Shedding Light on Language Function and Its Development with Optical Brain Imaging

Language can be described as a ubiquitous marvel: Nearly all humans acquire and process their native language(s) effortlessly. The neural bases of both acquisition and processing have long captured scientific attention. The study of the brain networks underlying language development, perception, and production was facilitated by the advent of functional near-infrared spectroscopy (fNIRS), which has led to a remarkable expansion of language studies, particularly on developing populations. This chapter introduces the technique, discussing the advantages and disadvantages relative to other common methods. It is argued that fNIRS provides an interesting compromise for the case of language studies in particular, given that it has a moderate spatial resolution, it is inexpensive and silent, and it is moderately tolerant of a range of movement. The chapter then turns to experimental design, instrumentation, and data analyses. In addition to laying out a number of potential options for each, it provides readers with useful practical advice, ranging from how to decide on the placement of optodes on the participant’s head to how to avoid data contamination due to muscular and other diverse artefacts. Next, the chapter provides a brief summary of three key strands of research in the study of language acquisition. In particular, it discusses the evidence for and against the presence of specific biases leading to left-dominant speech processing, the emergence of multi-region brain networks for language processing, and the use of fNIRS among clinical populations. It concludes by discussing likely advances in the near future of the technique.