We are looking at the effect of reducing the SOA on rt2. Parallel processing would result in rt2 remains constant with a decrease of SOA A Bottleneck would result in rt2 increases with a decrease of SOA PRP effects show up when the latter is true.
Suggestion is that extremely high compatibility is also required.
PRP has been found to reduce with extensive practice. However when subjects were required to respond when the SOA was changed, then delay in responding to the second signal rose to 50msec. Experimenters like Pashler have sought to find the locus of the effect. Most widely accepted view is that the PRP effect is one of a bottleneck in response selection. Selection of the second response cannot begin until the first response is selected.