Identifying peripersonal space boundaries in newborns

Abstract

Peripersonal space immediately surrounds the body and can be represented in the brain as a multisensory and sensorimotor interface mediating physical and social interactions between body and environment. Very little consideration has been given to the ontogeny of peripersonal spatial representations in early postnatal life, despite the crucial roles of peripersonal space and its adaptive relevance as the space where infants' earliest interactions take place. Here, we investigated whether peripersonal space could be considered a delimited portion of space with defined boundaries soon after birth. Our findings showed for the first time that newborns' saccadic reaction times to a tactile stimulus simultaneous to sounds with different intensities changed based on the sound intensity. In particular, they were significantly faster when the sound was lounder than a critical intensity, in a pattern that closely resembled that showed by adults. Therefore, provided that sound intensity on its own can cue newborns' sound distance perception, we speculate that this critical distance could be considered the boundary of newborns' rudimentary peripersonal space. Altogether, our findings suggest that soon after birth peripersonal space may be already considered as a bounded portion of space, perhaps instrumental to drive newborns' attention towards events and people within it.

Figure 1

Saccadic reaction times in the Pilot Study. Mean sRTs (and SE) in response to the visual targets immediately following the audio-tactile stimulation, as function of the intensity of the sound. Significant comparisons are indicated (**p < 0.01).

Figure 2

Saccadic reaction times in Study 1. Mean sRTs (and SE) in response to the visual targets immediately following the audio-tactile (Audio-tactile stimulation group) or auditory (Auditory stimulation group) stimulation, as function of the intensity of the sound. Significant comparisons are indicated (**p < 0.001).

Figure 3

Experimental procedure. The newborns were presented with a flickering white circle on a black background for 3 s; then, one of the three (pilot study) or five (Study 1) possible auditory stimuli was presented for 2 s. At the same time, the newborns’ forehead was gently and slowly stroked (only once) with a paintbrush. In the meantime, the white circle kept flickering in order to keep the newborns’ attention focused in the centre of the screen. Finally, two peripheral targets appeared and remained on the screen for another 2 s, before the next trial started.