The lateralized readiness potential as an on-line measure of automatic response activation in S-R compatibility situations

Abstract

The Lateralized Readiness Potential (LRP) is an electrophysiological indicator of partial response activation. A number of experiments are reported in which the LRP was measured in order to obtain evidence for automatic response activation processes elicited in S-R compatibility situations. In the first series of experiments, a cue-target paradigm was employed, and the LRP was measured in response to the cue. When arrows were used as cues, and early activation of the response corresponding to the arrow's direction was observed, which was largely independent of objective cue-response contingencies, presumably indicating an involuntary process. No such effect was observed when nonspatial cues (colored squares) were used or when the cue was unattended. A second series of experiments was conducted to demonstrate that due to systematic confounds of motor and nonmotor asymmetries, LRPs elicited by lateralized target stimuli cannot be interpreted unequivocally in terms of response activation. Therefore, an alternative paradigm is introduced in which colored arrows are used as target stimuli, with arrow color relevant and arrow direction irrelevant for response selection. The LRPs revealed an early activation of responses spatially congruent to the arrow's direction. Overall, the experiments show that when the various confounds of motor and nonmotor effects on the LRP are dealt with effectively, the LRP may be a useful tool for studying automatic response activation processes in S-R compatibility situations.