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2. Iterated Learning Model (ILM)
2.1 Theory of Iterated Learning
As the key mechanism of the cultural evolution of language, the aforementioned models are largely based on iterated learning.
Iterated learning refers to the process by which an individual acquires a behavior by observing a similar behavior in another individual who acquired it in the same way.
Early studies of iterated learning that observed human behaviour in a laboratory setting were designed to learn about cultural transmission. One of the pioneer studies in iterated learning is Bartlett’s (1937) ‘serial reproduction’ experiment, in which participants were exposed to some stimulus (such as drawings) and were then asked to reproduce the same material from memory. Their reproduced work served as the stimulus for a second participant, and so on. Bartlett observed that the material that was transmitted in this manner had changed as participants impressed their expectations about what they deemed was the right and appropriate content onto the material, thus causing it to be restructured. For example, if one was shown a picture of an apple and told to draw it, another would observe the resultant drawing and produce a new drawing of an apple (as pictured below). An interesting observation that came out of the study was that drawings could change toward conventional, prototypical forms of the object drawn. (Bartlett, 1932)
Spoken and signed languages, birdsong, and music are transmitted via iterated learning as opposed to explicit teaching. One’s linguistic behavior is thus a product of one’s observation of others’ similar behavior, which was induced by that of those who came before. The chain of diffusion occurs in not only cultural transmission, but also horizontal negotiation of conventions between peers of the same generation. Iterated learning is thus manifested both along a cross-generational chain of different individuals and back-and-forth within a dyad.
Iterated learning can have profound effects on linguistic structure. A study on such effects involved the learning of an artificial language by participants who were organized into diffusion chains. Such studies show that iterated is an adaptive process, in which the linguistic behavior being transmitted gains input from each generation to overcome key constraints. Some constraints to a language’s transmission over time include error rate and ambiguity.
2.2 Simulating cultural transmission of language
The question of how language emerged concerns itself with both the biological evolution of the various cognitive capacities deemed necessary for language and the cultural evolution of languages, beginning from theorized proto-languages. It should be noted that cultural evolution should not be considered in isolation from its biological counterpart, as the cognitive adaptations an individual is equipped with bear implications for social interaction and learning.
Upon establishment, a language requires to be learned by subsequent generations, each from a prior generation, in a cross-generational manner, also known as vertical cultural transmission.
People learn a language from other people who once learned that language themselves.
Studies on cultural transmission seek to explain the changes an emergent language system undergoes.
The cultural transmission of a language can be said to give rise to design without intention and designer.
Exposure to linguistic behavior exhibited by members of one’s speech community induces one’s production of particular language properties. The resulting language used by one in turn translates to observable linguistic behavior which shapes the language of further members. Cultural evolution of the language is thus enabled by this cycle of repeated induction and elicitation of linguistic behavior.
Simulations of cultural transmission are based on the belief that when language is culturally transmitted, it develops:
- Structure
- Key design features unique to language over other communication systems
- Enhanced learnability through minimization of errors
The models of reserach include computational agent-based simulations, mathematical models, and most recently, laboratory experiments.
Pioneer work on agent-based simulations sought to explain how negotiation due to learners’ biases and interaction between them influence communication systems greatly. Subsequent studies focused largely on the development of linguistic structure as a byproduct of cultural learning (specifically iterated learning), despite poverty of the stimulus. Work on mathematical models followed, supplementing the findings of such agent-based simulations through mathematical characterizations of changes effected by cultural transmission.
To support prior computational and mathematical models empirically, laboratory experiments aim to demonstrate how cumulative, adaptive, and non-intentional the cultural evolution of language is, by using human participants.
2.2.1 Challenges
One significant challenge faced by studies on cultural evolution remains to be the arguably reductionist approach taken. Any given language is constituted by thousands of language systems (capturing pragmatic, semantic, morphological, and phonological distinctions) and language strategies, of which all are intertwined. No model can hope to closely replicate all aspects of language evolution through simulation.
Despite availability of real-life observations of cultural transmission with the likes of Nicaraguan Sign Language, study of genuine emergence remains limited by the lack of direct, natural, data. Hence, only indirect evidence can be drawn.
2.3 Laboratory experiments with human subjects
A couple of studies have combined iterated learning techniques with artificial language learning or communication game paradigms in a bid to explore how languages and other communication systems evolve through learning and use. In language evolution, iterated learning has become a paradigm which involves experimentation with artificial languages. Human participants learn a set of items in the language, and then produce linguistic behavior which subsequent individuals learn from and so on. This was introduced by researchers Kirby S, Cornish H, and Smith K. A learning bottleneck is also imposed on transmission: participants are asked to learn a target language based on exposure to a smaller set of language items from the original set of stimuli, with the language produced by the nth participant. In this chain, the nth participant provides the input to participant n +1 and so forth. In short, participants have access to only a limited set of data.
2.3.1 Literature on laboratory experiments with humans
Many types of experiments relating to exploring the phenomenon of language evolution have been conducted in the laboratory. They are divided into experiments focusing on signal creation, the emergence of communication systems, and cultural transmission itself.
Signal Creation
Understanding the origins of language will involve the uncovering of the necessary cognitive capacities used for linguistic communication and detecting communication intentions. Studies on signal creation investigate how individuals recognise the communicative nature of certain behaviour, before even questioning how meaning is created from the signals. Scott-Phillips et al. (2009) ‘s embodied communication game (ECG) is a two-player game designed to serve this investigation. It requires participants to travel around a 2X2 grid with movement as their only communicative resource. This forces participants to find ways in revealing which movements are communicative in nature rather than acts of travel. The difficulty of this task revealed that common ground serves is especially key to the emergence of communication channels. Related work (as cited in Scott-Phillips & Kirby, 2010) also lead to similar conclusions. The challenge of these games is highlighted in the difficulty of communicating one’s communicative intent.
Emergence of communication systems
Once communicative intent is established, individuals now face the task of negotiating the forms and meanings of symbols to create a communication system. In a pioneer study done by Galantucci (2005), pairs of participants were tasked to invent and agree on a set of signs to use to solve a coordination problem. The study aimed to illustrate how human communication can be understood as a form of joint action. An example of a line of research that has been spawned from the pioneering studies on the role of interaction in the emergence of communication system is the use of graphical communication tasks. Such tasks are advantageous in its provision of a medium which allows the invention of new signs to be used in an interactive context. Examples of studies that illustrates this include those done by Garrod et al (2007, 2010).
Cultural transmission
Following the establishment of some sort of language, cultural transmission, which is an instance of iterated learning, takes place. In Kirby et al’s (2008) experiment, participants were asked to learn labels for coloured moving shapes, where the initial artificial language provided a randomly generated, unique label for the shapes. Their findings revealed a structured language that developed from the initial unstructured set of meaning-signal associations as a result of the iterated learning. By the 10th participant, each label had consisted of a prefix which specified colour (e.g. ne– for black, la– for blue), a stem for shape (e.g. –ho– for circle, -ki- for triangle) and an affix specifying motion (e.g. –plo for bouncing, –pilu for looping). As predicted by mathematical modelling results, languages developed over time to ones that facilitated generalisations and rules. Compositional languages also developed where components or sub-parts of each complex label or word specified components of the picture that the label had referred to.