Stimulus-Presentation Probability Influences Newborns' Head Orientation to Sound

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Abstract
Although newborn infants are capable of turning their heads toward laterally-presented sounds, the incidence of such responding varies across studies. Previous work suggests that as the probability of a laterally-presented sound increases head-turning performance improves. To test this “lateral-stimulus-presentation probability” hypothesis, we presented 30 alert newborns with a rattle sound from a lateral source on either 1/4, 2/4, or 3/4 of all sound trials. On remaining sound trials the rattle came from a loudspeaker located above the infant's head. For 12 infants all lateral trials were presented consecutively; these trials were spaced across the session for the other infants. The likelihood of correct head turning increased linearly as the lateral-stimulus-presentation probability increased. The distribution of lateral trials did not influence the incidence of correct head turning.