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Abstract:
This study examined ERP effects in an anomalous story
paradigm in which stimuli were composed entirely of complex
pictures designed to discourage verbal naming. EEG was recorded
from 29 scalp sites on 16 subjects. Each of 80 trials was composed
of a series of gray-tone pictures (1500 ms duration and 300 ms ISI)
which told a simple story. The final frame of each story was either
congruous or incongruous with the preceding context. Trials were
presented randomly and were counterbalanced across subjects. After
the final frame of each story subjects made a delayed
meaningfulness judgment. Averaged ERPs time-locked to the onset of
the final frames revealed two components sensitive to congruency.
The first component had a peak effect at 360 ms and was distributed
over central and frontal sites with little hemispheric asymmetry.
The second component peaked at 510 ms and also had a centro-frontal
distribution but was larger over the right hemisphere. These
results support previous findings of an early anterior negative
component that is specific to the semantic processing of pictures.
The distribution of the N510 for pictures is also suggestive of a
set of neural generators that is at least partially distinct from
that underlying the centro-parietally distributed N400 for words.
However, discrepancies in the strategies used by subjects to
perform this task suggest that some of these effects may be due to
verbal translation.
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