Focused attention during selective adaptation along a place of articulation continuum

The current investigation manipulated subjects' attention to adaptor tokens in five selective adaptation experiments. All stimuli were synthetic consonant-vowel syllables, with the consonant varying from [b] to [d] by formant frequency transitions. Two distractor conditions (auditory and visual) were compared to a more typical endpoint-[d alpha] adaptor condition. Distraction from endpoint-[d alpha] adaptors to phonetically distinct [si] and [integral of i] was used to observe whether smaller adaptation effects would result when attention was not focused on adaptor stimuli. In contrast, a focused attention condition required subjects to whisper [b alpha] adaptors right after they were heard. Performance in the focused attention condition was compared to a more typical endpoint-[b alpha] adaptation condition. Results indicated that focused attention did not affect the size of the adaptation effect. Asymmetrical adaptation results for [d alpha] vs [b alpha] adaptors, and a larger amount of adaptation with the presence of contralateral "distractor" syllables, resembled findings in psychoacoustic studies of discrimination and loudness adaptation. These results suggest that two levels of auditory processing (not special to speech perception) were responsible for the observed adaptation effects.