!Xóõ click perception by English, Isizulu, and Sesotho listeners 738

Catherine T. Best 1,2 Anthony Traill 3 Allyson Carter 4 K. David Harrison 2,5 Alice Faber 2 1 Wesleyan University 2 Haskins Laboratories 3 University of the Witwatersrand 4 University of Arizona 5 Swarthmore College (USA) Supported by NIH grants DC00403 & HD01994

Adult listeners find many but not all nonnative phonological contrasts difficult to discriminate. The Perceptual Assimilation Model (PAM, Best 1995) attributes those discrimination differences to the way listeners assimilate the nonnative phones to their native phonologies, which vary among languages. We tested perception of two !Xóõ click contrasts by speakers of American English vs. speakers of Isizulu and of Sesotho, two African click languages that lack the target contrasts. Both African groups were expected to assimilate the stimuli to native clicks and to discriminate them accordingly. Americans were expected to perceive them more often as non- ABSTRACT

speech and to discriminate both contrasts well. Because Isizulu has a richer click system than Sesotho, Isizulu listeners should assimilate !Xóõ clicks to native clicks more often, and discriminate at least one contrast better than Sesotho listeners. Americans should excel on any contrast that an African group assimilates to a single click. As predicted, Isizulu listeners most often assimilated !Xóõ clicks to native ones; Americans were most likely to hear them as nonspeech. Sesothos found one contrast more difficult to categorize and discriminate than the other groups. Both African groups assimilated the other contrast to a single native click, with lower discrimination than Americans.

BACKGROUND  Categorization and discrimination of unfamiliar nonnative phonetic contrasts is often difficult for adults but more recent research indicates that for some nonnative contrasts, perception may be good or excellent  What possible factor(s) may account for variations in perception of various nonnative contrasts by naïve adults?

Theoretical Models:  Speech Learning Model (SLM): Flege L2 learners hear individual nonnative phones as identical or similar to native phonemes, or as new  Natural Language Magnet model (NLM): Kuhl prototypes formed by native speech experience act as perceptual magnets to same-category neighbors  Fragile-Robust Hypothesis (FRH): Burnham psychoacoustically robust nonnative contrasts are more easily maintained and learned than fragile ones  Perceptual Assimilation Model (PAM): Best nonnative phones assimilated to articulatorily-similar native contrasts/phonemes or heard as nonspeech

Approach: Cross-linguistic perception tests  Research design: Listeners of languages that display crucial differences in phonological/phonetic details Mutually-nonnative stimulus contrasts that relate to listener languages in critically different ways  Theoretical considerations: SLM: equivalence classifications should vary across nonnative stimuli and listener groups NLM: stimulus properties should vary re: groups’ acoustic exposure and similarity to native prototypes FRH: stimulus contrasts should vary along the fragile-robust psychoacoustic dimension PAM: contrasts should differ among listener groups in expected assimilations to native contrasts

Choice of Stimuli & Listener Groups (Table 1)  !Xóõ click POA (place of articulation) contrasts (2): mutually nonnative: across groups that vary in potentially relevant acoustic/phonetic experience acoustic/phonetic similarity varies: re: contrasts and listener groups psychoacoustics vary: robust vs. more fragile contrast assimilations should vary: groups should differ in varied speech and nonspeech percepts of the clicks  Listener groups(3): American English: no click phonemes, tend to hear clicks as nonspeech sounds South African languages (2): both have clicks but lack the target POA contrasts and phonetic accompaniment  Isizulu has click POA contrasts, Sesotho does not

Table 1

Predictions:  Speech Learning Model (SLM): Isizulu : [áx] is new while [ ñx] is similar to native [ñ]), thus [áx]- [ ñx] is easy to discriminate. [úx]- [ óx] are both similar to native [ó], thus difficult. Sesotho : [áx]- [ ñx] are both new, thus easy. [úx]- [ óx] are both similar to native [ó], thus difficult. Americans : All clicks new, thus both contrasts easy.  Fragile-Robust Hypothesis (FRH): [úx]- [ óx] contrast is psychoacoustically extremely salient, [áx]- [ ñx] is notably less salient; the more robust contrast should be easier to discriminate. Both contrasts are nonnative to all groups, thus no group differences are expected.

 Natural Language Magnet model (NLM): Isizulu : [áx] and [úx] non-protoypes, [ ñx] and [ óx] attracted to native [ñ]) and [ó] prototypes, thus both contrasts moderately, equally easy to discriminate. Sesotho : [ óx] attracted to native [ó], all others are non-prototypes, thus [áx]- [ ñx] easier than [úx]- [ óx]. Americans : All clicks are non-protoypes, thus both contrasts very easy to discriminate.  Perceptual Assimilation Model (PAM): Isizulu : [ ñx] assimilated to native [ñ]) better than [áx], both [úx]- [ óx] assimilated to native [ó], thus [áx]- [ ñx] (Category Goodness) > [úx]- [ óx] (Single Category). Sesotho : all clicks assimilate to native [ó], thus both contrasts difficult; worse than Isizulus on [áx]- [ ñx]. Americans : more likely to hear clicks as nonspeech; should discriminate [úx]- [ óx] better than other groups.

METHODS  Participants: American English (n = 16) from northeast United States Isizulu (n = 13) from Kwazulu-Natal Province, South Africa Sesotho (n = 13) from the Southern Sotho area of Free State Province, South Africa additional inclusion requirements:  native speakers of respective languages  no experience with !Xóõ or similar click systems  tested in native language and country

 Stimuli (Figures 1 & 2, Table 2): !Xóõ speaker: adult female from Lokalane, Botswana stimulus tokens: 4 /Ca/ syllables with velar- fricated clicks, 5 tokens each: áx, ñx, úx, óx POA contrasts: both nonnative to all Ss  bilabial - dental [áx] [ ñx] (more fragile)  palatal - alveolar [úx] [óx] (robust)  Tasks: (separately for each contrast): Discrimination: categorial AXB Categorization: labeling (re: native phonemes and/or nonspeech sounds) and goodness ratings of all individual tokens

Bilabial [ áx ] Dental [ ñx ] Example tokens: bilabial/dental click contrast Figure 1

Palatal [ úx ] Alveolar [ óx ] Example tokens: palatal/alveolar click contrast Figure 2

Table 2

RESULTS  Categorization (Figures 3 & 4, Table 3): Americans perceived nonspeech (fully or partially) most often, especially for dental and alveolar clicks. Sesotho listeners perceived more nonspeech than Isizulu listeners, except for palatal clicks. Sesothos assimilated both contrasts equally to native [ ó ], as did Isizulus for [úx]- [ óx], but they heard a goodness difference in [áx]- [ ñx].  Discrimination (Figure 5): Sesothos were equally poor on both contrasts. Isizulus did better on [áx]- [ ñx] than [úx]- [ óx]. Americans did better on [úx]- [ óx] than [áx]- [ ñx] and better on [úx]- [ óx] than both Sesothos and Isizulus.

Figure 3

Figure 4

Table 3

Figure 5 [úx]- [ óx] [áx]- [ ñx]

CONCLUSIONS  Theoretical implications: SLM and NLM and FRH predictions all failed to account for one or more findings PAM predictions were most straightforwardly supported by the results.  Counter-intuitive result predicted by PAM: Americans, who lack linguistic experience with clicks, outperformed the click-experienced Isizulu and Sesotho listeners on one contrast  Further research: confirm and extend to other groups/contrasts assess the types of stimulus information non- native listeners use (e.g., acoustic, articulatory)

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Bilabial [ áx ] Dental [ ñx ] Palatal [ úx ] Alveolar [ óx ]