Infants laugh by 4 months, but whether they understand humour based on social or cognitive factors is unclear. We conducted two longitudinal studies of 4-, 6-, and 8-month-olds (N = 60), and 5-, 6-, and 7-month-olds (N = 53) to pinpoint the onset of independent humour perception and determine when social and cognitive factors are most salient. Infants were shown six events in randomized repeated-measures designs: two ordinary events and two absurd iterations of those events, with parents’ affect manipulated (laugh or neutral) during the latter. Four-month-olds did not smile/laugh more at absurd events, but exhibited a significant heart rate deceleration. Five-month-olds independently appraised absurd events as humorous, smiling/laughing despite their parents’ neutrality. Parent laughter did not influence infants of any age to smile more, but captured 4-month-olds’ attention. Results suggest that 4-month-olds laugh in response to social cues, while 5-month-olds’ can laugh in response to cognitive features.

Strollers and backpacks are employed early, frequently and throughout the first year, with parents overwhelmingly using strollers. However, because these transport modalities put infants in different proximities to caregivers, postures, and states of alertness, their use may translate to different opportunities that are of developmental consequence, particularly with regard to language. We used GoPro technology in a within subjects counter-balanced design to measure dyadic vocalizations in strollers and backpacks with 7-to-11-month-old infants. Parent-infant dyads (=36), who regularly used both transport modes took two 8-minute walks in their own neighborhoods using their own carriers while wearing lightweight head-mounted GoPros. There was significantly more parent speech, infant vocalizations, dyadic conversations and infant-initiated speech in backpacks, as well as more head motion consistent with visual scanning by infants. Backpacks appear to be a practical way to encourage more engaging, language-enriched developmental opportunities in the critical first year.

No abstract