Electroencephalography and Eye-Tracking: Two Techniques Used to Measure Early Speech and Language Acquisition in Infants

The first years of life are foundational for developing cognitive abilities at later stages. One of these skills is the acquisition of the native language, which begins before birth. Despite its importance, measuring the processes that underlie speech and language acquisition using only behavioral methods is remarkably limited since infants' production is not related to their perceptual skills or the competence of their native language. To investigate speech and language acquisition at early ages, it is helpful to use a set of techniques to relate an objective measure with language and learning skills. For such purposes, numerous ethically and technically appropriate techniques for young children have been used, by which electroencephalography and eye-tracking stand out. Electroencephalography allows us to study the neural correlates of cognitive functions related to language acquisition through sound and visual stimuli. In the case of eye-tracking, it pursues the same objective but is associated with infants' ocular behavior. This article will review the most relevant aspects of electroencephalography and eye-tracking in infants to introduce researchers who begin to use these techniques in the study of young children.