Four-day-old human neonates look longer at non-biological motions of a single point-of-light

Abstract

Background: Biological motions, that is, the movements of humans and other vertebrates, are characterized by dynamic regularities that reflect the structure and the control schemes of the musculo-skeletal system. Early studies on the development of the visual perception of biological motion showed that infants after three months of age distinguished between biological and non-biological locomotion.

Methodology/principal findings: Using single point-light motions that varied with respect to the "two-third-power law" of motion generation and perception, we observed that four-day-old human neonates looked longer at non-biological motions than at biological motions when these were simultaneously presented in a standard preferential looking paradigm.

Conclusion/significance: This result can be interpreted within the "violation of expectation" framework and can indicate that neonates' motion perception - like adults'-is attuned to biological kinematics.

Figure 1

Stimuli and Experimental Design. (A) Geometry (line) and Cartesian coordinates (markers) of the biological stimuli. The arrow indicates the direction of motion. The circular outline shows the starting position and the relative size of the light-spot with respect to the trajectory. (B) Tangential velocity of the elliptical (line) and circular (dashed line) biological stimuli. (C) Non-biological motions derived from the biological coordinates. Geometry and kinematics were inverted. (D) Experimental design. The neonates were assigned to one of the four sub-groups defined by the combination of the stimulus geometry (ellipse or circle) and of the screen (left or right) displaying the biological motion (white points)

Figure 2

Frequency of the three behaviors in the neonates sample as a function of time. It provides an estimate of the time-varying probability of observing a given behavior. The gray bar corresponds to the 1 s pause. The data were fitted with a fourth order polynomial to figure out the global trend.