Seeing Touches Early in Life

Margaret Addabbo, Elena Longhi, Nadia Bolognini, Irene Senna, Paolo Tagliabue, Viola Macchi Cassia, Chiara Turati, Marcello Costantini
2015 PLoS ONE  
The sense of touch provides fundamental information about the surrounding world, and feedback about our own actions. Although touch is very important during the earliest stages of life, to date no study has investigated infants' abilities to process visual stimuli implying touch. This study explores the developmental origins of the ability to visually recognize touching gestures involving others. Looking times and orienting responses were measured in a visual preference task, in which
more » ... ts were simultaneously presented with two videos depicting a touching and a no-touching gesture involving human body parts (face, hand) and/or an object (spoon). In Experiment 1, 2-day-old newborns and 3-month-old infants viewed two videos: in one video a moving hand touched a static face, in the other the moving hand stopped before touching it. Results showed that only 3-month-olds, but not newborns, differentiated the touching from the no-touching gesture, displaying a preference for the former over the latter. To test whether newborns could manifest a preferential visual response when the touched body part is different from the face, in Experiment 2 newborns were presented with touching/no-touching gestures in which a hand or an inanimate object -i.e., a spoon-moved towards a static hand. Newborns were able to discriminate a handto-hand touching gesture, but they did not manifest any preference for the object-to-hand touch. The present findings speak in favour of an early ability to visually recognize touching gestures involving the interaction between human body parts. so far no study has investigated infants' ability to visually distinguish between touching and no-touching gestures. Conversely, visual processing of touch has been extensively investigated in adults [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] . Recent neuroimaging studies have shown that, when adults witness another person or even an object being touched by a human agent, neural circuitries normally recruited during the self-experience of touch are activated [4, [7] [8] [9] [10] [11] [12] . Activation of the somatosensory cortices during touch observation is further supported by brain stimulation [5, 6, 13 ] and lesion studies [14] , the first showing the selectivity of the human somatosensory cortex for the visual processing of contact between human body-parts [13] . This evidence is in line with the view that adult humans are equipped with a "tactile mirror system", which matches observed touch with the sense of one's own touch [15] . This system has been proposed to play a key role in social perception and empathy [5, 6, 13, [15] [16] [17] . Already during prenatal life, infants acquire extensive somatosensory-motor experience. In the womb fetuses perform different hand movements directed towards the environment, like the uterine wall, the umbilical cord or their own body, in particular the face [18, 19] . These movements appear to be well organized and coordinated [20, 21, 22] . At 24 weeks of gestation, half of the fetal arm movements result in hands touching the mouth [21], with the frequency of touch for lower and perioral regions of the face increasing significantly with gestational age. Hand-to-face gestures represent one of the most frequent activities during fetal life, and they remain a prominent behavior during the earlier stages of postnatal life [23] . In fact, neonates often touch their face, and especially their mouth, during their waking hours [24, 25] . Possibly due to prenatal somatosensory experiences, neonates seem to have some knowledge about their body immediately after birth [26, 27, 28] . For example, they are able to discriminate between external touch and self-stimulation, displaying rooting responses when their cheek is touched by the finger of somebody else, but not by their own finger [27] . Likewise, newborns imitate observed facial and hand movements [29, 30] . With respect to the visual processing of tactile bodily signals, Zmyj and colleagues [31] have shown that 7-and 10-month-old infants are sensitive to intersensory visual-tactile contingency. When presented with two videos displaying a lifelike-baby doll whose legs are touched by a hand, infants look longer at the video in which the touch is contingent with a tactile stimulation on their own leg than at a non-contingent touch. By contrast, when presented with a video showing oblong wooden blocks rather than doll legs, infant do not show any visual preference, even in the case of contingent tactile stimulation. A recent study by Filippetti et al. (2013) further showed that 1-to-4-day old newborns look longer towards a video displaying a paintbrush stroking an infant's cheek in synchrony with a tactile stimulation on their own cheek, than towards a video in which the stroke was asynchronous. Newborns show such a preference only when the observed face is depicted in its canonical upright orientation, but not when it is inverted [26] . The ability to detect intersensory synchrony is seen as crucial in the development of an early sense of one's own body. In fact, the early ability to match the rhythm of a corporeal sensory event to a non-corporeal one provides infants with critical information fundamental to perceive their own body as a differentiated object among other objects in the world [32] . Unlike cross-modal visual-tactile capabilities, so far infants' ability to recognize tactile stimulations on others' body solely based on visual information has not been investigated. Rather, research has focused on infants' visual perception of goal-directed movements [33, 34, 35, 36] showing that from the earliest stages of postnatal life newborns are able to discriminate between visual cues indicating goal-directed and non-goal-directed actions, and prefer the former to the latter [37] . Although it is clear that young infants detect goal-directed hand gestures, it is still unknown whether and at which stage of development they can visually recognize hand gestures depicting touch. Seeing Touches Early in Life PLOS ONE |
doi:10.1371/journal.pone.0134549 pmid:26366563 pmcid:PMC4569186 fatcat:zmzifhdgdrgldcyfovodvm7s74