Category learning with(out) language: congenital deafness as a critical test for the role of language input in early category learning

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When born into hearing families, profoundly deaf infants have little access to the language used in their homes. Cochlear implantation is now the most frequent intervention route, yet, despite surgery being offered as early as 9 months of age and improvements in the acoustics of implants, delays in language persist into childhood. Importantly, exposure to sign language prior to implantation benefits both later oral language and general cognitive development, but we have poor understanding of why this is the case. We propose to investigate a new hypothesis, that language input (verbal or signed), in the form of caregivers labelling the objects infants encounter, helps infants parse the world into categories such as cats or cars. This ability to categorize is a game changer for learning, including for vocabulary growth - recognising a new object as a car, a category we are familiar with, means that we can immediately infer what this object is called and that it moves very fast. We put forward an innovative research programme that will provide new understanding of the interaction between early language and conceptual development.1) We will break with classical lab-based category learning paradigms, which have underestimated the importance of language input, to investigate learning in more naturalistic environment. Unlike lab-based studies, where infants learn the category of cats, for example, by seeing various cats one after the other, on uncluttered backgrounds, in their daily lives, minutes, hours or days may pass between encountering different cats; memory decay and interference will make it difficult for infants to see what is common between the members of this category. Taking infants on a real or virtual Learning Trail in the Norwich Castle museum, we will ask whether being told what objects are called acts as a memory cue, helping category learning by reducing memory decay.2) We will develop new methodologies to quantify the category knowledge that children acquire in their daily lives. While a variety of methods exist to measure vocabulary growth, developmental sciences have as yet no means to measure the growth in children's conceptual knowledge. We will use electroencephalography and eye-tracking to chart the growth in category knowledge in the first two years of life, in hearing infants, which will serve as comparison for the study of deaf infants.3) We will provide, for the first time, the critical test for the role language input may have in category learning by measuring category knowledge in the absence of language, in a longitudinal cohort of deaf infants born into hearing families. Using a comprehensive set of measures of early conceptual and communicative development, we will be in a unique position to understand what causes the delays in language and learning in this population. This proposal brings together a unique team of researchers with complementary expertise in overseeing longitudinal cohort studies, brain imaging and early cognitive development in hearing and deaf children with professionals involved in clinical care and education of deaf infants. Working closely with audiologists and teachers for the deaf will ensure that research is driven by the needs of deaf infants and their families and, more importantly, that research findings feed-back into clinical practice (e.g. developing measures of category knowledge to be used as part of clinical assessments of deaf infants), as well as in early education (e.g. revealing alternative, non-linguistic strategies caregivers could use to scaffold infants' conceptual development as part of low burden high impact parent-mediated interventions). Our close collaboration with Norwich Castle Museum Early Years Team will transform the delivery of inclusive museum early education - e.g. by developing ways to engage children with categories rather than isolated exemplars to ensure that learning about historical artefacts generalises beyond the museum's gates.