With the increasing prevalence of autism diagnoses globally, the overall aim of this dissertation is to improve our understanding of the linguistic aptitude of autistic individuals. Given that the autism diagnosis is a spectrum, we rely on the Autism Quotient (AQ) test, which measures the quantity of autistic-like traits an individual possesses, to provide a quantitative value for the diagnosis. The goal of this study is to better understand how autistic-like traits may affect a child’s phonological abilities at the segment-level, measured by their ability to imitate voice onset time (VOT) when producing stop consonants of a novel second language (L2).

Our participants are both typically-developing (TD) and neurodiverse children, all 18 of whom are English-dominant children ages seven to 11 years old based in New South Wales, Australia. The methodology includes a parent survey completed on behalf of the child and experimental tasks, completed in person by the child, across two sessions that were separated by four to seven days. The experimental tasks consist of both English and Spanish read-aloud tasks, as well as Spanish immediate imitation tasks, and perception tasks featuring manipulated syllables spanning the full range of Spanish and English stop consonant VOT values. These tasks allow us to evaluate how well the participants imitate and learn to produce Spanish words with the appropriate, shortened VOT values.

Since individuals with higher AQ scores have more autistic-like traits, such as greater attention to detail and focus, we predict these individuals will be better L2 phonetic learners. The results show that autistic-like traits are not predictive of a child’s L2 phonetic imitation, nor short-term or long-term L2 phonetic learning abilities. That being said, regardless of diagnosis, our participants show a significant VOT reduction on the L2 phonetic imitation task and they learn to maintain a reduced VOT when producing Spanish word-initial stops, in both the short-term and the long-term. All of the children in the present study are capable L2 phonetic imitators and learners; thus, we encourage L2 learning in classrooms to offer an additional communicative outlet and improve children’s social skills, neurodivergent or not.

This dissertation investigates the development of cross-linguistic transfer in the use of strategies to repair preconsonantal word-external empty onsets (i.e., /C#V/) in Spanish heritage speakers. The main focus of this work is to analyze the use of /ʔ/-epenthesis as a strategy to repair empty onsets, as its use is asymmetrical in the Spanish and English phonologies.

A total of 190 participants (i.e., monolingually raised Spanish speakers, monolingually raised English speakers and Spanish heritage speakers) took part in Spanish and/or English word production tasks that elicited function + content word sequences in real words (e.g., Sp. un elefante 'an elephant', En. an umbrella) and in phonotactically legal novel words (e.g., Sp. un anbo, En. all embos). Participants are divided in three main age groups: younger children, older children, and adults.

First, I examine whether the use of glottal phonation is a repair strategy employed more often in English than in Spanish, and whether it is conditioned by age. Overall, I find that in English glottal phonation is the preferred strategy to repair prosodically-prominent onsetless syllables, whereas, in Spanish, the preferred repair strategy is modal phonation in both prosodically and non-prosodically prominent syllables. For the Spanish real words, I find no effects of language development in the experiments with real words. In the experiment with novel words, I show that older children and adult children produce a greater rate of glottal phonation than younger children, which I explain as an effect of the unpredictability of the novel words in the context. In English, the rate of glottal phonation in the real words is not affected by age. For the English novel words, older children produce greater rates of glottal phonation than the adults, demonstrating a U-shaped behavior during language development.

Next, I formalize the Spanish and English results using MaxEnt grammars and accounting for three repair strategies: /ʔ/-epenthesis, no repair (i.e., coda consonant), and resyllabification/ambisyllabicity. I introduce the effect of prosodic prominence in the grammars using constraints on phonological enhancement.

I then compare the results of the Spanish heritage speakers to those of the monolingually raised Spanish and English speakers. For the Spanish real and novel words, I find that the younger and older child HS produce greater rates of glottal phonation than the monolingually raised Spanish speakers, but no significant difference is observed between the adult monolingually raised Spanish speakers and the adult heritage speakers. To account for these results, I claim that child heritage grammars are more permeable to cross-linguistic transfer than adult heritage grammars. In addition, in the Spanish real words, my results show that heritage speakers with a higher amount of Spanish output glottalize less often than heritage speakers with a low amount of Spanish output, which brings to the forefront the importance of language use to control transfer from the majority language. In English, my results show that, overall, heritage speakers produce lower rates of glottal phonation than monolingually-raised English speakers (i.e., the dominant language may also suffer from negative transfer from the heritage language).

Finally, I argue that the results for the heritage grammars can be formalized using a model of language coactivation during input evaluation � la Goldrick et al. (2016). The two sets of language-specific constraints are scaled by the speaker-specific activation scores, which set the intended language and reflect the speaker's language dominance. To account for the apparent development of language control during language maturation (i.e., greater permeability of language transfer during adulthood), I posit the existence of a prior applied to the constraint weights during input evaluation.

Coda /s/ weakening is among the most studied phonological phenomena in Spanish, and variationists have shown that /s/ weakening and complete deletion are conditioned by many factors. Though complete deletion of a plural /s/ may occasion homophony with singular items in Spanish, few studies have examined the acoustic and prosodic cues that speakers may use to signal plurality when a final /s/ is deleted. In this dissertation, I explore cues used by speakers and listeners of Chilean Spanish, an /s/ weakening variety, to distinguish plural from singular Noun Phrase (NP) constituents in both speech production and perception. I analyze acoustic cues of duration, vowel quality, and breathiness from the sociolinguistic interviews of 60 Santiago residents grouped by age and gender, comparing singular word-final vowels to plural word-final vowels with the final /s/ completely deleted. These 60 participants also took part in a two-alternative forced-choice perception task, asked to identify plurality on isolated natural stimuli extracted from sociolinguistic interviews. I determined that utterance-medial vowel shortening is a cue for plurality, produced and perceived by only members of the middle age groups across genders and SES groups demonstrating age grading and overall community stability. Additionally, breathiness is a prestigious cue for plurality produced and perceived reliably by high SES speaker-listeners, and produced by younger members of the lower SES as well, though these low SES speakers do not perceive breathier vowels as plural. I posit that these younger speakers are adopting the use of breathy plural vowels in a change from above, and that the mismatch between production and perception signals the instability of the nascent change. Utterance-final lengthening is produced but not perceived by young females in the low SES, while middle- and older age group females in this neighborhood perceive breathier vowels as plural but do not produce them as such. Again, I posit that this mismatch signals instability of this cue as it is begun as a change from below by these low SES female speakers. Finally, plural vowel lowering is produced only by young males in the high SES group, but is perceived by all males and young females in both SES groups. It is therefore a perceptually robust but seemingly unreliable cue, signaling some type of instability. Plural vowel raising, on the other hand, is produced by middle- and older age group speakers in the lower SES, but not perceived by any groups. I therefore posit that plural raising is moving toward loss, as younger speakers in the low SES do not produce their singular and plural vowels with any F1 differences.

In sum, this dissertation contributes findings from both production and perception, offering the first acoustic evidence for shifts in multiple directions of the several cues that mark the singular~plural distinction in this /s/ weakening dialect of Spanish.

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