Most music is temporally organized within a metrical hierarchy, having nested periodic patterns that give rise to the experience of stronger (downbeat) and weaker (upbeat) events. Musical meter presumably makes it possible to dance, sing, and play instruments in synchrony with others. It is nevertheless unclear whether or not listeners perceive multiple levels of periodicity simultaneously, and if they do, when and how they learn to do this. We tested children, adolescents, and musically trained and untrained adults with a new meter perception task. We presented excerpts of human-performed music paired with metronomes that matched or mismatched the metrical structure of the music at two hierarchical levels (beat and measure), and asked listeners to provide a rating of fit of metronome and music. Fit ratings suggested that adults with and without musical training were sensitive to both levels of meter simultaneously, but ratings were more strongly influenced by beat-level than by measure-level synchrony. Sensitivity to two simultaneous levels of meter was not evident in children or adolescents. Sensitivity to the beat alone was apparent in the youngest children and increased with age, whereas sensitivity to the measure alone was not present in younger children (5-8-year-olds). These findings suggest a prolonged period of development and refinement of hierarchical beat perception, and surprisingly weak overall ability to attend to two beat levels at the same time across all ages.

The sclera, the eye's tough outer layer, is, among primates, white only in humans, providing the ground necessary for the display of colors that vary in health and disease. The current study evaluates scleral color as a cue of socially significant information about health, attractiveness, and age by contrasting the perception of eyes with normal whites with copies of those eyes whose whites were reddened, yellowed, or further whitened by digital editing. Individuals with red and yellow sclera were rated to be less healthy, less attractive, and older than individuals with untinted control sclera. Individuals with whitened, "super-white" sclera were rated as younger, although not more healthy or attractive, than controls. In humans, clear, white sclera may join such traits as smooth skin and long, lustrous hair as signs of health, beauty, and reproductive fitness. The evolution of a white sclera may have contributed to the emergence of humans as a social species.

Most music is temporally organized within a metrical hierarchy, having nested periodic patterns that give rise to the experience of stronger (downbeat) and weaker (upbeat) events. Musical meter presumably makes it possible to dance, sing, and play instruments in synchrony with others. It is nevertheless unclear whether or not listeners perceive multiple levels of periodicity simultaneously, and if they do, when and how they learn to do this. We tested children, adolescents, and musically trained and untrained adults with a new meter perception task. We presented excerpts of human-performed music paired with metronomes that matched or mismatched the metrical structure of the music at two hierarchical levels (beat and measure), and asked listeners to provide a rating of fit of metronome and music. Fit ratings suggested that adults with and without musical training were sensitive to both levels of meter simultaneously, but ratings were more strongly influenced by beat-level than by measure-level synchrony. Sensitivity to two simultaneous levels of meter was not evident in children or adolescents. Sensitivity to the beat alone was apparent in the youngest children and increased with age, whereas sensitivity to the measure alone was not present in younger children (5-8-year-olds). These findings suggest a prolonged period of development and refinement of hierarchical beat perception, and surprisingly weak overall ability to attend to two beat levels at the same time across all ages.

Movement to music is a universal human behavior, yet little is known about how observers perceive audiovisual synchrony in complex musical displays such as a person dancing to music, particularly during infancy and childhood. In the current study, we investigated how perception of musical audiovisual synchrony develops over the first year of life. We habituated infants to a video of a person dancing to music and subsequently presented videos in which the visual track was matched (synchronous) or mismatched (asynchronous) with the audio track. In a visual-only control condition, we presented the same visual stimuli with no sound. In Experiment 1, we found that older infants (8-12months) exhibited a novelty preference for the mismatched movie when both auditory information and visual information were available and showed no preference when only visual information was available. By contrast, younger infants (5-8months) in Experiment 2 did not discriminate matching stimuli from mismatching stimuli. This suggests that the ability to perceive musical audiovisual synchrony may develop during the second half of the first year of infancy.

In recent years, interest has grown in potential links between abilities in musical rhythm and the development of language and reading, as well as in using music lessons as an intervention or diagnostic tool for individuals at risk for language and reading delays. Nevertheless, the development of abilities in musical rhythm is a relatively new area of study. In this article, we review knowledge about the development of musical rhythm, highlighting key musical structures of rhythm, beat, and meter, and suggesting areas of inquiry. Further research is needed to understand how children acquire the perceptual and cognitive underpinnings of universal musical behaviors such as dancing, clapping, and singing in time with music.