Perturbed speech How compensation mechanisms can inform us about phonemic targets

The present study describes the results of a 2 week perturbation experiment where speakers’ vocal tract shape was modified due to the presence of an artificial palate. The aim of the work is to investigate whether speakers adapt towards acoustic or articulatory targets. Speakers were recorded regularly over the adaptation time via electromagnetic articulography and acoustics. Immediately after perturbation onset speakers’ auditory feedback was masked with white noise in order to investigate speakers’ compensatory behaviour when auditory feedback was absent. The results of acoustic measurements show that in vowel production speakers compensate very soon. The compensation in fricatives takes longer and is in some cases not completed within the two weeks. Within a session and for each speaker the sounds can be distinguished solely by acoustic parameters. The difference between the session when no auditory feedback was available and the session when auditory feedback was available was greater for vowels with less palatal contact than for vowels with much palatal contact. In consonant production auditory feedback is primarily used in order to adapt sibilant productions. In general, adaptation tries to keep or enlarge the articulatory and acoustic space between the sounds. Over sessions speakers show motor equivalent strategies (lip protrusion vs. tongue back raising) in the production of /u/. Measurements of tangential jerk suggest that after perturbation onset there is an increase in articulatory effort which is followed by a decrease towards the end of the adaptation time. The compensatory abilities of speakers when no auditory feedback is available suggest that speakers dispose of an articulatory representation. The fact that motor equivalent strategies are used by the speakers, however, supports acoustic representations of speech. It is therefore concluded that articulatory representations belong to the speech production tasks. However, since they are modified as soon as the acoustic output is not the desired one any more, they rather function in the domain of movement organisation and the acoustic representations dominate.