Robot Reinforcement and Error-Based Movement Learning in Infants With and Without Cerebral Palsy

Background Prone mobility, central to development of diverse psychological and social processes that have lasting effects on life participation, is seldom attained by infants with cerebral palsy (CP) and has no tested interventions. Reinforcement learning (RL) and error-based movement learning (EBL) offer novel intervention possibilities. Objective This study examined movement learning strategies in infants with or at risk for CP using RL and EBL during acquisition of prone locomotion. Design The study was a randomized trial that used repeated measures. Setting The study setting was a university physical therapy clinic in the United States. Patients Thirty infants aged 4.5 to 6.5 months participated in the study: 24 had or were at risk for CP, and 6 were typically developing. Intervention Infants with and at risk for CP were randomly assigned to a combination of RL and EBL (SIPPC-RE), or RL only (SIPPC-R) conditions. Infants with typical development comprised the RL-only reference group (SIPPC-TD). Infants trained in prone locomotion with the Self-Initiated Prone Progression Crawler (SIPPC) robotic system for three 5-minute trials, twice a week for 12 weeks in their homes or child care. All training sessions were videotaped for behavioral coding. Measurements The SIPPC gathered robot and infant trunk/limb movement data. Randomized 2-way analysis of variance with repeated measures and Pearson r to analyze the data was used. Results Results included the number of arm movements and trial-and-error activity distinguished between the SIPPC-RE and SIPPC-R groups. The mean change in arm movements from baseline for the SIPPC-RE and SIPPC-R groups was 4.8 m and -7.0 m, respectively. The mean differences in rotational amplitude (trial and error) from baseline to the end of the study were 278 degrees and 501 degrees, respectively. These changes were correlated with distance traveled and goal-directed movements. The latter increased over the 12 weeks for the SIPPC-RE and SIPPC-TD groups, but not the SIPPC-R group. Limitations The CP groups were unequal due to reassignment and did not include a typically developing comparison group of a combination of RL and EBL. Conclusion These findings suggest movement learning and retention in infants with CP is differentially affected by the use of RL and EBL, with a combination of both showing more promise than RL alone. The findings also implicate cognition, type of brain insult, emergence of reaching, and muscle force production, which must be explored in future studies.