Abstract
Head‐cocking of 15 infant marmosets (Callithrix jacchus) was scored from Day 1 to 60 of postnatal life, the growth period with overproduction of interneuronal synapses. Head‐cocking was scored during four 30 min intervals daily, including angle of head‐cocking and objects being fixated. Mean age of onset of head‐cocking was Day 13 (±1.3) and frequency increased to a fixed rate by Day 24–29, at the time of maturation of the foveal representation in layer 6 of the visual cortex, thus lending further support to the importance of head‐cocking to visual processing. The most common distance of objects fixated during head‐cocking was up to .5 m. Angle of head‐cocking increased with age, and some asymmetry of direction was noted. Fewer head‐cocking events occurred in the morning than in the afternoon. We also scored anogenital licking of offspring. Head‐cocking occurred at higher levels in marmosets receiving more anogenital licking. As this was associated positively with increased exploration, head‐cocking may be regarded as an exploratory behavior. © 2006 Wiley Periodicals, Inc. Dev Psychobiol 48: 551–560, 2006.