Increased experience with an unfamiliar language decreases fixations to the mouth during encoding

Previous research has shown infants viewing speaking faces shift their visual fixation
from speaker’s eyes to speaker’s mouth between 4-8 mo. Lewkowicz & Tift, 2011. It is theorized
this shift occurs to facilitate language learning, based on audiovisual redundancy in speech. We
previously found adults gazed significantly longer at speaker’s mouths while seeing and hearing
non-native language compared with their native language. This suggested there may be
mechanisms in which gaze fixations to speaking mouths are increased in response to uncertainty
in speech. If so, increasing familiarity with speech signals may reduce this tendency to fixate the
mouth. To test this, the current study investigated the effect of familiarization to non-native
language on the gaze patterns of adults. We presented English-speakers with videos of sentences
spoken in Icelandic. To ensure encoding of the speech, participants performed a task in which
they were presented with videos of two different sentences, followed by an audio-only recording
of one of the sentences, and had to identify whether the first or second video corresponded to the
presented audio. In order to familiarize participants with the utterances, the same set of sentences
were repeated. These ‘repetition’ blocks were followed by additional ‘novel’ blocks, using
sentences not previously presented. We found the proportion of fixations directed at the mouth
decreased across repetition blocks, but were restored to their initial rate in the novel blocks.
These results suggest that familiarity with utterances, even in a non-native language, serve to
reduce auditory uncertainty, leading to reduced mouth fixations.