Assessing motivation to move and its relationship to motor development in infancy.

Motivation to move has typically been a post hoc explanation for infants' discovery of new patterns of behavior. As a first step to studying motivation to move directly, we qualitatively assessed motivation to move and measured its relationship to motor development in infancy. We observed 27 infants longitudinally from ages 7 to 12 months. Every 3 weeks we assessed infants' motor motivation based on persistence, activity level, activity preference, and stimulus strength needed to elicit movement. We documented the onset of sitting, pulling-to-stand, crawling and cruising, as well as infants' overall motor development as measured with the Alberta Infant Motor Scale (AIMS). Motor motivation increased over the course of the study and we identified two distinct motivation profiles. Strongly motivated infants had earlier onsets for all four motor milestones than weakly motivated infants (all p-values <0.05). Infants' motivation to move score was positively correlated with their AIMS percentile at the same and subsequent sessions. These findings provide empirical evidence for a motivational cascade whereby motivation to move and motor development enjoy a reciprocal relationship. These findings have important clinical implications for children with motor delay, suggesting that evaluation of motivation could be included as part of the assessment procedure so that both treatment and expectations can be tailored appropriately.