Fast trial pacing in a lexical decision task reveals a decay of automatic semantic activation

We report an experiment showing that reducing attentional resources by presenting trials with a short, 400 ms intertrial interval (ITI) (a) did not affect semantic priming at a 160 ms prime-to-target stimulus-onset asynchrony (SOA), relative to a 2500 ms ITI, and (b) eliminated the priming that occurred at a 1200 ms SOA when the ITI was 2500 ms. However, the elimination of priming at the 1200 ms SOA occurred only when the relatedness proportion (RP, proportion of related primes and targets) was .25 and not when it was .75. We interpret these results as showing that attentional/strategic priming occurs with an RP as low as .25, but only when sufficient attentional resources are available. Equally important, this is the first direct evidence that automatic semantic activation decays within 1200 ms in the standard semantic-priming/lexical-decision paradigm when attentional resources are not being used to maintain the goal of sustaining prime activation. We further argue that the frequent occurrences of related primes and targets with a high RP serve as reminders to maintain that goal such that cognitive load does not reduce long-SOA priming when the RP is high.