Magnitude versus parity in numerical judgements: Event-related brain potentials implicate response conflict as the source of interference

When subjects make 'odd/even' and 'low/high' decisions about digits, information about the digit's magnitude can interfere with the decision about the digit's parity. The present experiment used a psychophysiological approach to examine whether this interference arises at the level of response processing. Subjects performed a choice-reaction time task involving low/high and odd/even judgements about the digits 2 through 9. The data point to a response locus for the interference effect with the size of the effect being dependent on the ease with which magnitude information can be used to prime the appropriate response. This, in turn, is influenced by the 'naturalness' of the mapping between magnitude and response hand as well as by the distance of a digit to the low/high cut-point.