Observational measures of caregiver's touch behavior in infancy: A systematic review.

The caregiver's touch behavior during early infancy is linked to multiple developmental outcomes. However, social touch remains a challenging construct to operationalize, and although observational tools have been a gold standard for measuring touch in caregiver-infant interactions, no systematic review has been conducted before. We followed the PRISMA guidelines and reviewed the literature to describe and classify the main characteristics of the available observational instruments. Of the 3042 publications found, we selected 45 that included an observational measure, and from those we identified 12 instruments. Most of the studies were of infants younger than six months of age and assessed touch in two laboratory tasks: face-to-face interaction and still-face procedure. We identified three approaches for evaluating the caregiver's touch behavior: strictly behavioral (the observable touch behavior), functional (the functional role of the touch behavior), or mixed (a combination of the previous two). Half of the instruments were classified as functional, 25% as strictly observational, and 25% as mixed. The lack of conceptual and operational uniformity and consistency between instruments is discussed.

Three Months-Old' Preferences for Biological Motion Configuration and Its Subsequent Decline.

To perceive, identify and understand the action of others, it is essential to perceptually organize individual and local moving body parts (such as limbs) into the whole configuration of a human body in action. Configural processing-processing the relations among features or parts of a stimulus-is a fundamental ability in the perception of several important social stimuli, such as faces or biological motion. Despite this, we know very little about how human infants develop the ability to perceive and prefer configural relations in biological motion. We present two preferential looking experiments (one cross-sectional and one longitudinal) measuring infants' preferential attention between a coherent motion configuration of a person walking vs. a scrambled point-light walker (i.e., a stimulus in which all configural relations were removed, thus, in which the perception of a person is impossible). We found that three-month-old infants prefer a coherent point-light walker in relation to a scrambled display, but both five- and seven-month-old infants do not show any preference. We discuss our findings in terms of the different perceptual, attentional, motor, and brain processes available at each age group, and how they dynamically interact with selective attention toward the coherent and socially relevant motion of a person walking during our first year of life.

Right STS responses to biological motion in infancy - An fNIRS study using point-light walkers.

Biological motion perception-our capacity to perceive the intrinsic motion of humans and animals-has been implicated as a precursor of social development in infancy. In the adult brain, several biological motion neural correlates have been identified; of particular importance, the right posterior superior temporal sulcus (rpSTS). We present a study, conducted with fNIRS, which measured brain activations in infants' right posterior temporal region to point-light walkers, a standard stimulus category of biological motion perception studies. Seven-month-old infants (n = 23) participated in a within-subject blocked design with three experimental conditions and one baseline. Infants viewed: an intact upright point-light walker of a person approaching the observer; the same point-light walker stimulus but inverted; and a selected frame from the point-light walker stimulus, approaching the viewer at constant velocity with no articulated motion, close to object motion. We found activations for both the upright and the inverted point-light walkers. The rigid moving point-light walker frame did not elicit any response consistent with a functional activation in this region. Our results suggest that biological motion is processed differently in the right middle posterior temporal cortex in infancy, and that articulated motion is a critical feature in biological motion processing at this early age.

Infants' cortical processing of biological motion configuration - A fNIRS study.

Biological motion perception is a key component of action perception contributing to social cognition in crucial ways. Contemporary neuroimaging studies show that biological motion is processed differently in the human brain from other types of motion. In particular, the right posterior Superior Temporal Sulcus (rpSTS), an area known for its central role in social perception, has been consistently associated with the perception of biological motion in the mature brain. By contrast, most findings investigating the development of biological motion perception in infancy come from behavioral studies, and far less is known regarding the right STS' role in processing biological motion. The current study used fNIRS to measure brain activation to biological motion in the rSTS region of 7-8-month-old infants. Infants were presented with two conditions: an approaching coherent motion of a person walking (coherent point-light-walker, PLW); and a spatially scrambled version of this display, where the global configuration of a person walking was disrupted (scrambled PLW). We found a functional activation, i.e., a significant increase in HbO2 concentration in relation to baseline, in the right middle-posterior temporal cortex only when infants viewed the coherent point-light-walker. This activation statistically differed from the scrambled point-light-walker, and no significant activations were found for viewing the scrambled motion. Our study adds evidence pointing to rSTS' sensitivity to the global human configuration in biological motion processing during infancy. The rSTS seems thus to become functionally specialized in biological motion configuration as early as at 7-8 months of age.

Brain mechanisms for processing discriminative and affective touch in 7-month-old infants.

Affective touch has been associated with affiliative behavior during early stages of infant development; however, its underlying brain mechanisms are still poorly understood. This study used fNIRS (functional near-infrared spectroscopy) to examine both affective and discriminative touch in 7- month-old infants (n=35). Infants were provided affective stimuli on the forearm for 10 sec followed by a 20 sec rest period. The protocol was repeated for discriminative touch, and both affective and discriminative stimuli were given in a counterbalanced order. Brain activation (oxy-hemoglobin and deoxy-hemoglobin levels) in the somatosensory and temporal regions was registered during administration of the stimuli. There was an increase in oxy-hemoglobin and decrease in deoxy-hemoglobin only in the somatosensory region in response to both affective and discriminative touch. No other activations were found. Seven-month-old infants' brain activation in the somatosensory cortex was similar for both discriminative and affective touch, but the stimuli did not elicit any activation in the temporal region/ pSTS. Our study is the first to suggest that 7-month-old infants do not yet recruit socio-emotional brain areas in response to affective touch.