Infant Video Viewing and Salivary Cortisol Responses: A Randomized Experiment

Abstract

To test the hypothesis that salivary cortisol levels respond differently when infants play with blocks compared with watching a digital video disk (DVD). We conducted a randomized experiment in which 8- to 14-month-old infants either watched a DVD or played with blocks for 30 minutes. Serial salivary cortisol measurements were obtained and analyzed, and parental and infant responses and activities were recorded. Results were converted to standardized effect sizes (ESs) for clarity of presentation. A total of 49 infants (49% female, mean age 10.6 months) participated in the study. In linear regression analyses, there was a trend toward higher cortisol levels in the block group at the 35-minute collection point (ES = 0.47, P = .08) and significantly higher levels at 45 minutes (ES = 0.56, P = .04); these salivary cortisol levels reflect serum levels approximately 10 and 20 minutes into the activity period, respectively. The results were substantially the same in sensitivity analyses excluding the outliers. Viewing by infants of a DVD leads to different neuroendocrine responses than block play in a laboratory setting. The implications of these differences are currently unknown, but may suggest different means of cognitive engagement between interactive play and DVD viewing.