This dissertation begins with the observation of a typological asymmetry within phonological patterns related to phonetic naturalness. Patterns that are rooted within existing tendencies of perception and/or production -- in other words, patterns that are phonetically "natural" -- are common in phonological typology and seen in a variety of unrelated languages. Phonetically "unnatural" patterns, which are not based in these perceptual and/or production tendencies or which actively work against them, are either typologically rare or unattested. This observation has been noted in numerous works in phonology, and the debate over the nature of this asymmetry has spanned the past few decades. This dissertation makes a contribution to this debate.
There are two major arguments as to what underlies this observed typological asymmetry. One argument suggests that the bias against unnatural patterns is due to constraints on pattern learning. Learners have an innate knowledge of phonetic factors, and this knowledge predisposes them towards learning natural patterns and away from learning unnatural patterns. I refer to this argument as the universal learning bias account. The other argument suggests that the bias against unnatural patterns is rooted in perception and production. Since unnatural patterns work against phonetic tendencies, they are more difficult to perceive and/or produce than their natural counterparts and are more likely to be filtered out of typology through the forces of sound change. Under the channel bias account, the asymmetry can be explained by systematic errors in transmission that veer in the direction of natural patterns.
This dissertation explores predictions of the channel bias account using experimental methodology. A common practice within laboratory phonology is to test for naturalness-based asymmetries using artificial grammar experiments. Participants are assigned to learn one of two artificial patterns -- a natural pattern or its unnatural equivalent -- and then are tested on how well they learned their pattern. The results of these experiments, however, are often quite mixed: some experiments find that the natural pattern was learned more successfully, while others find no performance differences between the two patterns. This has led researchers to question how robust these naturalness effects truly are, and whether or not they can reliably be recreated in the lab.
I argue that the channel bias account holds a solution to this issue: namely, that proper presentation of experimental stimuli matters. Simply presenting stimuli to participants in slow, hyperarticulated speech is not enough. In order to reliably see an effect of naturalness, the phonetic differences between the patterns must be encoded into the design and presentation of the stimuli. This dissertation focuses on pattern pairs where the asymmetry is based in perception, hypothesizing that the natural pattern will be learned more successfully than the unnatural pattern if and only if the stimuli of the natural pattern are also perceived more successfully. In this way, the cross-experimental inconsistencies are easily predicted by the channel bias account, while the universal learning bias account fails to provide an explanation.
This dissertation uses experimental methods to argue for the channel bias account in three different phonological domains. In the domain of weight-sensitive stress, an artificial pattern that was both natural and formally simple was learned more successfully than two unattested patterns: one which was unnatural but formally simple, and one which was complex but natural. Perceptual difficulty could explain the poor performance within the unnatural pattern, but not within the complex pattern. Following this, I propose a 2x2 factorial template for testing for naturalness in the lab, wherein participants are assigned to learn one of two patterns (natural or unnatural) in one of two voice qualities (careful or casual). It is predicted that the group learning the unnatural pattern in casual speech will struggle to both perceive and learn their pattern; in careful speech, the unnatural pattern should be both perceived and learned with relative ease. Two experiments in the domains of final devoicing and coda sonority demonstrate evidence for the channel bias account using this experimental design.