An Analysis of Methodological Differences in Longitudinal Studies of Infant Manual Preference

Studies on infant manual laterality can be very similar in terms of the goals of the research, but they often show wide variability in several aspects of methodological approaches. This can be problematic when researchers directly compare findings from studies that employ different methodologies. The most common methodological inconsistencies are how many trials are utilized, which behaviors are observed, and how bilateral behaviors are addressed in computations. Here we aim to address whether methodological differences can lead to dissimilar conclusions about patterns in infant manual behaviors like laterality and coupling for three versus eight trials, reach versus grasp actions, and when bilateral behaviors are removed or retained. We performed secondary analysis on 32 infants followed longitudinally for the first and second year of life. The ages that infants were observed ranged from 6.0 to 16.8 months. Analyses were conducted on all infants together and then again when infants were divided into three developmental age groups. Among the comparisons we investigated, we found a high degree of concordance between coupling and laterality quotients when comparing the first three versus the first eight trials of testing. We found fewer similarities between coupling and laterality quotients when comparing reaching behavior versus grasping responses and between laterality quotients when we retained or removed bilateral behaviors. We provide suggestions for best practices in conducting longitudinal research on infant manual laterality, as well as a caution against the prevalent tendency to directly compare research employing different methodology.