Аннотация
When a single flash of light is presented interposed between two brief
auditory stimuli separated by 60–100 ms, subjects typically report
perceiving two flashes (Shams et al., 2000, 2002). We investigated
the timing and localization of the cortical processes that underlie
this illusory flash effect in 34 subjects by means of 64-channel
recordings of event-related potentials (ERPs). A difference ERP calculated
to isolate neural activity associated with the illusory second flash
revealed an early modulation of visual cortex activity at 30–60 ms
after the second sound, which was larger in amplitude in subjects
who saw the illusory flash more frequently. These subjects also showed
this early modulation in response to other combinations of auditory
and visual stimuli, thus pointing to consistent individual differences
in the neural connectivity that underlies cross-modal integration.
The overall pattern of cortical activity associated with the cross-modally
induced illusory flash, however, differed markedly from that evoked
by a real second flash. A trial-by-trial analysis showed that short-latency
ERP activity localized to auditory cortex and polymodal cortex of
the temporal lobe, concurrent with gamma bursts in visual cortex,
were associated with perception of the double-flash illusion. These
results provide evidence that perception of the illusory second flash
is based on a very rapid dynamic interplay between auditory and visual
cortical areas that is triggered by the second sound.
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