| dc.description.abstract | Research has shown considerable change in audio-visual speech perception across the
lifespan, in particular during childhood and old adulthood. However, changes between young
and middle adulthood have received relatively little attention. The intention of the current
project was to contribute to a more comprehensive lifespan understanding of audio-visual
speech perception by investigating changes in this age interval. The three studies included
explored age differences in audio-visual speech perception from two different perspectives:
audio-visual identification and audio-visual asynchrony perception. Audio-visual speech
identification relates to the ability to use the multitude of auditory and visual speech
information to recognize and label speech segments, such as stop consonants in the case of
this study. Audio-visual asynchrony perception in contrast, is a more basic ability, reflecting
the temporal thresholds for whether the auditory and the visual speech signals are integrated
into a single audio-visual percept. All the experiments included have one thing in common:
the assessment of age-related experience through comparison of young and middle-aged
participants. All studies also used speech stimuli of the same complexity, namely syllables
composed of different stop consonants trailed by a vowel.
The first experiment explored age differences in audio-visual asynchrony perception.
Participants made simultaneity judgements, that is, decided whether the auditory and visual
signals were synchronous or asynchronous for audio-visual stimuli ranging from 440
millisecond audio-lead to 440 millisecond visual-lead. Whereas visual-lead sensitivity was
unaffected by age, middle-aged adults were significantly more sensitive to audio-lead
asynchronies than young adults. It was suggested that in contrast to visual-lead asynchrony,
the natural temporal predictability of audio-lead asynchronies makes audio-lead sensitivity
more susceptible to the predictability dependent perceptual learning. Hence, that age affected
audio-lead asynchrony perception specifically suggests a contribution of audio-visual speech
experience, especially since age-related sensory and cognitive differences were assessed to be
minor.
The second experiment was a continuation of the first, and in addition to using a
similar simultaneity judgement task, employed a measurement of cognitive processing speed.
Cognitive processing speed was assessed through recognition reaction time tasks where
participants responded as quickly as possible to the syllable /ba/ amid presentations of /da/ and /ga/ syllables. The first aim of the experiment was to evaluate the relationship between
cognitive processing speed and audio-visual asynchrony perception. The second aim was to
assess the effect of age on this relationship. The results confirmed the notion put forward in
the first experiment, that young and middle-aged adults have similar cognitive processing
speed. The result of the young adults also confirmed the proposed relationship between
cognitive processing speed and audio-visual asynchrony perception, that is, increasing
reaction time was associated with increasing tolerance for audio-visual asynchrony. However,
the lack of such a correlation for the middle-aged adults implied that age-related audio-visual
experience mitigates the influence of cognitive processing speed on audio-visual asynchrony
perception. It was suggested that middle-aged adults’ audio-visual experience may facilitate
selective attention, thus reducing the influence cognitive processing strain by focusing on the
most relevant audio-visual speech cues.
The third experiment investigated age and gender differences in audio-visual speech
identification. Audio-visual benefit and visual influence were used to measure the visual
contribution to audio-visual speech identification. Audio-visual benefit measured proficiency
in auditory-visual integration, and revealed no age and gender differences in performance.
Visual influence on the other hand quantified the individual contribution of auditory and
visual speech cues in audio-visual speech identification, and whereas no gender difference
was observed for the young adults, the middle-aged females relied significantly more on
visual cues in audio-visual speech identification than middle-aged males. It was proposed that
the gender difference in visually influenced responses in middle adulthood is a result of an
experience-related shift in the audio-visual perceptual strategy of females. Because females
were observed to be better speech-readers in both age groups, it was suggested that speechreading
proficiency in young adulthood could gradually shift females’ audio-visual perceptual
strategy towards more visual reliance in middle-adulthood.
Collectively, the three studies show that audio-visual speech perception is susceptible
to change between young and middle-adulthood. Together with previous research on
childhood and older adulthood, these findings underpin the flexibility and ever-evolving
nature of audio-visual speech perception across the lifespan. That cognitive processing speed
and gender interact with age-related audio-visual experience exemplifies the value of a
lifespan perspective when exploring other influences on audio-visual speech perception. | nb_NO |
