Eimer, M., & Coles, M.G.H. (2001). The lateralized readiness potential. In M. Jahanshahi & M. Hallett (Eds.). The Bereitschaftspotential: In Honour of Professors Deecke and Kornhuber. New York: Kluwer Academic / Plenum (forthcoming).
INTRODUCTION: The pioneering work of Kornhuber and Deecke on the Bereitschaftspotential (Kornhuber & Deecke, 1965) suggested that movement-related brain activity could be recorded from the scalps of human subjects. Not only did this open up the possibility of studying brain-movement relationships using non-invasive procedures, it also pointed to a method by which measures of event-related brain potentials (ERPs) could be used to study cognitive processes. The benefits of the discovery of the Bereitschaftspotential for the analysis of cognitive function were not perhaps as obvious as those that related to the discovery of other ERP components during the 1960s, such as the P300 (Sutton, Braren, Zubin, & John, 1965) and the CNV (Walter, Cooper, Aldridge, McCallum, & Winter, 1964). Nevertheless, it has become clear in the last 35 years that the impact of its discovery has been just as profound. This is because knowledge of covert movement-related processes has proved to be extraordinarily important in exploring human cognitive function.
Models of the structure and dynamics of cognition propose the existence of cognitive processes which function to produce a given behavioural output, usually as a consequence of some input. The problem confronted by the cognitive psychologist is how to evaluate claims about the nature and mode of operation of these processes when the data available are limited to parameters of the output, such as speed and accuracy. It is the problem of making inferences about covert processes from observations of overt behaviour. In this regard, what was so striking about the studies of Kornhuber and Deecke, and those by Vaughan and his colleagues (Vaughan, Costa, & Ritter, 1968) which followed shortly thereafter, was that brain activity could be detected prior to an overt movement, and that the nature of this activity seemed to depend on the nature of the impending movement. The Bereitschaftspotential begins several hundred ms before the movement and, as the time for movement approaches, the scalp distribution depends on what movement is about to be executed.
It was the latter observation that gave rise to the measure called the lateralized readiness potential (LRP). With the studies of Kornhuber and Deecke (1965) as a starting point, Kutas and Donchin (1980) had examined movement-preceding brain activity for a variety of conditions which differed in terms when subjects knew which of two manual responses they would have to make. Kutas and Donchin found that the time at which the brain activity became asymmetrical was closely related to the time at which subjects knew whether a right or left-hand response would be required, and concluded that the asymmetry reflected preparation to execute specific motor acts.
On the basis of these results, groups in Groningen (e.g. Smid, Mulder, & Mulder, 1987) and Illinois (e.g. Coles & Gratton, 1986) simultaneously and independently reasoned that, under certain circumstances, the presence of asymmetries could be used to infer the presence of preferential preparatory activity. They proposed procedures to derive a measure of asymmetric, movement-related brain activity and these procedures yielded the measure now referred to as the LRP (although it was originally referred to as "corrected motor asymmetry" by the Groningen group).