Context, cognition and communication in language

Questions pertaining to the unique structure and organisation of language have a long history in the field of linguistics. In recent years, researchers have explored cultural evolutionary explanations, showing how language structure emerges from weak biases amplified over repeated patterns of learning and use. One outstanding issue in these frameworks is accounting for the role of context. In particular, many linguistic phenomena are said to to be context-dependent; interpretation does not take place in a void, and requires enrichment from the current state of the conversation, the physical situation, and common knowledge about the world. Modelling the relationship between language structure and context is therefore crucial for developing a cultural evolutionary approach to language. One approach is to use statistical analyses to investigate large-scale, cross-cultural datasets. However, due to the inherent limitations of statistical analyses, especially with regards to the inadequacy of these methods to test hypotheses about causal relationships, I argue that experiments are better suited to address questions pertaining to language structure and context. From here, I present a series of artificial language experiments, with the central aim being to test how manipulations to context influence the structure and organisation of language. Experiment 1 builds upon previous work in iterated learning and communication games through demonstrating that the emergence of optimal communication systems is contingent on the contexts in which languages are learned and used. The results show that language systems gradually evolve to only encode information that is informative for conveying the intended meaning of the speaker - resulting in markedly different systems of communication. Whereas Experiment 1 focused on how context influences the emergence of structure, Experiments 2 and 3 investigate under what circumstances do manipulations to context result in the loss of structure. While the results are inconclusive across these two experiments, there is tentative evidence that manipulations to context can disrupt structure, but only when interacting with other factors. Lastly, Experiment 4 investigates whether the degree of signal autonomy (the capacity for a signal to be interpreted without recourse to contextual information) is shaped by manipulations to contextual predictability: the extent to which a speaker can estimate and exploit contextual information a hearer uses in interpreting an utterance. When the context is predictable, speakers organise languages to be less autonomous (more context-dependent) through combining linguistic signals with contextual information to reduce effort in production and minimise uncertainty in comprehension. By decreasing contextual predictability, speakers increasingly rely on strategies that promote more autonomous signals, as these signals depend less on contextual information to discriminate between possible meanings. Overall, these experiments provide proof-of-concept for investigating the relationship between language structure and context, showing that the organisational principles underpinning language are the result of competing pressures from context, cognition, and communication

Using a Tri-Isotope (13C, 15N, 33P) Labelling Method to Quantify Rhizodeposition

Belowground (BG) plant resource allocation, including roots and rhizodeposition, is a major source of soil organic matter. Knowledge on the amounts and turnover of BG carbon (C), nitrogen (N), and phosphorus (P) in soil is critical to the understanding of how these elements cycle in soil-plant system. However, the assumptions underlying the quantification and tracking of rhizodeposition using isotope labeling methods have hardly been tested. The main objectives of this chapter were to (i) review the different plant labeling techniques for each of the three elements; (ii) describe a novel method for the simultaneous investigation of C, N, and P rhizodeposition in sand; and (iii) test the methodological assumptions underlying quantification of rhizodeposition. Stable 13C and 15N isotopes were widely used to study rhizodeposition of plants either separately or in combination, while P radioisotopes (32P, 33P) were used to investigate root distribution. The combination of the 13CO2 single-pulse labeling with the simultaneous 15N and 33P cotton-wick stem feeding effectively labeled Canavalia brasiliensis roots and facilitated the estimation of rhizodeposited C, N, and P input from root systems. However, the isotope distribution was uneven within the root system for all three elements. Additionally, we observed a progressive translocation from shoot to roots for 15N and 33P over 15 days after labeling, while the 13C tracer was diluted with newly assimilated non-enriched C compounds over time. Younger root sections also showed higher specific activities (33P/31P) than the older ones. The relatively high 33P radioactivity recovered in sand right away at the first sampling was attributed to an artifact generated by the stem feeding labeling method. Overall, our results suggest that the assumptions underlying the use of isotope methods for studying rhizodeposition are violated, which will affect the extent of quantification of rhizodeposition. The consequences of nonhomogeneous labeling of root segments of different age require further investigation. The use of a time-integrated isotopic composition of the root is recommended to not only account for temporal variation of isotopes but also to improve the method of quantifying plant rhizodeposition