What this means for learners
PAYA and Chasta Costa share 16 sounds — roughly 36% of Chasta Costa's inventory overlaps with PAYA. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 28 sounds found only in Chasta Costa represent the greatest pronunciation challenge for PAYA speakers. The adult brain tends to map unfamiliar sounds onto the closest native equivalent — a process that produces the characteristic "accent" of a second-language speaker. Learning to hear and produce these sounds as distinct requires focused ear training, not just repetition.
Conversely, PAYA has 12 sounds not used in Chasta Costa. Native Chasta Costa speakers learning PAYA will face the mirror-image challenge with these sounds.
Phoneme inventories from PHOIBLE. Data reflects one documented inventory per language; some variation exists across dialects and sources.