Differences in vocal fundamental (F0) and average formant (Fn) frequencies covary with body size in most terrestrial mammals, such that larger organisms tend to produce lower frequency sounds than smaller organisms, both between species and also across different sex and life-stage morphs within species. Here we examined whether three-month-old human infants are sensitive to the relationship between body size and sound frequencies. Using a violation-of-expectation paradigm, we found that infants looked longer at stimuli inconsistent with the relationship-that is, a smaller organism producing lower frequency sounds, and a larger organism producing higher frequency sounds-than at stimuli that were consistent with it. This effect was stronger for fundamental frequency than it was for average formant frequency. These results suggest that by three months of age, human infants are already sensitive to the biologically relevant covariation between vocalization frequencies and visual cues to body size. This ability may be a consequence of developmental adaptations for building a phenotype capable of identifying and representing an organism's size, sex and life-stage.

Cognitive scientists have focused too narrowly on the acquisition of data and on the methods to extract patterns from those data. We argue that a successful science of the mind requires widening our focus to include the problems being solved by cognitive processes. Frameworks that characterize cognitive processes in terms of instrumental problem-solving, such as those within the evolutionary social sciences, become necessary if we wish to discover more accurate descriptions of those processes.

Humans irresistibly perceive certain events as causal. We show, for the first time, that there is not one monolithicrepresentation of causality in perception. Rather, there are multiple categories of causal events in perception, one of which isconstrained by an approximation of a Newtonian mechanical principle: in an elastic collision, a struck object cannot move atmore than double the speed of the object striking it. We show that adults are sensitive to causal (but not non-causal) eventsthat violate this principle in a visual search task (Experiment 1), that this sensitivity is due to a categorical boundary and notthe salience of this event (Experiment 2), and that the threshold for detecting these events approximates this Newtonian limit(Experiment 3). Finally, we argue that categorical boundaries are a core feature of causal perception, as they are present aroundthe age at which causal perception first emerges (Experiment 4).