Startle reflex modification by attention and affective state in three and five-month-old infants

Modulation of the startle response is an objective indicator of emotionality and attention in infancy and adulthood. In the present study, 13 three-month and 13 five-month-old infants were tested in a new non-invasive whole body acoustic startle protocol. The aim was to investigate the development of the interaction between attention and emotion in the startle modification. While infants were on an infant-seat, interacting with their mothers and playing with objects, a noise burst was presented to elicit the reflex. The infant-seat, opportunely equipped, permitted a computerized measurement of the startle motor response. Each session was videotaped. Attentive behavior was coded frame-by-frame as well as smiling and distress behavior. Only at five months, startle latency was reduced when the infants were engaged in attention relative to control trials. Both groups presented a startle modification based on the dominant, positive or negative, affective state exhibited during the entire session.