One of the most profound differences between hearing-impaired and normal-hearing children is the rate of vocabulary acquisition. Typically developing children with normal hearing can learn more than 2 new words per day and have a vocabulary of 4,000-5,000 words by age 5. This is in stark contrast to the child with significant hearing loss who may have a vocabulary as small as 500 words at age 5 (Bloom, 2000;Conrad, 1979). These deficits in vocabulary acquisition will impact development of higher level language abilities including syntax, word segmentation and ultimately reading comprehension. Understanding and ameliorating deficits in vocabulary size can not only lead to improved word recognition but can also accelerate the acquisition of other linguistic competencies that are essential for communicative and academic success.
Specific Aim 1 will determine the sensory, perceptual, and cognitive factors that mediate vocabulary acquisition in hearing impaired (50 children age 6-7 years with cochlear implants or digital hearing aids;50 normal hearing age mates will be compared on all measures). Hypotheses to be tested (D1.1-D1.3) are based on the idea that receptive vocabulary in hearing-impaired children requires the efficient operation and integration of sensory, perceptual, and cognitive abilities. Hearing impaired children's ability to perceive speech in every day environments (background noise and at all levels of speech from soft to loud) facilitates the child's ability to """"""""overhear"""""""" language and promotes increased receptive vocabulary size through novel word learning (implicit learning). The less proficient a child is in perceiving speech in demanding listening conditions the more difficulty he/she will exhibit retaining information in working memory. Shortened memory span will influence explicit verbal learning and contribute to delayed vocabulary acquisition as measured by receptive vocabulary size. Hypotheses (D2.1 &D2.2) for Specific Aim 2 will address the variability in rate of language growth in children that have received early identification and device use by obtaining longitudinal data examining the long-term effects of speech perception and developing cognitive skills on vocabulary size. This study will use an integrated multidisciplinary approach to examine the interaction between perceptual and cognitive mechanisms in understanding and improving the linguistic skills of hearing impaired children.
