When hearing speech, listeners begin recognizing words before reaching the end of the word. Therefore, early sounds impact spoken word recognition before sounds later in the word. In languages like English, most morphophonological alternations affect the ends of words, but in some languages, morphophonology can alter the early sounds of a word. Scottish Gaelic, an endangered language, has a pattern of 'initial consonant mutation' that changes initial consonants: Pog 'kiss' begins with [ph], but phog 'kissed' begins with [f]. This raises questions both of how listeners process words that might begin with a mutated consonant during spoken word recognition, and how listeners relate the mutated and unmutated forms to each other in the lexicon. We present three experiments to investigate these questions. A priming experiment shows that native speakers link the mutated and unmutated forms in the lexicon. A gating experiment shows that Gaelic listeners usually do not consider mutated forms as candidates during lexical recognition until there is enough evidence to force that interpretation. However, a phonetic identification experiment confirms that listeners can identify the mutated sounds correctly. Together, these experiments contribute to our understanding of how speakers represent and process a language with morphophonological alternations at word onset.

The primary claim of this dissertation is that children and adults process language in the same manner, meaning that when children are acquiring their first language what they are truly doing is perfecting their language processing abilities. Language acquisition and processing both start from the same place. Both work to find patterns in the signal that will, eventually, be paired with meaning. This dissertation argues that differences in how children and adults accomplish these tasks are one of degree and not kind. To show this, three experiments tested how adults and children responded to a conflict between the lexical and prosodic parse of an utterance. The participants’ response to this conflict reveals information about where they are in the language acquisition process. In these experiments, prosody was used to disambiguate phrases that can be interpreted either as a list of two items (e.g., fruit, salad) or as a single compound item (e.g., fruit-salad). Prosody was also made to conflict with the lexical parse of an utterance. When the word cactus is said with List Prosody two non-words /kæk/ and /tʌs/ result. When the words nail and key are said with Compound Prosody, the non-word nailkey is created. By exploiting the overlap between the prosodic system and the lexical system, it is possible to evaluate how language is being processed. The results show that adults tend to parse utterances based on the lexical content, and ignore ambiguities created by a conflict between the prosodic and the lexical interpretation of the phrase. In contrast, children tend to respond based on the prosody, making increasing use of the lexical content as they mature. When the same items are tested with abstract shapes rather than representational images, adults make greater use of prosody. This suggests that visual input plays a role in spoken word processing. The dissertation also proposes a modified model of spoken word recognition that accounts for the difference seen between the adults and the children, and for the effect of visual content. This model integrates phonetic details, prosodic content, lexical knowledge, visual content, and pragmatic understanding during spoken word recognition.

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All current theories of spoken word recognition (e.g., Allopenna et al., 1998; McClelland & Elman, 1986; Norris, 1994) suggest that any part of a target word triggers activation of candidate words. Visual world paradigm studies have relied on the linking hypothesis that the probability of looking at the referent of a word directly tracks the word’s level of activation (e.g., Allopenna et al., 1998). However, how much information is needed to trigger a saccade to a visual representation of the word’s referent? To address this question, the present study manipulated the number and location of shared segments between the target and competitor words. Experimental evidence is provided by two visual world paradigm experiments on Japanese, using natural and synthesized speech. In both experiments, cohort competitor pictures were not fixated more than unrelated distractor pictures unless the cohort competitor shares the initial CVC with the target. Bayesian analyses provide strong support for the null hypothesis that shorter overlap does not affect eye movements. The results suggest that a listener needs to accumulate enough evidence for a word before a saccade is generated. The human data were validated by an interactive computational model (TRACE: McClelland & Elman, 1986). The model was adapted to Japanese language to examine whether the TRACE model predicts competitor effects that fit human data. The model predicted that there should be effects when words share any amount with a target which confirms the current theory. However, the model did not fit the human data unless there is longer overlap between words. This indicates that eye movements are not as closely tied to fixation probabilities of lexical representations as previously believed. The present study suggests that looking at a referent of a word is a decision, made when the word’s activation exceeds a context-specific threshold. Subthreshold activations do not drive saccades. The present study conclude that decision-making processes need to be incorporated in models linking word activation to eye movements.

Research has shown that fine-grained consonantal phonetic information can be gradiently integrated during spoken word recognition in the L1. However, the way listeners categorize vocalic phonetic information has not been investigated as thoroughly. Furthermore, second language (L2) listeners’ processing of fine-grained information is not as well known as L1 processing. L1 Canadian French (CF) listeners and L2 listeners (native English) were tested in an eye tracking paradigm with words containing partially nasalized (CVN) and fully nasal (CṼ) vowels. Stimuli were designed to have variable nasalization duration on the vowel, and sometimes include a short nasal consonant word-finally. The main goals were to determine how nasalization duration influences word recognition in an L1 and an L2, and if variations in phonetic details are gradiently or categorically integrated. Results show that L1 listeners gradiently were able to identify the stimuli when they contained mismatching phonetic cues, while L2 listeners display more categorical patterns of recognition. When stimuli do not have conflicting phonetic cues, L1 listeners mostly identify words as CṼ, except when the vowel is not nasalized. For L2 listeners, the pattern was similar, but the rate of stimuli identification as phonological nasal (CṼ) was lower due to L1 transfer. These results support the hypothesis that L1 listeners have phonological representations that include fine-grained phonetic information and that they consider it when recognizing words. On the other hand, L2 listeners who have less experience in the L2 display more categorical recognition patterns, probably because their representations include coarser phonetic information or because they cannot access fine-grained representations, given the cognitive demands of L2 processing. When words do not contain conflicting phonetic cues, patterns of recognition of both L1 and L2 listeners seem more categorical, even though L2 listeners displayed lower rates of identification than L1 listeners overall. This uncertainty can also be due to less detailed phonological representations or to their inability to access all the necessary information to recognize words. Overall, these results suggest that fine-grained phonetic information gradiently impacts word recognition, that it is part of phono-lexical representations, and that L2 processing is qualitatively and quantitatively different from L1 processing.

Three eye-tracking experiments were conducted to explore the effects of phonological, semantic and root activation in spoken word recognition (SWR) in Saudi Arabian Arabic. Arabic roots involve both phonological and semantic information, therefore, a series of three studies were conducted to isolate the effect of the root independently from phonological and semantic effects. Each experiment consisted of a series of trials. On each trial, participants were presented with a display with four images: a target, a competitor, and two unrelated images. Participants were asked to click on the target image. Participants' proportional fixations to the four areas of interest and their reaction times (RT) were automatically recorded and analyzed. The assumption is that eye movements to the different types of images and RTs reflect degrees of lexical activation. Experiment 1 served as a foundation study to explore the nature of phonological, semantic and root activation. Experiment 2A and 2B aimed to explore the effect of the Arabic root as a function of semantic transparency and phonological onset similarity. Growth Curve Analyses (Mirman, 2014, GCA;) were used to analyze differences in target and competitor fixations across conditions. Results of these experiments highlight the importance of phonological, semantic and root effects in SWR in Arabic. Fixations to competitors were graded and corresponded to the different amounts of phonological, semantic and morphological overlap between targets and competitors. The results of this work highlight the importance of the Arabic consonantal root as an independent processing unit in lexical access in SWR in Arabic that is separable from phonological and semantic units of processing. Finally, the results of this work provided support to models of SWR that feature both whole-word processing as well as morphological decomposition (e.g. Baayen, Dijkstra, & Schreuder, 1997; Giraudo & Grainger, 2000; Schreuder & Baayen, 1997). They also provide support to the morpheme-based theory of Arabic morphology (McCarthy, 1979, 1981).

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