Eliminating unpredictable variation through iterated learning

Human languages may be shaped not only by the (individual psychological) processes of language acquisition, but also by population-level processes arising from repeated language learning and use. One prevalent feature of natural languages is that they avoid unpredictable variation. The current work explores whether linguistic predictability might result from a process of iterated learning in simple diffusion chains of adults. An iterated artificial language learning methodology was used, in which participants were organised into diffusion chains: the first individual in each chain was exposed to an artificial language which exhibited unpredictability in plural marking, and subsequent learners were exposed to the language produced by the previous learner in their chain. Diffusion chains, but not isolate learners, were found to cumulatively increase predictability of plural marking by lexicalising the choice of plural marker. This suggests that such gradual, cumulative population-level processes offer a possible explanation for regularity in language

Iron phosphate glasses: Structure determination and radiation tolerance

AbstractIron phosphate glass (IPG) has gained recent interest for use in encapsulating radioactive waste for long term storage. In this work, we investigate 5 different compositions of iron phosphate glass. We consider amorphous structures of 3 known crystalline phases: Fe2+Fe23+(P2O7)2, Fe43+(P2O7)3 and Fe3+(PO3)3, and structures of IPG (40mol% Fe2O3 and 60mol% P2O5), with 4% and 17% Fe2+ ion concentrations.Using constant volume molecular dynamics (MD), we quench a set of structures for each glass composition, to find the optimal density structure. We found that the lowest energy structures of IPG with 4% and 17% concentration of Fe2+, have a density of 3.25 and 3.28g/cm3 respectively. This is slightly higher than the experimentally measured values of 2.9 and 2.95g/cm3 respectively.We also estimate an upper and lower bound on the melting temperatures of each glass, then for each glass, we simulate radiation damage cascades at 4keV. The cascade structures can be in the form of either a concentrated thermal spike or more diffuse with sub-cascade branching. We found that the glass compositions with a higher Fe/P atomic ratio, contained a greater number of displacements after the cascade. We also found that the IPG with 4% Fe2+, contained slightly fewer displacements than the IPG with 17% Fe2+. This is consistent with our previous work, which showed that the threshold displacement energies are lower for glasses with a lower Fe2+ content. In all the simulations, many PO4 polyhedra are destroyed during the early stages of irradiation, but recover strongly over a time scale of picoseconds, leaving very few over or under co-ordinated P atoms at the end of the ballistic phase. This is in contrast to recent work in apatite. The strong recovery indicates that phosphate glasses with a low Fe2+ content could be good materials for waste encapsulation

Speakers align with their partner's overspecification during interaction

Speakers often overspecify by encoding more information than is necessary when referring to an object (e.g., “the blue mug” for the only mug in a group of objects). We investigated the role of a partner's linguistic behavior (whether or not they overspecify) on a speaker's own tendency to overspecify. We used a director–matcher task in which speakers interacted with a partner who either consistently overspecified or minimally specified in the color/size dimension (Experiments 1, 2, and 3), as well as with a partner who switched behaviors midway through interaction (Experiments 4 and 5). We found that speakers aligned with their partner's linguistic behavior to produce overspecific or minimally specific descriptions, and we saw little evidence that the alignment was enhanced by lexical or semantic repetition across prime and target trials. Time-course analyses showed that alignment increased over the course of the interaction, and speakers appeared to track a change in the partner's linguistic behavior, altering their reference strategy to continue matching that of their partner's. These results demonstrate the persistent influence of a partner's behavior on speakers across the duration of an interaction

Are you thinking what I’m thinking?:Perspective-taking in a language game

Many theories of communication claim that perspective-taking is a fundamental component of the successful design of utterances for a specific audience. In three experiments, we investigated perspective-taking in a constrained communication situation: Participants played a word guessing game where each trial required them to select a clue word to communicate a single target word to their partner. In many cases, the task requires participants to take the perspective of their partner when generating, evaluating, and selecting potential clue words. For example, if the target word was ‘heart’, the first word that came to mind might be ‘love’, but this would not in fact be a very useful clue word. Instead, a word like ‘cardiovascular’ is much more likely than ‘love’ to make the partner guess ‘heart’. Pairs of participants took turns giving and receiving clues to guess target words, receiving feedback after each trial. In Experiment 1, participants appeared unable to improve their perspective-taking over repeated interactions, despite a baseline performance that suggested strong perspective-taking abilities. In Experiment 2, which included extensive feedback after each trial and only target words for which good clues existed and which required perspective-taking, some measures of perspective-taking showed modest improvements. In Experiment 3, which was conducted online, we used Experiment 2 feedback with Experiment 1 target words. As in Experiment 1, participants did not improve over the course of the game in Experiment 3. The results of these three experiments show quite strong limits on people’s ability to adapt and improve perspective-taking without the context provided by interaction history and growing common ground

An experimental study of semantic extension in a novel communication system

Semantic extension plays a key role in language change and grammaticalisation. Here we use a dyadic interaction paradigm to study semantic extension of novel labels in controlled circumstances. We ask whether participants will be able to (i) use highly accessible associations in the perceptual environment (colour-shape associations) to converge on a meaning for the novel labels, and (ii) extend these meanings to apply to both concrete targets (objects) and abstract targets (emotions). Further, given the argument that both metonymy and metaphor are important drivers of language change, we investigate whether participants will be able to draw on relations of contiguity (‘metonymic’ associations, e.g. colour-shape or object-colour) and relations of similarity (‘metaphorical’ associations, e.g. emotion-colour) to extend the meaning of labels

The spontaneous formation of stereotypes via cumulative cultural evolution

All people share knowledge of cultural stereotypes of social groups—but what are the origins of these stereotypes? We examined whether stereotypes form spontaneously as information is repeatedly passed from person to person. As information about novel social targets was passed down a chain of individuals, what initially began as a set of random associations evolved into a system that was simplified and categorically structured. Over time, novel stereotypes emerged that not only were increasingly learnable but also allowed generalizations to be made about previously unseen social targets. By illuminating how cognitive and social factors influence how stereotypes form and change, these findings show how stereotypes might naturally evolve or be manipulated

Improved Limits on Sterile Neutrino Dark Matter using Full-Sky Fermi Gamma-Ray Burst Monitor Data

A sterile neutrino of ~keV mass is a well motivated dark matter candidate. Its decay generates an X-ray line that offers a unique target for X-ray telescopes. For the first time, we use the Gamma-ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope to search for sterile neutrino decay lines; our analysis covers the energy range 10-25 keV (sterile neutrino mass 20-50 keV), which is inaccessible to X-ray and gamma-ray satellites such as Chandra, Suzaku, XMM-Newton, and INTEGRAL. The extremely wide field of view of the GBM enables a large fraction of the Milky Way dark matter halo to be probed. After implementing careful data cuts, we obtain ~53 days of full sky observational data. We observe an excess of photons towards the Galactic Center, as expected from astrophysical emission. We search for sterile neutrino decay lines in the energy spectrum, and find no significant signal. From this, we obtain upper limits on the sterile neutrino mixing angle as a function of mass. In the sterile neutrino mass range 25-40 keV, we improve upon previous upper limits by approximately an order of magnitude. Better understanding of detector and astrophysical backgrounds, as well as detector response, will further improve the sensitivity of a search with the GBM.Comment: 16 pages, 11 figures, references added, discussion expanded, some typos fixed, matches the published versio