Information flow, artificial phonology and typology

In the context Artificial Grammar Learning (AGL) experiments, it is possible to quantify how effectively a stimulus has conveyed information and specifically the information the experimenter thinks it was designed to convey. At the most basic level, this can be done if one has access to the response variability of independent responses to the same stimulus (or subparts of the stimulus). The variability of these responses serves as an index of the amount of information that flows from the source of the stimulus to the perceiver. Quantifying information flow in this way, it is shown that under conditions where participants learn a ‘natural’ but not an ‘unnatural’ rule there are asymmetries in entropic quantities under the different conditions

The /el/-/æl/ merger in Australian English:Acoustic and articulatory insights

This paper investigates a merger-in-progress of /e/-/æ/ in prelateral contexts for speakers of Australian English in Victoria. Twelve participants (7F, 5M) were recorded producing a wordlist resulting in acoustic and concurrent articulatory data via stabilised mid-sagittal ultrasound tongue imaging. Focusing on a subset of the data comprising short front vowels /ɪ, e, æ/ in /hVt/ and /hVl/ contexts, findings show that there are robust acoustic differences between /e/ and /æ/ preceding /t/, as anticipated. However, individual differences emerge for /e/ and /æ/ preceding /l/, with highly gradient production patterns across the speakers, ranging from speakers who exhibit merger behaviour to those who maintain categorical distinctions. The evidence for merging behaviour across speakers is similar, but does not map directly, across both the acoustic and articulatory data, and illustrates the value of incorporating a range of data types in investigating a merger-in-progress

Consonant harmony, disharmony, memory and time scales

I argue that properties of memory offer an appropriate grounding for a number of characteristics of long distance consonantal co-occurrence restrictions whose basis had so far remained unclear

Associating the origin and spread of sound change using agent-based modelling applied to /s/-retraction in English

The study explored whether an asymmetric phonetic overlap between speech sounds could be turned into sound change through propagation around a community of speakers. The focus was on the change of /s/ to /ʃ/ which is known to be more likely than a change in the other direction both synchronically and diachronically. An agent-based model was used to test the prediction that communication between agents would advance /s/-retraction in /str/ clusters (e.g. string). There was one agent per speaker and the probabilistic mapping between words, phonological classes, and speech signals could be updated during communication depending on whether an agent listener absorbed an incoming speech signal from an agent talker into memory. Following interaction, sibilants in /str/ clusters were less likely to share a phonological class with prevocalic /s/ and were acoustically closer to /ʃ/. The findings lend support to the idea that sound change is the outcome of a fortuitous combination of the relative size and orientation of phonetic distributions, their association to phonological classes, and how these types of information vary between speakers that happen to interact with each other

Combining research methods for an experimental study of West Central Bavarian vowels in adults and children

The overall goal of this thesis was to systematically measure defining vowel characteristics of the West Central Bavarian (WCB) dialect for an acoustically based analysis of the Bavarian vowel system and simultaneously investigate to what extent these characteristics are being preserved across generations and if there is a sound change in progress observable in which young speakers show more characteristics of Standard German (SG) than old on some Bavarian vowel attributes. In order to address these aims we conducted acoustic recordings of WCB speaking adults and WCB speaking primary school children which were then compared to each other with an apparent-time analysis. For a more accurate view of changes in progress we combined this apparent-time comparison with longitudinal data from the WCB children, obtained at annually intervals expanding over three years. The acoustic data was enhanced by articulatory data gained from ultrasound recordings of a subset of the same WCB speaking children at two timepoints with one year interval. Analyses of the acoustic data revealed both adult/child and longitudinal changes in the direction of the standard in the children’s tendency towards a merger of two open vowels and a collapse of a long/short consonant contrast, neither of which exist in SG. There was some evidence that children in comparison with adults were beginning to develop both tensity and rounding contrasts which occur in SG but not WCB. There were no observed changes to the pattern of opening and closing diphthongs which differ markedly between the two varieties. Also, within the WCB front vowel that resulted historically from /l/-vocalization and for which articulatory data from a subset of the children was put into relation with the acoustic measures no changes were observed. The general conclusion is that WCB change is most likely to occur as a consequence of exaggerating phonetic variation that already happens to be in the direction of the standard and therefore internal factors motivated by general principles of vowel change might play a more decisive role in inducing a shift than external factors like dialect contact

Perceptual Asymmetry and Sound Change: An Articulatory, Acoustic/Perceptual, and Computational Analysis

Previous experimental study of the identification of stop and fricative consonants has shown that some consonant pairs are asymmetrically confused for one another, with listeners’ percepts tending to favor one member of the pair in a conditioning context. Researchers have also suggested that this phenomenon may play a conditioning role in sound change, although the mechanism by which perceptual asymmetry facilitates language change is somewhat unclear. This dissertation uses articulatory, acoustic, and perceptual data to provide insight on why perceptual asymmetry is observed among certain consonants and in specific contexts. It also uses computational modeling to generate initial predictions about the contexts in which perceptual asymmetry could contribute to stability or change in phonetic categories. Six experiments were conducted, each addressing asymmetry in the consonant pairs /k/-/t/ (before /i/), /k/-/p/ (before /i u/), /p/-/t/ (before /i/), and /θ/-/f/ (possibly unconditioned). In the articulatory experiment, vocal tract spatial parameters were extracted from real-time MRI video of speakers producing VCV disyllables in order to address the role of vocal tract shape in the target consonants’ vowel-dependent spectral similarity. The results suggest that, for consonant pairs involving /k/, CV coarticulation creates—as expected—vocal tract shapes that are most similar to one another in the environment conditioning perceptual asymmetry. However, CV coarticulation was less informative for explaining the vocalic conditioning of the /p/-/t/ asymmetry. In the second experiment, RF models were trained on acoustic samples of the target consonants from a speech corpus. Their output, which was used to identify frequency components important to the discrimination of consonant pairs, aligned well with these consonants’ spectral characteristics as predicted by acoustic models. A follow-up perception experiment that examined the categorization strategies of participants listening to band-filtered CV syllables generally showed listener sensitivity to these same components, although listeners were also sensitive to band-filtering outside the predicted frequency bands. Perceptual asymmetry is observed in CV and isolated C contexts. In the fourth experiment, a Bayesian analysis was performed to help explain why perceptual asymmetry appears when listening to isolated Cs, and a follow-up perception experiment helped to evaluate the relevance of this analysis to human perception. For /k/-/t/, for example, whose confusions favor /t/, this analysis suggested that [t] and [k] both have the highest likelihood of being generated by /t/ (relative to likelihood of /k/ generating each) in the context conditioning asymmetry. The follow-up study suggests listeners are more likely to categorize a [t] and [k] as /t/ if it has higher likelihood of being generated by /t/ (relative to /k/). The final experiment used agent-based modeling to simulate the intergenerational transmission of phonetic categories. Its results suggest that perceptual asymmetry can affect the acquisition of categories under certain conditions. A lack of reliable access to non-phonetic information about the speaker’s intended category or a tendency not to store tokens with low discriminability can both contribute to the instability of phonetic categories over time, but primarily in the contexts conditioning asymmetry. This dissertation makes several contributions to research on perceptual asymmetry. The articulatory experiment suggests that confusability can be mirrored by gestural ambiguity. The Bayesian analysis could also be used to build and test predictions about the confusability of other sounds by context. Finally, the model simulations offer predictions of the conditions where perceptual asymmetry could condition sound change.PHDLinguisticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155085/1/iccallow_1.pd