A home-based progressive-ratio task for assessing food reinforcement in infancy: Developmental sensitivity at 9 and...

The relative reinforcing value of food (RRV^Food) is theorized to emerge early and contribute to obesity risk. We examined whether a matched set of solid foods elicited differentiation between food and nonfood reinforcement at 9 (n = 110) and 12 (n = 133) months of age. We hypothesized that infants would respond for both reinforcers at both age points with enough variability for individual-differences analyses, and that RRV^Food would relate to food consumption, appetitive traits, and weight-for-length z-score (WLZ) more strongly at 12 months. In a longitudinal subsample (n = 70), we further hypothesized stability in responding across age points and explored how responding to each reinforcer changed over time. Infants completed a progressive-ratio lever-press task at 9 and 12 months to earn food (cereal) and nonfood (block) reinforcers. Absolute reinforcing value (ARV) was operationalized as lever presses for each reinforcer; RRV^Food was operationalized as ARV^Food/ARV^Nonfood ratio. Mothers completed the Children's Eating Behavior Questionnaire-Toddler (CEBQ-T) to index food enjoyment and food responsiveness. Food reinforcer consumption and WLZ were also assessed. At 9 months, ARV^Food and ARV^Nonfood positively correlated, but RRV^Food was not associated with food reinforcer consumption, appetitive traits, or WLZ. By 12 months, RRV^Food was positively associated with enjoyment of food, and ARV^Food was positively associated with WLZ. Findings suggest that food reinforcement is more meaningfully differentiated from nonfood reinforcement at 12 months than at 9 months. Whether this reflects genuine developmental consolidation of food motivation or measurement limitations inherent to testing younger infants remains to be determined.