Quantifying Sources of Variability in Infancy Research Using the Infant-Directed-Speech Preference

Psychological scientists have become increasingly concerned with issues related to methodology and replicability, and infancy researchers in particular face specific challenges related to replicability: For example, high-powered studies are difficult to conduct, testing conditions vary across labs, and different labs have access to different infant populations. Addressing these concerns, we report on a large-scale, multisite study aimed at (a) assessing the overall replicability of a single theoretically important phenomenon and (b) examining methodological, cultural, and developmental moderators. We focus on infants’ preference for infant-directed speech (IDS) over adult-directed speech (ADS). Stimuli of mothers speaking to their infants and to an adult in North American English were created using seminaturalistic laboratory-based audio recordings. Infants’ relative preference for IDS and ADS was assessed across 67 laboratories in North America, Europe, Australia, and Asia using the three common methods for measuring infants’ discrimination (head-turn preference, central fixation, and eye tracking). The overall meta-analytic effect size (Cohen’s d) was 0.35, 95% confidence interval = [0.29, 0.42], which was reliably above zero but smaller than the meta-analytic mean computed from previous literature (0.67). The IDS preference was significantly stronger in older children, in those children for whom the stimuli matched their native language and dialect, and in data from labs using the head-turn preference procedure. Together, these findings replicate the IDS preference but suggest that its magnitude is modulated by development, native-language experience, and testing procedure

Bond strength of short lap splices in RC beams confined with steel stirrups or external CFRP

This paper investigates the bond behaviour of lapped steel bars using fifteen RC beams tested in flexure. Twelve of the beams were designed to fail by bond splitting at midspan, where the main flexural reinforcement was lapped 10 bar diameters. The parameters studied include the amount and type of confinement at midspan (no confinement, internal steel stirrups or externally bonded carbon FRP), concrete cover and bar size. The results show that the CFRP confinement enhanced the bond strength of the lapped bars by up to 49 % with reference to unconfined beams, and improved significantly the overall behaviour of the specimens. The experimental results are compared with existing models to predict the bond strength enhancement provided by CFRP confinement. It is shown that existing models overestimate considerably the CFRP strains and show a large scatter when predicting experimental results. Based on the test results, a new approach to predict the bond strength enhancement due to CFRP confinement is proposed. This can be used during the assessment and strengthening of substandard RC constructions. © 2013 RILEM