Objective: The purpose of this study was to investigate the combined lexical effects of word frequency and neighborhood density (acoustic-phonetic similarity) on the recognition of words spoken in isolation and words spoken in sentences for children with normal hearing and children with cochlear implants.
Design: Lexically controlled sentences were created from a subset of words obtained from the spoken vocabulary of children between the ages of 3 and 5 yr. Two sentence lists were generated, applying the definitions and procedures of Kirk, Pisoni, and Osberger (1995) in accordance with the Neighborhood Activation Model ( Luce, 1986; Luce & Pisoni, 1998). One list was composed of lexically "easy" words (those high in frequency of occurrence but phonemically dissimilar to other words) and the other list was composed of lexically "hard" words (those low in frequency of occurrence but phonemically similar to other words). Each list consisted of five practice and 20 test sentences that were syntactically correct but semantically neutral (low in predictability). Three key words were used in constructing each of the 5- to 7-word sentences, resulting in 15 practice and 60 key words per test list. In the first of three experiments, 48 normal-hearing children between the ages of 5 and 12 yr were asked to repeat the words and sentences at one of six presentation levels to establish performance-intensity functions. In the second experiment, 12 normal-hearing children between the ages of 5 and 14 yr repeated the words and sentences under spectrally degraded conditions. Twelve children with cochlear implants ages 5 to 14 yr repeated the unprocessed stimuli in a third experiment.
Results: The lexically easy stimuli were recognized with greater accuracy than the lexically hard stimuli for the children tested in all three experiments. Sentence scores were significantly higher than word scores for the normal-hearing children (Experiments 1 and 2) and nine high-performing children with cochlear implants (Experiment 3). Word scores were higher than sentence scores for the three low-performing children with cochlear implants. There was a statistically significant relationship between chronological age and sentence score for the normal-hearing children listening under spectrally degraded conditions. For the children with cochlear implants, the relationship between language quotient and sentence and word scores was statistically significant.
Conclusion: Sensitivity to the combined lexical properties of word frequency and neighborhood density was evident both for words and sentences. Lexically easy stimuli were recognized with greater accuracy than lexically hard stimuli across groups, affirming the robustness of this effect and verifying that words were being organized in relation to the frequency and acoustic-phonetic properties of other words. Syntactic context facilitated word recognition for the children with normal hearing and the high-performing implant group. The three low-performing children with cochlear implants recognized words more accurately than sentences, reflecting limitations in linguistic and cognitive capacity.