Background-The non-word repetition task (NRT) has gained wide acceptance in describing language acquisition in both children with normal language development (NL) and children with specific language impairments (SLI). This task has gained wide acceptance because it so closely matches the phonological component of word learning, and correlates with measures of phonological working memory, a deficit in which is hypothesized to underlie SLI.

Purpose-This study investigated lexical representations of children with specific language impairment (SLI) and typically developing, chronological age-matched (CA) peers on a frequency-manipulated gating task. The study tested the hypothesis that children with SLI have holistic phonological representations of words, that is, that children with SLI would exhibit smaller effects of neighborhood density on gating durations than CA peers and that children with SLI would be as efficient as CA peers in accessing high-frequency words but that they would differ from their age-matched peers in accessing low-frequency words.Method-Thirty-two children (ages 8;5-12;3 [years;months]) participated: 16 children with SLI and 16 typically developing peers matched on age and nonverbal IQ. Children's word guesses after different gating durations were investigated.Results-Contrary to predictions, no group differences in effects of distributional regularity were found: Children in both groups required equally longer acoustic chunks to access words that were low in frequency and came from dense neighborhoods. However, children with SLI appeared to vacillate between multiple word candidates at significantly later gates when compared with children in the CA group.Conclusions-Children with SLI did not exhibit evidence for phonologically holistic lexical representations. Instead, they appeared more vulnerable to competing words. Keywords SLI; lexical representation; word frequency; neighborhood densityThis study investigated lexical access in children with specific language impairment (SLI) and typically developing peers on a frequency-manipulated forward gating task. Specific language impairment refers to a developmental condition in which children exhibit difficulty acquiring language in the absence of other neurodevelopmental, frankContact author: Elina Mainela-Arnold, Department of Communication Sciences and Disorders, Pennsylvania State University, 401K Ford Building, University Park, PA 16802-3100. ezm3@psu.edu. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript neurological, hearing, emotional, or nonverbal intellectual impairments (Leonard, 1998;Tomblin, Records, & Zhang, 1996). Clinically, delayed onset of lexical acquisition is, in most cases, the first indication of SLI, and children with SLI can be differentiated from their typically developing peers on the basis of estimates of vocabulary size, standardized vocabulary tests, and the number of different words produced in spontaneous language samples (Bishop, 1997;Watkins, Kelly, Harbers, & Hollis, 1995).Lexical processes have been shown to be compromised in SLI in many experimental studies. Children with SLI exhibit slower speeds of lexical processing as compared with their peers. They exhibit slower speed of naming Leonard, Nippold, Kail, & Hale, 1983) and slower reaction times in word recognition experiments . Children with SLI also make naming errors, both phonological errors (Lahey & Edwards, 1999) and semantic errors (McGreg...

A series of three experiments examined children's sensitivity to probabilistic phonotactic structure as reflected in the relative frequencies with which speech sounds occur and co-occur in American English. Children, ages 212 and 312 years, participated in a nonword repetition task that examined their sensitivity to the frequency of individual phonetic segments and to the frequency of combinations of segments. After partialling out ease of articulation and lexical variables, both groups of children repeated higher phonotactic frequency nonwords more accurately than they did low phonotactic frequency nonwords, suggesting sensitivity to phoneme frequency. In addition, sensitivity to individual phonetic segments increased with age. Finally, older children, but not younger children, were sensitive to the frequency of larger (diphone) units. These results suggest not only that young children are sensitive to fine-grained acoustic-phonetic information in the developing lexicon but also that sensitivity to all aspects of the sound structure increases over development. Implications for the acoustic nature of both developing and mature lexical representations are discussed.

Structural analyses of developing lexicons have provided evidence for both children's holistic lexical representations and sensitivity to phonetic segments. In the present investigation, neighbourhood analyses of two children's (age 3;6) expressive lexicons, maternal input, and an adult lexicon were conducted. In addition to raw counts and frequency-weighted counts, neighbourhood size was calculated as the proportion of the lexicon to which each target word is similar, to normalize for vocabulary size differences. These analyses revealed that children's lexicons contain more similar sounding words than previous analyses indicated. Further, neighbourhoods appear denser earlier in development relative to vocabulary size, presumably because children first learn words with more frequent sounds and sound combinations. Neighbourhood density as a proportion of the size of the lexicon then decreases over development as children acquire words with less frequent sounds and sound combinations. These findings suggest that positing fundamentally different lexical representations for children may be premature.

Perceptual systems in all modalities are predominantly sensitive to stimulus change, and many examples of perceptual systems responding to change can be portrayed as instances of enhancing contrast. Multiple findings from perception experiments serve as evidence for spectral contrast explaining fundamental aspects of perception of coarticulated speech, and these findings are consistent with a broad array of known psychoacoustic and neurophysiological phenomena. Beyond coarticulation, important characteristics of speech perception that extend across broader spectral and temporal ranges may best be accounted for by the constant calibration of perceptual systems to maximize sensitivity to change. Sensorineural systems respond to changeIt is both true and fortunate that sensorineural systems respond to change and to little else. Perceptual systems do not record absolute level be it loudness, pitch, brightness, or color. This fact has been demonstrated in every sensory domain. Physiologically, sensory encoding is always relative. This sacrifice of absolute encoding has enormous benefits along the way to maximizing information transmission. Biological sensors have impressive dynamic range given their evolution via borrowed parts (e.g., gill arches becoming middle ear bones). However, biological dynamic range always is a small fraction of the physical range of absolute levels available in the environment as well as in the perceptual range essential to organisms' survival. This is true whether one is considering optical luminance or acoustic pressure. The beauty of sensory systems is that, by responding to relative change, a limited dynamic range adjusts to maximize the amount of change that can be detected in the environment.The simplest way that sensory systems adjust dynamic range to maximize sensitivity to change is via adaptation. Following nothing, a sensory stimulus triggers a strong sensation. However, when sustained sensory input does not change over time, constant stimulation loses impact. This sort of sensory attenuation due to adaptation is ubiquitous, and has been documented in vision (Riggs et al