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Abstract:
Hemispheric Encoding/Retrieval Asymmetry (HERA) is a model of
episodic memory born out of neuroimaging data that suggests that
episodic encoding is predominantly a left hemisphere function and
that episodic retrieval is predominantly a right hemisphere
function (Tulving et al., 1994). If this model is true, then a
disconnection of the two hemispheres should produce significant
effects on episodic memory. Yet, most callosotomy patients show
only a slight impairment on free recall tests and no impairment on
recognition tests. We specifically tested for encoding asymmetries
using the same levels-of-processing manipulation as neuroimaging
studies showing activation in the left prefrontal cortex for
semantic retrieval and episodic encoding. We hypothesized that the
left hemisphere should benefit more from elaborative encoding tasks
than the right. Two patients were tested (J.W. and V.P.).
Experiment 1 used simple word lists and compared shallow encoding
(does the word contain the letter "a") with deep encoding
(living/nonliving). Experiment 2 used faces and again compared
shallow encoding (male/female) with deep encoding (healthy/not
healthy). Experiment 1 confirmed the model showing that the left
hemisphere significantly benefited from the elaboration but the
right did not, while Experiment 2 disconfirmed the model by showing
that the right hemisphere benefited from the elaboration but the
left did not. These data suggest that asymmetries in episodic
memory tasks reflect processing asymmetries and not encoding
asymmetries. Research supported by a grant from NIH
RO1-NS31443.
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