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Abstract:
In the Psychological Refractory Period (PRP) paradigm two
unmasked targets are presented, each requiring a speeded response.
Response times to the second target (T2) are slowed when T1 is
presented within half a second of the first target (T1).
Previously, electrophysiology studies have shown that the P300
event related potential (ERP) component is not delayed, but the
lateralized readiness potential is delayed during T2 response
slowing in the PRP paradigm, presumably indicating a bottleneck on
response selection operations, not stimulus identification.
Recently researchers have also found T2 response slowing when T2
follows a masked T1 that requires encoding, but not speeded
responding. Behaviorally, the T2 response slowing from this task is
indistinguishable from that observed in the PRP paradigm, prompting
some researchers to postulate that response selection and stimulus
identification share a common bottleneck. We presented a masked
visual digit as T1, and high or low pitched auditory word as T2,
with targets separated by 150, 350, or 700 milliseconds.
Participants made a speeded pitch response to T2, and an unspeeded
response indicating T1 identity. The task-defined probability of T2
was manipulated to produce a P300 component. At short T1-T2
separations, T2 response slowing was observed, but, in contrast to
the PRP paradigm, corresponding P300 delays were also observed. We
conclude there are dissociable bottlenecks for stimulus
identification and response selection.
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