Search

Teaching is a powerful way to transmit knowledge, but with this power comes a hazard: When teachers fail to select the best set of evidence for the learner, learners can be misled to draw inaccurate inferences. Evaluating others' failures as teachers, however, is a nontrivial problem; people may fail to be informative for different reasons, and not all failures are equally blameworthy. How do learners evaluate the quality of teachers, and what factors influence such evaluations? Here, we present a Bayesian model of teacher evaluation that considers the utility of a teacher's pedagogical sampling given their prior knowledge. In Experiment 1 (N=1168), we test the model predictions against adults' evaluations of a teacher who demonstrated all or a subset of the functions on a novel device. Consistent with the model predictions, participants' ratings integrated information about the number of functions taught, their values, as well as how much the teacher knew. Using a modified paradigm for children, Experiments 2 (N=48) and 3 (N=40) found that preschool-aged children (2a, 3) and adults (2b) make nuanced judgments of teacher quality that are well-predicted by the model. However, after an unsuccessful attempt to replicate the results with preschoolers (Experiment 4, N=24), in Experiment 5 (N=24) we further investigate the development of teacher evaluation in a sample of seven- and eight-year-olds. These older children successfully distinguished teachers based on the amount and value of what was demonstrated, and their ability to evaluate omissions relative to the teacher’s knowledge state was related to their tendency to spontaneously reference the teacher's knowledge when explaining their evaluations. In sum, our work illustrates how the human ability to learn from others supports not just learning about the world but also learning about the teachers themselves. By reasoning about others' informativeness, learners can evaluate others' teaching and make better learning decisions.

Samples of 1:1 and 2:1 poly(styrene-co-maleic anhydride) films were exposed to radiation from a QUVB-313 light source under atmospheric oxygen and their photooxidative reactions studied using FTIR, UV-VIS and 13C NMR spectroscopy. A major finding was that the bulk of the photodegradation resulted in loss of low molecular weight volatile fragments from the polymer chains as demonstrated by the continuous decrease in intensity of anhydride (1780 cm−1) and aromatic (704 cm−1) bands in the infrared spectrum with only minor changes in the 13C NMR spectra of the residual polymers. The UV-VIS spectra showed very significant increases in absorbance up to approximately 450 nm. Combined with the formation of new hydroxyl (3500-3000 cm−1), carbonyl (1725 cm−1) and CO (1240 cm−1) bands in the FTIR spectra, the data have enabled a scheme of chemical changes to be proposed to account for the early degradative reactions which lead to the material loss. Changes in the FTIR and UV-VIS spectra occurred more rapidly for the 2:1 copolymer than for the 1:1 copolymer, indicating that an increase in the proportion of styrene units decreased the stability of poly(styrene-co-maleic anhydride) towards photooxidation on exposure to the QUVB-313 light source.