Effects of semantic predictability on children's preservation of a phonemic voice contrast.

We investigated the effects of semantic predictability on children's preservation of the /t/-/d/ phonemic voice contrast in American English. In Experiment 1, a total of 36 seven-, nine-, and twelve-year-olds produced minimal pairs differing in intervocalic /t/ and /d/ in semantically biasing and semantically neutral passages. The seven-year-olds preserved the phonemic contrast in both passage types. However, for the nine- and twelve-year-olds, total word duration and preceding vowel duration preserved the /t/-/d/ contrast, but this interacted with semantic predictability. The contrast was preserved in the biasing and not in the neutral passages. The production results from the older children replicated previous findings from adults, demonstrating that semantic predictability influences speech production at both a lexical and a segmental level. In Experiment 2, listeners identified the tokens produced in Experiment 1. The identification results suggested that differences produced by speakers may not necessarily have a functional role for listeners. An interactive activation framework is proposed to account for the semantic effects on older children's and adults' production. For the youngest children, however, we suggest that pragmatic compensation and task demands interact with the effects of interactive activation.

The effects of semantic predictability in non-pathological older adults' production of a phonemic contrast.

The present study examined the effects of semantic predictability in non-pathological older adults' production of the /t/-/d/ phonemic voice contrast. Experiment 1 examined young and older adults' production of /t/ and /d/ words embedded in semantically biasing and neutral passages and when produced in the clear or in noise. Experiment 2 assessed the perceptual intelligibility of subjects' production by examining listeners' identification of the /t/-/d/ words produced in Experiment 1. The results replicate previous findings demonstrating that duration lengthens in neutral vs. biasing contexts. However, the results also show agerelated differences. Older adults preserved the /t/-/d/ contrast in all the experimental manipulations; young adults were more variable. In addition, listeners were better able to identify the words produced by the older adults. We suggest that older adults compensate pragmatically for their cognitive inability to integrate and process the semantic information in the neutral contexts. Consequently, they adopt a strategy for all passages and hyperarticulate the /t/-/d/ contrast in an attempt to ensure successful communication. It is believed that these results contribute to the understanding of the normal ageing process in speech production, and may help identify differences between normal life-span developments and pathological deviations during communication.

Cognitive factors involved in preserving a phonemic contrast.

Previous research has demonstrated that semantics and pragmatics influence durational modifications in words and segments. The present research investigated specifically how semantics and pragmatics influence preservation of a phonemic contrast. Experiment 1 examined alveolar flapping in American English. Potentially flapped words, for example, writer and rider, were embedded in each of two types of semantic passages: semantically biasing and semantically neutral passages. In addition, these passages were produced in one of two pragmatic conditions: listener-present and listener-absent. The results showed that the phonemic voicing distinction between /t/ and /d/ was preserved in biasing passages and in the listener-present condition. The /t/-/d/ distinction was not preserved in neutral passages or in the listener-absent condition. Experiment 2 examined whether listeners could use the durational differences found to distinguish phonemic voicing in Experiment 1. Our investigation demonstrates that semantics and pragmatics interact with phonological processes in speech production. We speculate that phonological processes may be affected both by speakers' decision processes to adjust their articulation for the benefit of the listener and by speakers' internal structure and interactive activation among linguistic units.

Phonotactics and syllable stress: implications for the processing of spoken nonsense words.

Two experiments using bisyllabic CVCCVC nonsense words that varied in phonotactic probability and stress placement were conducted to examine the influences of phonotactic and metrical information on spoken word recognition. Experiment 1 examined participants' intuitions about the phonological "goodness" of nonsense words. Experiment 2 examined processing times for the same stimuli in a speeded auditory repetition task. The results of both studies provide further evidence that the phonotactic configuration and stress placement of spoken stimuli have important implications for the representation and processing of spoken words.

Infants' sensitivity to word boundaries in fluent speech.

Infants' sensitivity to word units in fluent speech was examined by inserting I sec pauses either at boundaries between successive words (Coincident versions) or between syllables within words (Noncoincident versions). In Experiment 1, 24 11-month-olds listened significantly longer to the Coincident versions. In Experiment 2, 24 four-and-a-half- and 24 nine-month-olds did not exhibit the preference for the Coincident versions that the 11-month-olds showed. When the stimuli were low-pass filtered in Experiment 3, 24 11-month-olds showed no preference for the Coincident versions, suggesting they rely on more than prosodic cues. New stimulus materials in Experiment 4 indicated that responses by 24 11-month-olds to the Coincident and Noncoindent versions did not depend solely on prior familiarity with the targets. Two groups of 30 11-month-olds tested in Experiment 5 were as sensitive to groups of 30 11-month-olds tested in Experiment 5 were as sensitive to boundaries for Strong/Weak words as for Weak/Strong words. Taken together, the results suggest that, by 11 months, infants are sensitive to word boundaries in fluent speech, and that this sensitivity depends on more than just prosodic information or prior knowledge of the words.

An examination of similarity neighbourhoods in young children's receptive vocabularies.

Based on an analysis of similarity neighbourhoods of worlds in children's lexicons, Dollaghan (1994) argues that because of the degree of phonological overlap among lexical items in memory, children must perform detailed acoustic-phonetic analyses in order to recognize spoken words. This is in contradiction to Charles-Luce & Luce (1990), who reported that the similarity neighbourhoods in younger children's expressive lexicons are sparse relative to older children's and adult lexicons and that young children may be able to use more global word recognition strategies. The current investigation re-examined these issues. Similarity neighbourhoods of young children's receptive vocabularies were analysed for three-phoneme, four-phoneme and five-phoneme words. The pattern of the original results from Charles-Luce & Luce (1990) was replicated.

The effects of semantic context on voicing neutralization.

The present study examined regressive voice assimilation in Catalan in an attempt to determine a systematic explanation of complete versus incomplete voicing neutralization. Two types of contexts were constructed. In one type, semantic information was present to bias the meaning of target words. In the other type, no semantic information was present. The results showed that vowel duration distinguished underlying voicing in the neutral context only. The results suggest that neutralization occurs when semantic information is present, but that a voicing contrast is realized when it is absent.

Similarity neighbourhoods of words in young children's lexicons.

Similarity neighbourhoods for words in young children's lexicons were investigated using three computerized databases. These databases were representative of three groups of native English speakers: 5-year-olds, 7-year-olds, and adults. Computations relating to the similarity neighbourhoods of words in the children's and adult's lexicon revealed that words in the 5- and 7-year-olds' lexicons have many fewer similar neighbours than the same words analyzed in the adult lexicon. Thus, young children may employ more global recognition strategies because words are more discriminable in memory. The neighbourhood analyses provide a number of insights into the processes of auditory word recognition in children and the possible structural organization of words in the young child's mental lexicon.

Contextual effects on vowel duration, closure duration, and the consonant/vowel ratio in speech production.

Acoustic measurements were conducted to determine the degree to which vowel duration, closure duration, and their ratio distinguish voicing of word-final stop consonants across variations in sentential and phonetic environments. Subjects read CVC test words containing three different vowels and ending in stops of three different places of articulation. The test words were produced either in nonphrase-final or phrase-final position and in several local phonetic environments within each of these sentence positions. Our measurements revealed that vowel duration most consistently distinguished voicing categories for the test words. Closure duration failed to consistently distinguish voicing categories across the contextual variables manipulated, as did the ratio of closure and vowel duration. Our results suggest that vowel duration is the most reliable correlate of voicing for word-final stops in connected speech.