Bivalency is costly: bivalent stimuli elicit cautious responding

When performing tasks in alternation, substantial slowing occurs when the stimuli have features relevant to both tasks (i.e., when stimuli are bivalent as opposed to univalent). One possible source of this slowing, herein called a bivalency cost, is that encountering bivalent stimuli leads to a more cautious response style. To investigate this, we employed a paradigm that required performing three simple tasks, with bivalent stimuli occasionally encountered on one task. The results show that regardless of the feature overlap among the stimuli used for the different tasks, the introduction of bivalent stimuli slowed responding on all tasks and it was accompanied by a decrease in response errors. Overall, it appears that bivalent stimuli recruit a more cautious approach to task-switching performance.     

Taxonic structure of infant reactivity: evidence from a taxometric perspective

Previously, we proposed a theoretical framework that classified infants into qualitative categories of reactivity, rather than on a continuous dimension. The present research used an objective statistical procedure (maximum covariance analysis, or MAXCOV) to determine if a qualitative latent structure, consistent with our theoretical conjectures, would be found to underlie quantitative indices of reactivity to stimuli in a sample of 599 four-month-old infants. Results of the MAXCOV analysis showed clear evidence of a latent discontinuity underlying the behavioral measures of infant reactivity. The base rate of the latent class (or taxon) was estimated at 10%. Infants within the putative high-reactivity taxon, compared with infants not in the taxon, were elevated on measures of behavioral inhibition at 4.5 years. These results provide objective empirical support for a central tenet in our theoretical model by supporting the taxonicity of infant reactivity.     

Realism about laws

This paper explores the idea that laws express relationships between properties or universals as defended in Michael Tooley's recent book Causation: A Realist Approach. I suggest that the most plausible version of realism will take a different form than that advocated by Tooley. According to this alternative, laws are grounded in facts about the capacities and powers of particular systems, rather than facts about relations between universals. The notion of lawfulness is linked to the notion of invariance, rather than to the metaphysical notion of a necessary connection.