How we stumbled upon the rat play vocalizations: A recollection.

The introduction of universal newborn hearing screening (UNHS) has resulted in increased rates of early-identified unilateral hearing loss (UHL; ; ) and a subsequent increase in early device fitting (). While compelling evidence exists to support early device fitting (; ; ; ; ), and consistent device use for children with bilateral hearing loss to improve developmental outcomes (; ), this is not the case for children with UHL (; ). In the absence of such evidence, clinicians find it challenging to support families in making informed decisions around device fitting (; ; ). With the goal of increasing evidence regarding early device fitting for young children with UHL, the purpose of this study was to evaluate the nature of associations between linguistic input and communication outcomes and the impact of consistency of device use on such associations. While UHL has been evidenced to adversely affect language outcomes (; ), the reasons for this are unknown (). One hypothesis for language difficulties in this population is that access to sufficient quantity of linguistic input (the number of words and utterances in a child’s environment; ) may be compromised due to decreased audibility, poorer functional listening (), absence of, or diminished binaural function which impairs sound localisation (), and/or increased difficulties in understanding speech in adverse acoustics like noise (). This may in turn impact incidental language learning, especially in challenging listening environments (; ). Device fitting in children with UHL may improve sound localisation (cochlear implants; ; hearing aids; ) and speech recognition in noise (cochlear implants; ; ; bone anchored hearing aids; ), and consistent device use is associated with higher speech recognition scores (cochlear implants; ). While benefits of device fitting have been evidenced for this population, whether or not fitting and consistent device use enhances access to linguistic input sufficiently to influence communication outcomes remains unknown. It is well-established that for all children, direct and incidental exposure to linguistic input during the early years of life is imperative for language development (; ; ). Exposure to linguistic input occurs through daily caregiver-child interactions and can be captured for analysis via tools such as the Language ENvironment Analysis (LENA) system (). The LENA system measures two linguistic input quantity metrics, conversational turn count (CTC) and adult word count (AWC). CTC measures the total number of conversational exchanges (initiation and response within 5 seconds) between the child (wearing the LENA recorder) and an adult. AWC is the total number of words spoken by adults in proximity, but not necessarily to the child (). In addition to measures that profile the quantity of linguistic input, the LENA provides estimates of the number of vocalisations produced by the child. LENA metrics such as CTC, AWC and child vocalisations are positively correlated with language outcomes in children with typical hearing (; ).