Bootstrapping the lexicon: a computational model of infant speech segmentation

Prelinguistic infants must find a way to isolate meaningful chunks from the continuous streams of speech that they hear. BootLex, a new model which uses distributional cues to build a lexicon, demonstrates how much can be accomplished using this single source of information. This conceptually simple probabilistic algorithm achieves significant segmentation results on various kinds of language corpora - English, Japanese, and Spanish; child- and adult-directed speech, and written texts; and several variations in coding structure - and reveals which statistical characteristics of the input have an influence on segmentation performance. BootLex is then compared, quantitatively and qualitatively, with three other groups of computational models of the same infant segmentation process, paying particular attention to functional characteristics of the models and their similarity to human cognition. Commonalities and contrasts among the models are discussed, as well as their implications both for theories of the cognitive problem of segmentation itself, and for the general enterprise of computational cognitive modeling.     

A Social Ecological Model of Syndemic Risk affecting Women with and At-Risk for HIV in Impoverished Urban Communities

Syndemic risk is an ecological construct, defined by co‐occurring interdependent socio‐environmental, interpersonal and intrapersonal determinants. We posited syndemic risk to be a function of violence, substance use, perceived financial hardship, emotional distress and self‐worth among women with and at‐risk for HIV in an impoverished urban community. In order to better understand these interrelationships, we developed and validated a system dynamics (SD) model based upon peer‐reviewed literature; secondary data analyses of a cohort dataset including women living with and at‐risk of HIV in Bronx, NY (N = 620); and input from a Bronx‐based community advisory board. Simulated model output revealed divergent levels and patterns of syndemic risk over time across different sample profiles. Outputs generated new insights about how to effectively explore multicomponent multi‐level programs in order to strategically develop more effective services for this population. Specifically, the model indicated that effective multi‐level interventions might bolster women’s resilience by increasing self‐worth, which may result in decreased perceived financial hardship and risk of violence. Overall, our stakeholder‐informed model depicts how self‐worth may be a major driver of vulnerability and a meaningful addition to syndemic theory affecting this population.     

Effects of chlordiazepoxide on pausing during rich-to-lean transitions

Extended pausing during discriminable transitions from rich-to-lean conditions can be viewed as escape (i.e., rich-to-lean transitions function aversively). Thus, an anxiolytic drug would be predicted to mitigate the aversiveness and decrease pausing. In the current experiment, pigeons' key pecking was maintained by a multiple fixed-ratio fixed-ratio schedule of rich (i.e., larger) or lean (i.e., smaller) reinforcers. Intermediate doses (3.0-10.0 mg/kg) of chlordiazepoxide differentially decreased median pauses during rich-to-lean transitions. Relatively small decreases in pauses occurred during lean-to-lean and rich-to-rich transitions. Effects of chlordiazepoxide on pausing occurred without appreciable effects on run rates. These findings suggest that signaled rich-to-lean transitions function aversively.