Norris et al. (2002)
Introduction
-Infants ~6 months of age can still discriminate phonetic contrasts in non-native languages; lose this skill by 10 months of age in favor of better discrimination of native language phonetic contrasts; this is important for minimal pair discrimination; phonetic categorical modulation seems to occur based on lexical information, perhaps accounting for regional dialect/pronunciation changes
-Does lexical information feed back to pre-lexical selection of phonemes? This study tests this theory. Feedback systems for learning distinct from "on-line" feedback systems.
Experiment 1
-Speakers presented with recordings of fluent Dutch speaker for training, 3 groups of subjects. Group 1 heard 20 words ending with ambiguous /f/-/s/ spectrum sounds followed by 20 words with unambiguous /s/ sounds. Group 2 heard 20 words ending with ambiguous /f/-/s/ spectrum sounds followed by 20 words with unambiguous /f/ sounds. 3rd group was control, heard ambiguous /f/-/s/ continuum endings for all words. Groups were given a lexical decision and phoneme categorization task on 3 lists of words similar to the training words, with some filler. Results: Subjects were faster to label unambiguous-ending words as legal words than words with ambiguities, unsurprisingly. Subjects who heard ambiguous /f/ sounds and unambiguous /s/ sounds were more likely to categorize an ambiguous sound as /f/, and the opposite was true of the second group. This supports the hypothesis of feedback from lexical context cues. However, the authors note that this result could have been the result of selective adaptation to a fricative along the /f/-/s/ continuum, or due to "a contrast between the ambiguous phoneme and the unambiguous endpoint." (p.15)
Experiment 2
Kraljic et al. (2006)
Introduction
-Listeners attempt to make auditory perception more consistent through a process called normalizing, which makes up for fluctuations in the acoustic signal. They do this by maintaining a few, broadly defined phonemic categories in order to account for variations in speech. Recently, research has shown that people may adjust to speakers by narrowing these phonetic categories based on context and speaker variation, which the text refers to as perceptual learning or perceptual recalibration. The article makes references to Norris et al. (2003) in which listeners adjusted their perceptual categories to adjust to the acoustic signal in an ambiguous context, but goes on to suggest that perceptual learning may happen on a speaker, word or even phonemic level. The following experiment is conducted to see the extent of perceptual learning that listeners have when presented with a speaker which produces an odd phoneme, in this case, /d/.
Experiment 1