LEARNING COMPLEMENTARY DISTRIBUTION

A number of studies have found evidence that suggests that pairs of sounds which belong to the same phoneme (sound pairs in a “phonemic” relationship) are processed differently than pairs of sounds which belong to the same phoneme (sound pairs in an “allophonic” relationship). In particular, listeners exhibit less sensitivity to sound pairs which are allophonic in their language compared to sounds which are pho- nemic (Peperkamp et al., 2003; Boomershine et al., 2008; Seidl and Cristia, 2012; Johnson and Babel, 2010). This could be attributed at least in part to the tendency for allophonic sound pairs to exhibit greater perceptual similarity than phonemic pairs (Pegg and Werker, 1997; Yuan and Liberman, 2011), but can- not be solely attributed to perceptual similarity. Boomershine et al. (2008) find that English speaking adults are less sensitive to the difference between pairs of phones which are allophonic in English ([ɾ] and [d]) than they are to pairs of phones which are phonemic in English ([d] and [ð]). However, Spanish speaking adults showed the opposite pattern: they showed low sensitivity to [d] and [ð], which are allo- phonic in Spanish, and greater sensitivity to [ɾ] and [ð], which are phonemic in Spanish. This suggests that lower sensitivity to allophonic pairs than to phonemic pairs cannot be solely attributed to a lesser per- ceptual distance between allophonic pairs, since the English and Spanish speakers showed the opposite pattern for the same phones [d] and [ð].

Seidl et al. (2009) finds evidence that the distinction between phonemic and allophonic relation- ships develops somewhere between 4 and 11 months of age. In an infant language learning study, Seidl and colleagues exposed English-learning and French-learning infants to a phonological pattern which de- pended on vowel nasality. Crucially, vowel nasality is contrastive in French, but not in English. The English-learning 4-month olds and French-learning 11-month olds were able to learn the pattern, but the

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English-learning 11-month olds were not, suggesting that sensitivity to a contrast which is not phonemic decreases by the time an infant is 11 months of age.

The studies above show that phonemic and allophonic pairs are processed and discriminated dif- ferently. However, there are only a few studies which have been designed to catch the acquisition process of an allophonic relationship and its associated change in sensitivity within the lab, the way that Maye and colleagues’ distributional learning experiments were able to measure a change in sensitivity caused by different frequency distributions within the lab. The remainder of this section summarizes findings from Peperkamp et al. (2003) and Noguchi (2016), who both test whether the predictability of a phone based on its phonetic environment can bring about a change in participant sensitivity.

Peperkamp et al. (2003) tested three groups of native French speakers: a Monomodal group, a Bi- modal group, and a Bimodal+Assimilation group. Critical stimuli consisted of tokens taken from an 8- point continuum ranging between the fricatives [ʁ] and [χ], each preceded by a vowel. These were fol- lowed by CV context syllables, which began with either a voiced or voiceless consonant, creating VCTarget + CVContext “phrases.” The Monomodal group heard a monomodal distribution of the fricatives [ʁ] and [χ] during the training phase, and both Bimodal groups heard them in a bimodal distribution. The Bi-

modal+Assimilation group only heard the [ʁ]-half of the continuum before voiced consonants, and the [χ]-half of the continuum before voiceless consonants. During the test phase, participants were presented with pairs of 2-word VC.CV “phrases,” and were asked whether the first words in these two phrases were the same or different. This test phase occurred once before the exposure phase, and once after. Peperkamp and colleagues found that the Bimodal group was the only group to show a significant difference between the pre- and post-test phases, but they found no significant interaction across groups. Peperkamp and col- leagues suggest that, since the Bimodal group resulted more learning (numerically) between pre- and post-test phases than the Bimodal+Assimilation group, environmental context may play a role in distribu- tional learning. However, given the lack of significant interaction across groups, the authors also caution that the results from their experiment are unclear. They also note that their experiment failed to replicate

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Maye and Gerken (2000), since there was no significant interaction between the Bimodal and Monomodal groups. Results may have been affected by the fact that Peperkamp and colleagues tested native speakers of French, who already have the phonological rule specified in the Bimodal+Assimilation group.

In a recent dissertation, Noguchi (2016) tested three groups of participants: a Non-Complemen- tary group, a Complementary group, and a Control group. The first two groups heard a bimodal distribution of critical syllables with the onset ranging from an alveopalatal fricative [ɕa] to a retroflex fricative [ʂa] in an 8-point continuum. (The Control group did not hear any of the critical syllables con- taining fricatives.) The Non-Complementary group heard all 8 points of the continuum following one of four context syllables, all of which ended with [i], and also all 8 points of the continuum following one of four context syllables, all of which ended with [u] (e.g. [liɕa], [liʂa], [luɕa], and [luʂa]) (see Figure 34, left).

Figure 34. Training distributions for Non-Complementary (left) and Complementary (right) conditions in Noguchi (2016).

The Complementary group only heard the four tokens on the [ɕa]-side of the 8-point continuum (referred to here as S1a-S4a) following syllables ending with [i], and the four tokens on the [ʂa]-side of the 8-point continuum (referred to here as S5a-S8a) following syllables ending with [u] (e.g. [liɕa] and [luʂa]) (see Figure 34, right). Subsequently, participants were tested on whether they believed the syllables presented in isolation were the “same” or “different” from one another. Noguchi found that the Complementary

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group had lower sensitivity (lower d’) than the Control and the Non-Complementary groups. Noguchi in- terprets this result as showing that the Complementary group treated [ɕ] and [ʂ] as allophones of the same phoneme.