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Abstract:
For social interaction and survival primates rely
heavily on vocal and facial communication signals
from their conspecifics. To date many studies have
evaluated the unisensory representations of either
vocal or facial information in regions thought to be
voice or face selective. Other studies have directly
evaluated the multisensory interactions of voices
and faces but have focused on posterior auditory
regions closer to the primary auditory cortex. This
work investigates multisensory interactions at the
neuronal level in an auditory region in the anterior
superior temporal plane, which contains one of
the regions important for processing voice-related
information.
Extracellular recordings were obtained from the
auditory cortex of macaque monkeys, targeting
an anterior voice region that we have previously
described with functional magnetic resonance
imaging (fMRI, Fig. 1A). For stimulation we used
movies of vocalizing monkeys and humans which
we matched in their low-level auditory and visual
features. These dynamic face and voice stimuli
allowed us to evaluate how neurons responded
to auditory, visual or audio-visual components of
the stimuli. Our experiments also contained control
conditions consisting of several mismatched audiovisual
stimuli combinations, such as 1) a voice
matched to a face from a different species, 2) adding
a temporal delay in the visual component of the
stimulus, or 3) using an acoustically manipulated
voice with the original facial stimulus.
Our neuronal recordings identified a clustered
population of voice-selective sites in the anterior superior temporal plane, ~5 mm anterior to the
tonotopically organized field RT (Fig. 1B). A significant
visual influence of the dynamic faces on
the corresponding (matched) vocalizations was observed
in both the local-field potential (LFP) and the
spiking activity (analog multiunit activity, AMUA):
38 of the sites showed audiovisual interactions
in the LFP signals, and 60 in the AMUA (Fig.
2). In addition, the multisensory influence was significantly
stronger for the matching voice and face
stimuli than to any of the incongruent (mismatched)
control conditions, confirming the specificity of the
cross-sensory influence on the neuronal activity.
Our results provide evidence for visual influences
in what has been characterized as an auditory
‘voice’ area. This visual modulation was specific for
behaviorally relevant voice-face associations and
demonstrates that the processing of voice-related
information in higher auditory regions is influenced
by multisensory input.
