frame use between Finnish on one hand and English and Swedish on the other could be expected. We asked native English, Swedish and Finnish speakers’ to select adpositions from a language specific list to describe the location of a Figure relative to a Ground when both were shown to be moving on a computer screen. We were interested in any differences between Finnish, English and Swedish speakers. All languages showed a predominant use of directional spatial adpositions referring to the lexical concepts TO THE LEFT OF, TO THE RIGHT OF, ABOVE and BELOW. There were no differences between the languages in directional adpositions use or reference frame use, including reference frame use based on motion. We conclude that despite differences in the grammars of the languages involved, and potential differences in reference frame system use, the three languages investigated encode Figure location in relation to Ground location in a similar way when both are in motion. Levinson, S. C. (1996). Frames of reference and Molyneux’s question: Crosslingiuistic evidence. In P. Bloom, M.A. Peterson, L. Nadel & M.F. Garrett (Eds.) Language and Space (pp.109-170). Massachusetts: MIT Press. Nikanne, U. (2003). How Finnish postpositions see the axis system. In E. van der Zee & J. Slack (Eds.), Representing direction in language and space. Oxford, UK: Oxford University Press. Walker, C. (in preparation). Motion encoding in language, the use of spatial locatives in a motion context. Unpublished doctoral dissertation, University of Lincoln, Lincoln. United Kingdo

Evolution, communication, and the proper function of language

Language is both a biological and a cultural phenomenon. Our aim here is to discuss, in an evolutionary perspective, the articulation of these two aspects of language. For this, we draw on the general conceptual framework developed by Ruth Millikan (1984) while at the same time dissociating ourselves from her view of language

Interpretivism and norms

This article reconsiders the relationship between interpretivism about belief and normative standards. Interpretivists have traditionally taken beliefs to be fixed in relation to norms of interpretation. However, recent work by philosophers and psychologists reveals that human belief attribution practices are governed by a rich diversity of normative standards. Interpretivists thus face a dilemma: either give up on the idea that belief is constitutively normative or countenance a context-sensitive disjunction of norms that constitute belief. Either way, interpretivists should embrace the intersubjective indeterminacy of belief