Perception of visual and audiovisual trajectories toward and away from the body in the first postnatal year.

Perceiving motion in depth is important in everyday life, especially motion in relation to the body. Visual and auditory cues inform us about motion in space when presented in isolation from each other, but the most comprehensive information is obtained through the combination of both of these cues. We traced the development of infants' ability to discriminate between visual motion trajectories across peripersonal space and to match these with auditory cues specifying the same peripersonal motion. We measured 5-month-old (n = 20) and 9-month-old (n = 20) infants' visual preferences for visual motion toward or away from their body (presented simultaneously and side by side) across three conditions: (a) visual displays presented alone, (b) paired with a sound increasing in intensity, and (c) paired with a sound decreasing in intensity. Both groups preferred approaching motion in the visual-only condition. When the visual displays were paired with a sound increasing in intensity, neither group showed a visual preference. When a sound decreasing in intensity was played instead, the 5-month-olds preferred the receding (spatiotemporally congruent) visual stimulus, whereas the 9-month-olds preferred the approaching (spatiotemporally incongruent) visual stimulus. We speculate that in the approaching sound condition, the behavioral salience of the sound could have led infants to focus on the auditory information alone, in order to prepare a motor response, and to neglect the visual stimuli. In the receding sound condition, instead, the difference in response patterns in the two groups may have been driven by infants' emerging motor abilities and their developing predictive processing mechanisms supporting and influencing each other.

Visual objects approaching the body modulate subsequent somatosensory processing at 4 months of age.

We asked whether, in the first year of life, the infant brain can support the dynamic crossmodal interactions between vision and somatosensation that are required to represent peripersonal space. Infants aged 4 (n = 20, 9 female) and 8 (n = 20, 10 female) months were presented with a visual object that moved towards their body or receded away from it. This was presented in the bottom half of the screen and not fixated upon by the infants, who were instead focusing on an attention getter at the top of the screen. The visual moving object then disappeared and was followed by a vibrotactile stimulus occurring later in time and in a different location in space (on their hands). The 4-month-olds' somatosensory evoked potentials (SEPs) were enhanced when tactile stimuli were preceded by unattended approaching visual motion, demonstrating that the dynamic visual-somatosensory cortical interactions underpinning representations of the body and peripersonal space begin early in the first year of life. Within the 8-month-olds' sample, SEPs were increasingly enhanced by (unexpected) tactile stimuli following receding visual motion as age in days increased, demonstrating changes in the neural underpinnings of the representations of peripersonal space across the first year of life.

Identifying peripersonal space boundaries in newborns.

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.

Multisensory perception of looming and receding objects in human newborns.

When newborns leave the enclosed spatial environment of the uterus and arrive in the outside world, they are faced with a new audiovisual environment of dynamic objects, actions and events both close to themselves and further away. One particular challenge concerns matching and making sense of the visual and auditory cues specifying object motion [1-5]. Previous research shows that adults prioritise the integration of auditory and visual information indicating looming (for example [2]) and that rhesus monkeys can integrate multisensory looming, but not receding, audiovisual stimuli [4]. Despite the clear adaptive value of correctly perceiving motion towards or away from the self - for defence against and physical interaction with moving objects - such a perceptual ability would clearly be undermined if newborns were unable to correctly match the auditory and visual cues to such motion. This multisensory perceptual skill has scarcely been studied in human ontogeny. Here we report that newborns only a few hours old are sensitive to matches between changes in visual size and in auditory intensity. This early multisensory competence demonstrates that, rather than being entirely naïve to their new audiovisual environment, newborns can make sense of the multisensory cue combinations specifying motion with respect to themselves.

Trajectory Discrimination and Peripersonal Space Perception in Newborns.

The ability to discriminate the trajectories of moving objects is highly adaptive and fundamental for physical and social interactions. Therefore, we could reasonably expect sensitivity to different trajectories already at birth, as a precursor of later communicative and defensive abilities. To investigate this possibility, we measured newborns' looking behavior to evaluate their ability to discriminate between visual stimuli depicting motion along different trajectories happening within the space surrounding their body. Differently from previous studies, we did not take into account defensive reactions, which may not be elicited by impending collision as newborns might not categorize approaching stimuli as possible dangers. In two experiments, we showed that newborns display a spontaneous visual preference for trajectories directed toward their body. We found this visual preference when visual stimuli depicted motion in opposite directions (approaching vs. receding) as well as when they both moved toward the peripersonal space and differed only in their specific target (i.e., the body vs. the space around it). These findings suggest that at birth human infants seem to be already equipped with visual mechanisms predisposing them to perceive their presence in the environment and to adaptively focus their attention on the peripersonal space and their bodily self.

Newborn Body Perception: Sensitivity to Spatial Congruency.

Studies on adults have demonstrated that the perception our own body can be manipulated by varying both temporal and spatial properties of multisensory information. While human newborns are capable of detecting the temporal synchrony of visuo-tactile body-related cues, it remains unknown whether they also utilise spatial information for body perception. Twenty newborns were presented with a video of an infant's face touched with a paintbrush, while their own face was touched either in the spatially congruent, or an incongruent, location. We found that newborns show a visual preference for spatially congruent synchronous events, supporting the view that newborns have a rudimentary sense of their own body.