Affective touch in infancy

Social touch is ubiquitous in caregiver-infant interactions. Research on animal models and preterm human infants has shown that touch is critical for a young organism’s physical and psychological growth. However, the role that social interaction through touch plays in the development of typically developing human infants is poorly understood. The research presented in this thesis investigated neural specialization for social touch and the mechanisms through which social touch might promote early development. I focus on a particular type of touch, slow velocity stroking, shown to activate a particular type of skin fibers in human adults, the CT-fibers, and to elicit affective responses (henceforth affective touch). Research presented here investigated cortical activation and autonomic responses to affective touch, during the first year of life. Firstly, in experiments 1 through 4 functional Near Infrared Spectroscopy (fNIRS) was employed to measure haemodynamic responses to affective and non-affective touch over inferior frontal and temporal cortices. Experiments 1, 2 and 3 used three different non-affective stimuli and revealed that specialization to affective touch in key nodes of the social brain has not developed yet in 5 to 7-months-old infants. Results from Experiment 4 suggest that this specialization emerges near the end of the first year of life (10-montholds). Secondly, in experiments 5 and 6 heart rate changes to affective and nonaffective touch were measured in three different age-groups (2, 7 and 9-monthold). Results revealed that infants in neither group displayed differential responses to the touch stimuli. Further, experiment 5 explored whether affective touch modulates visual attention but an effect was not found. Taken together these findings showed that preferential processing of affective touch is not evident during early development, at least when investigating neural and autonomic responses. In all my studies, I strived to present tactile stimuli in the absence of other social cues, thus ensuring that any effects would have been specific to touch. In the final discussion I suggest that the lack of context might have prevented infants from identifying affective touch. I also discuss the possibility that other forms of inter-personal touch, and not CT-targeted touch, may be critical in early human development, and should be investigated in future research

Neural plasticity and the limits of scientific knowledge

Western science claims to provide unique, objective information about the world. This is supported by the observation that peoples across cultures will agree upon a common description of the physical world. Further, the use of scientific instruments and mathematics is claimed to enable the objectification of science. In this work, carried out by reviewing the scientific literature, the above claims are disputed systematically by evaluating the definition of physical reality and the scientific method, showing that empiricism relies ultimately upon the human senses for the evaluation of scientific theories and that measuring instruments cannot replace the human sensory system. Nativist and constructivist theories of human sensory development are reviewed, and it is shown that nativist claims of core conceptual knowledge cannot be supported by the findings in the literature, which shows that perception does not simply arise from a process of maturation. Instead, sensory function requires a long process of learning through interactions with the environment. To more rigorously define physical reality and systematically evaluate the stability of perception, and thus the basis of empiricism, the development of the method of dimension analysis is reviewed. It is shown that this methodology, relied upon for the mathematical analysis of physical quantities, is itself based upon empiricism, and that all of physical reality can be described in terms of the three fundamental dimensions of mass, length and time. Hereafter the sensory modalities that inform us about these three dimensions are systematically evaluated. The following careful analysis of neuronal plasticity in these modalities shows that all the relevant senses acquire from the environment the capacity to apprehend physical reality. It is concluded that physical reality is acquired rather than given innately, and leads to the position that science cannot provide unique results. Rather, those it can provide are sufficient for a particular environmental setting