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Abstract:
Abstract: The prefrontal cortex is involved in the planning
of action. It has been postulated that actions are represented in
memory as hierarchically organized sequences of goal-directed
discrete events (Schank and Abelson, Erlbaum, 1977). In previous
studies, we showed during script generation that patients with
prefrontal cortex damage are selectively impaired in action
sequence ordering (Sirigu et al., Cortex, 31,301-316,1995). Here we
investigate the ability to detect boundaries between events in a
sequence, in five patients with prefrontal lesions and in twelve
normal controls. Following a method proposed by Hanson and Hirst
(J. Exp Psychol., 118,136-147, 1989.), subjects were presented with
soundless videotaped scenarios showing actors performing actions,
and requested to mark the end of each event under three different
conditions (1) spontaneous segmentation; (2) small-event oriented
instructions (3) large-event oriented instructions. Both subjects
and patients identified significantly more boundaries under
small-event than large-event instructions. However, patients with
prefrontal damage were selectively impaired at detecting the
boundaries of large events. These results indicate that although
prefrontal patients are capable of detecting transitions between
brief and/or discrete action intervals, sequence segmentation and
chunking processes may be required at a higher-order level in order
to perceive action sequences as meaningful units.
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