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Zipfian distributions facilitate learning novel word-referent mappings
Children are exposed to Zipfian word distributions during language acquisition. Previous studies suggest that such skewed environments confer a learnability advantage in tasks that require the learner to identify the units to be learned, as in word-segmentation or cross-situational learning. The facilitative effect has been attributed to contextual facilitation from the high frequency items in learning the lower frequency items, or to improved error-based learning due to the lower entropy of Zipfian distributions. Here, we ask whether Zipfian distributions facilitate learning beyond unit-identification, as expected under the improved error-based learning explanation. We tested children’s learning of noun-referent mappings in a learning task where each item was presented in isolation during training. Children’s learning was improved overall, and for low frequency items, in two skewed environments with different entropy levels compared to a uniform environment. These results extend the facilitative effect of Zipfian distributions to additional learning tasks, beyond unit identification
Relative Importance of Nasopharyngeal versus Oropharyngeal Sampling for Isolation of Streptococcus pneumoniae and Haemophilus influenzae from Healthy and Sick Individuals Varies with Age
Streptococcus pneumoniae and Haemophilus influenzae carriage is a useful index for measuring the emergence of resistance and outcome in vaccination trials. We performed a study to determine which sampling site, nasopharynx (NP) or oropharynx (OP), yields the highest rate of S. pneumoniae and H. influenzae isolation at different ages. Both NP and OP cultures were obtained from 216 children aged <60 months and their mothers. The total S. pneumoniae carriage rate was 68% among children and 15% among mothers (P < 0.001). Using NP alone for the isolation of S. pneumoniae would have missed 2, 2, and 42% and using OP alone would have missed 77, 66, and 45% of S. pneumoniae in children aged 0 to 23 months, 24 to 59 months, and mothers, respectively. Using NP cultures alone for H. influenzae would have missed 23, 24, and 81% of the isolates, respectively. The respective figures for H. influenzae isolation from OP alone are 38, 29, and 9%. In children, S. pneumoniae was carried mainly in the NP while H. influenzae was equally carried in the NP and OP. In mothers, S. pneumoniae was carried equally in the NP and OP while H. influenzae was carried significantly more often in the OP. In children, H. influenzae colonization increased during illness, mainly in the NP. Culturing only one site significantly reduced the recovery of H. influenzae at all ages. NP cultures for S. pneumoniae detected close to 100% of isolates in children but only 58% of isolates in mothers