When do American-English infants learn that /d/ and /t/ alternate with a tap?

In English, some sounds change depending on the context. The verb ‘pat’ ends in a “hard” [t], but when used in the word ‘patting’, the [t] becomes a ‘ tap’. We’ve tested 8 and 12mo olds on their ability to associate ‘pat’ to ‘patting’, as well as ‘pad’ (ending in a softer consonant) to ‘padding’. While they succeed with ‘pad’, 8mos fail with ‘pat’. However, by 12mo, they succeed with both. We suspect that the more different the features of the consonant are, the longer it takes for them to create that consonantal alternation. We are currently developing stimuli to test other possible alternating phonemes that are not present in English (e.g., take – taging) to investigate whether infants have learned those alternations based on their input or based on their phonetic similarity.