Differences between early-developing and late-developing phonemes in phonological processing

Theoretical accounts of communication disorders often hinge on tasks with various confounds. The aim of this study was to challenge the assumption that children with specific language impairment (SLI) have deficits in phonological memory storage capacity solely because they perform poorly on nonword repetition tasks. This assumption was tested using a novel contrast of early- and late-developing phonemes that was predicted to elicit differences in nonword repetition performance even after controlling for confounding factors. Using a differential diagnosis model of testing, a variety of tasks were administered to determine if early vs. late phoneme differences (ELP) would persist after auditory perceptual, articulatory, phonological memory storage capacity, and lexical demands were minimized. In Study 1, 30 undergraduates completed nonword repetition, nonword reading, and auditory lexical decision tasks in which half of the stimuli contained only early-developing phonemes and half contained only later-developing phonemes. In Study 2, the ELP contrast was examined in another group of 20 undergraduates who completed auditory and visual lexical decision with and without concurrent articulation. Both nonword accuracy and word-nonword discriminability were consistently lower for items with later-developing phonemes than for those with early-developing phonemes, but there were no differences in response times. Results support the growing literature suggesting that nonword repetition relies on multiple processes and cannot be used as a measure of phonological memory storage capacity alone. Additionally, nonword repetition performance draws on skills apart from auditory perceptual demands, articulatory demands, and lexical knowledge. This in turn challenges the assumption that children with SLI have deficits in phonological memory storage capacity simply because they perform poorly on nonword repetition. The results may suggest that the ELP contrast reflects differences in the quality of the phonological representations that derive from the timing of phoneme acquisition, though other possible explanations for the differences are discussed (e.g., other articulatory influences). The ELP manipulation within this battery of tasks affords many possible outcomes that might adjudicate between the possible accounts of deficits that have been associated with SLI, such as perceptual and motor speech deficits that may each contribute independently or additively to poor performance in phonological processing