Adults' perception and production of the English vowel /i/.

This study investigated the link between the perception and production of the English vowel /i/ by adult native speakers of English. Participants first produced the vowel /i/ using normal (citation) and careful (hyperarticulated) speech, then completed a method of adjustment task in which they selected their ideal exemplar of /i/. In this perceptual task, 24 of 35 participants had a prototype; the remaining 11 did not, but were retained for comparison. In keeping with the hyperspace effect (K. Johnson, E. Flemming, & R. Wright, 1993), all participants selected perceptual stimuli with F1 and F2 values that were more extreme (i.e., higher and further forward in the vowel space) than those of their normal, citation productions. An analysis of front-back and high-low qualities for the perceptual and production data in Euclidian space revealed that hyperarticulated speech was closer to the perceptual data than citation speech was, but only for participants with relatively clear-cut prototypes. The basis for such individual variation in perception-production links is discussed.

Adults' perception of native and nonnative vowels: implications for the perceptual magnet effect.

Two experiments were conducted to evaluate the perceptual magnet effect. In Experiment 1, American English speakers representing diverse dialects were presented with a fine-grained set of stimuli (varying in just noticeable differences for F1 and F2) and indicated whether they heard "/i/" or "not/i/," thus delimiting the /i/ portion of the vowel space for individual subjects. Then these same subjects selected their own /i/ prototype with a method-of-adjustment procedure. The data from this experiment were used to synthesize customized prototype and nonprototype stimulus sets for Experiment 2. In Experiment 2, 24 of our original 37 subjects completed a discrimination task for each of three conditions, in which vector stimuli varied from the subject's prototype, the nonprototype, or a foreign vowel (/y/) in 15-mel steps. Subjects displayed higher discrimination, as indexed by d', for the nonprototype condition than they did for both the prototype and the foreign conditions. In addition, discrimination was better for variants further away from the referent in each condition. However, discrimination was not especially poor for stimuli close to subjects' individual prototypes--a result that would have yielded the strongest support for the operation of a magnet effect. This negative finding, together with other aspects of our results, raises problems for any theory of vowel perception that relies solely on "one-size-fits-all" prototype representations.

Effects of age and Alzheimer's disease on recognition of gated spoken words.

This study investigated the effects of normal aging and Alzheimer's disease on listeners' ability to recognize gated spoken words. Groups of healthy young adults, healthy older adults, and adults with Alzheimer's disease were presented isolated gated spoken words. Theoretical predictions of the Cohort model of spoken word recognition (Marslen-Wilson, 1984) were tested, employing both between-group and within-group comparisons. The findings for the young adults supported the Cohort model's predictions. The findings for the older adult groups revealed different effects for age and disease. These results are interpreted in relation to the theoretical predictions, the findings of previous gating studies, and differentiating age from disease-related changes in spoken word recognition.

The gating paradigm: effects of presentation format on spoken word recognition by children and adults.

This study focused on the impact of stimulus presentation format in the gating paradigm with age. Two presentation formats were employed--the standard, successive format and a duration-blocked one, in which gates from word onset were blocked by duration (i.e., gates for the same word were not temporally adjacent). In Experiment 1, the effect of presentation format on adults' recognition was assessed as a function of response format (written vs. oral). In Experiment 2, the effect of presentation format on kindergarteners', first graders', and adults' recognition was assessed with an oral response format only. Performance was typically poorer for the successive format than for the duration-blocked one. The role of response perseveration and negative feedback in producing this effect is considered, as is the effect of word frequency and cohort size on recognition. Although the successive format yields a conservative picture of recognition, presentation format did not have a markedly different effect across the three age levels studied. Thus, the gating paradigm would seem to be an appropriate one for making developmental comparisons of spoken word recognition.

Young children's age-of-acquisition estimates for spoken words.

This study was concerned with the impact of stimulus familiarity on young children's ability to recognize spoken words and make explicit judgments about them. In Experiment 1, 5-year-olds made age-of-acquisition (AOA) estimates for a set of words that were very similar to estimates made by older children and adults. In Experiment 2, young children's picture recognition, mispronunciation detection, and vocabulary monitoring performance all varied systematically with these AOA estimates and with a stimulus-type (intact-mispronounced) manipulation. Subjective AOA estimates (whether from children or from adults) proved to be a better predictor of performance than did two objective familiarity measures and subjective imageability. These results point to considerable metalexical knowledge on the part of young children or explicit sensitivity regarding their own vocabulary knowledge. In addition, the results lend some support to the notion that actual AOA contributes to subjective AOA estimates.

The growth of lexical constraints on spoken word recognition.

In this study, we examined the influence of various sources of constraint on spoken word recognition in a mispronunciation-detection task. Five- and 8-year-olds and adults were presented with words (intact or with word-initial or noninitial errors) from three different age-of-acquisition categories. "Intact" and "mispronounced" responses were collected for isolated words with or without a picture referent (Experiment 1) and for words in constraining or unconstraining sentences (Experiment 2). Some evidence for differential attention to word-initial as opposed to noninitial acoustic-phonetic information (and thus the influence of sequential lexical constraints on recognition) was apparent in young children's and adults' response criteria and in older children's and adults' reaction times. A more marked finding, however, was the variation in subjects' performance, according to several measures, with age and lexical familiarity (defined according to adults' subjective age-of-acquisition estimates). Children's strategies for responding to familiar and unfamiliar words in different contexts are discussed.

Infant discrimination of two- and five-formant voiced stop consonants differing in place of articulation.

According to recent theoretical accounts of place of articulation perception, global, invariant properties of the stop CV syllable onset spectrum serve as primary, innate cues to place of articulation, whereas contextually variable formant transitions constitute secondary, learned cues. By this view, one might expect that young infants would find the discrimination of place of articulation contrasts signaled by formant transition differences more difficult than those cued by gross spectral differences. Using an operant head-turning paradigm, we found that 6-month-old infants were able to discriminate two-formant stimuli contrasting in place of articulation as well as they did five-formant + burst stimuli. Apparently, neither the global properties of the onset spectrum nor simply the additional acoustic information contained in the five-formant + burst stimuli afford the infant any advantage in the discrimination task. Rather, formant transition information provides a sufficient basis for discriminating place of articulation differences.

Onset spectra and formant transitions in the adult's and child's perception of place of articulation in stop consonants.

Stevens and Blumstein [Perspectives on the Study of Speech (Erlbaum, Hillsdale, NJ, 1981)] have proposed that the global shape of the CV syllable onset spectrum provides the listener with a primary and contextually invariant cue for place of stop consonant articulation. Contextually variable formant transitions are, in contrast, claimed to constitute secondary cues to place of articulation that, during development, are learned through their co-occurrence with the primary spectral ones. In the two experiments reported here, these claims about the relative importance of the onset spectrum and formant transition information were assessed by obtaining adults' and young children's identifications of synthetic stimuli in which these two potential cues specified different places of articulation. In general, the responses of both adults and children appeared to be determined by the formant transitions of the stimuli. These results provide little support for the claim that sensitivity to the global properties of the onset spectrum (as described by Stevens and Blumstein) underlie place of articulation perception or for Stevens and Blumstein's primary versus secondary cue distinction. Rather, these findings are consistent with the view that dynamic, time-varying information is important in the perception of place of articulation.