Spatial associations of number and pitch in human newborns

Humans use space to think, reason about, externally represent, and even talk about many dimensions (e.g., time, pitch height). One dimension that appears to exploit spatial resources is the mental representation of the numerosity of a set in the form of a mental number line. Although the horizontal number–space mapping is present from birth (small–left vs. large–right), it is unknown whether it extends to other spatial axes from birth or whether it is later acquired through development/experience. Moreover, newborns map changes in pitch height onto a vertical axis (low pitch–bottom vs. high pitch–top), but it is an open question whether it extends to other spatial axes. We presented newborns (N = 64 total, n = 16 per experiment, 0–4 days) with an auditory increase/decrease in magnitude along with a visual figure on a vertically oriented screen (bottom vs. top, change in number: Experiments 1 and 2; change in pitch: Experiment 3) or on a horizontally oriented screen (left vs. right, change in pitch: Experiment 4). Newborns associated changes in magnitude with a vertical axis only when experiencing an increase in magnitude (increase/up); however, the possibility that visuospatial biases could account for this asymmetric pattern are discussed. Newborns did not map changes in pitch horizontally (Experiment 4), in line with previous work showing that the horizontal mapping of number at birth does not generalize to other dimensions. These findings suggest that the flexible use of different spatial axes to map magnitude is not functional at birth and that the horizontal mapping of number might be privileged.