Abstract
Driven by considerations arising from studies in hemiplegic patients, we examined how the insertion of rare n-response trials affects motor preparation studied in S1-S2 paradigms. Results for the motor priming task (experiment 1) showed that for response-requiring conditions the 'validity effect' was conserved for behavioural and ERP indices. For the no-response condition, foreperiod activities were similar to neutral trials suggesting motor preparation in both conditions and hence preparation for the unlikely event. A second experiment with fully predictive primes showed no evidence for movement preparation processes in no-response trials. These findings suggest different strategies for the anticipation of likely responses compared to likely events that don't require a response.