How individuals change language

Languages emerge and change over time at the population level though interactions between individual speakers. It is, however, hard to directly observe how a single speaker's linguistic innovation precipitates a population-wide change in the language, and many theoretical proposals exist. We introduce a very general mathematical model that encompasses a wide variety of individual-level linguistic behaviours and provides statistical predictions for the population-level changes that result from them. This model allows us to compare the likelihood of empirically-attested changes in definite and indefinite articles in multiple languages under different assumptions on the way in which individuals learn and use language. We find that accounts of language change that appeal primarily to errors in childhood language acquisition are very weakly supported by the historical data, whereas those that allow speakers to change incrementally across the lifespan are more plausible, particularly when combined with social network effects.

Evolutionary Linguistics

Both qualitative concepts and quantitative methods from evolutionary biology have been applied to linguistics. Many linguists have noted the similarity between biological evolution and language change, but usually have employed only selective analogies or metaphors. The development of generalized theories of evolutionary change (Dawkins and Hull) has spawned models of language change on the basis of such generalized theories. These models have led to the positing of new mechanisms of language change and new types of selection that may not have biological parallels. Quantitative methods have been applied to questions of language phylogeny in the past decade. Research has focused on widely accepted families with cognates already established by the comparative method (Indo-European, Bantu, Austronesian). Increasingly sophisticated phylogeny reconstruction models have been applied to these families to resolve questions of subgrouping, contact, and migration. Little progress has been made so far in analyzing sound correspondences in the cognates themselves.

Utterance selection model of language change

We present a mathematical formulation of a theory of language change. The theory is evolutionary in nature and has close analogies with theories of population genetics. The mathematical structure we construct similarly has correspondences with the Fisher-Wright model of population genetics, but there are significant differences. The continuous time formulation of the model is expressed in terms of a Fokker-Planck equation. This equation is exactly soluble in the case of a single speaker and can be investigated analytically in the case of multiple speakers who communicate equally with all other speakers and give their utterances equal weight. Whilst the stationary properties of this system have much in common with the single-speaker case, time-dependent properties are richer. In the particular case where linguistic forms can become extinct, we find that the presence of many speakers causes a two-stage relaxation, the first being a common marginal distribution that persists for a long time as a consequence of ultimate extinction being due to rare fluctuations.

Why is a pomegranate an apple? The role of shape, taxonomic relatedness, and prior lexical knowledge in children's overextensions of apple and dog

Children's overextensions (e.g. referring to a pomegranate as apple) raise intriguing questions regarding early word meanings. Specifically, how do object shape, taxonomic relatedness, and prior lexical knowledge influence children's overextensions? The present study sheds new light on this issue by presenting items that disentangle the three factors of shape, taxonomic category, and prior lexical knowledge, and by using a novel comprehension task (the screened-alternative task) in which children can indicate negative exemplars (e.g. which items are NOT apples). 49 subjects in three age groups participated (Ms = 2;0, 2;6, and 4;5). Findings indicate: (1) Error patterns differed by task. In production, errors were overwhelmingly due to selecting items that matched the target word in BOTH shape and taxonomic relatedness. In comprehension, more errors were based on either shape alone or taxonomic relatedness alone, and the nature and frequency of the overextensions interacted with prior lexical knowledge. (2) Error patterns also differed markedly based on the word being tested (apple vs. dog), in both comprehension and production (3) As predicted, errors were more frequent in production than comprehension, though only for children in the two younger age groups. Altogether, the study indicates that overextensions are not simply production errors, and that both taxonomic relatedness and object shape play a powerful role in early naming errors.

Mechanisms of Listeria monocytogenes-mediated modulation of tumor growth

Studies using Listeria monocytogenes as an antitumor agent were initiated to determine the requirements for Listeria-mediated tumor inhibition to occur. When Strain 13 guinea pigs were injected with an admixture of viable Listeria and a methylcholanthrene-induced fibrosarcoma in a ratio of 1 bacterium to 100 tumor cells, Listeria had a marked capacity to inhibit tumor growth. This confirms an earlier study in our laboratory (M. M. Dustoor, A. Fulton, W. Croft, and A. A. Blazkovec, Infect. Immun. 23:54-60, 1979). At no time did animals exhibit overt symptoms of disease as a result of Listeria infection. Animals treated with antilymphocyte serum, which had previously been shown to abrogate T-cell functions, were no longer able to suppress Listeria-tumor cell mixtures. Treatment in vivo with carrageenan, a macrophage-inhibitory agent, also abrogated Listeria-mediated tumor inhibition. These results suggest that Listeria-mediated inhibition requires intact T-lymphocyte and macrophage function. Experiments in which Listeria was given in admixture with the tumor cells or in the opposite flank demonstrated that the antitumor effects require intimate association of the Listeria and tumor cells. Histopathological studies, showing that macrophages and lymphocytes are the predominant inflammatory cells present at sites of tumor destruction, further suggest a role for these cells in Listeria-mediated inhibition. Animals which had rejected prior Listeria-tumor cell inocula were resistant to rechallenge with the homologous tumor for more than 1 year. This work thus confirms in vitro studies demonstrating that both lymphocytes and macrophages are required for Listeria-mediated tumor inhibition to occur. This study demonstrates that viable Listeria can have potent antitumor effects without causing overt disease as a result of Listeria infection.

Antitumor activity of Listeria monocytogenes on a guinea pig fibrosarcoma

Listeria monocytogenes-mediated tumor inhibition was studied in strain 13 guinea pigs by using a methylcholanthrene-induced fibrosarcoma (MCA-1). Mixtures of Listeria and tumor cells in ratios of 1:100, 1:200, or 1:400 (Listeria:MCA-1 cells) led to significant suppression of tumor growth. Intralesional injection of tumors on day 6 posttransplantation led to the regression of a highly significant number of tumors. Animals receiving injections of Listeria, either in a mixture with tumor cells or intralesionally, displayed enhanced skin test reactivity to a tumor extract. Tumor regressors were resistant for at least 2 to 3 months after the initial transplant to rechallenge with MCA-1 cells. Thus, with this particular tumor-host system, Listeria was successfully employed as an antitumor agent with no visibly detrimental side effects to the host.

Bacteriological and histopathological evaluation of guinea pigs after infection with Listeria monocytogenes

Randomly bred guinea pigs were infected with Listeria monocytogenes using the intracardial, intravenous and intraperitoneal routes of infection. Doses of Listeria ranged from 5 to 1,000 x the 50% lethal dose based on the 50% lethal dose for intracardially injected Listeria. A complete necropsy was performed on all animals that died after infection. Gross and microscopic examination of tissues revealed major pathological features which include myocarditis, edema and congestion with interstitial pneumonitis present in the lungs, and fatty hepatic changes with focal necrosis. For all or a majority of the animals, large numbers of Listeria were likewise recovered from these organs and from lymph nodes, spleen, kidneys, and adrenal gland tissue. Of the three routes of infection used, guinea pigs were most susceptible to Listeria injected via the intracardial route. The relatively high lethal dose of listeric for the quinea pig, however, suggests that the organism is a low-grade pathogen for this species.