Influence of bias on visuospatial and verbal compatibility effects in mixed-mapping environments

The advantage for the compatible mapping of physical locations or arrows to keypresses is reduced when trials with compatible and incompatible mappings are mixed, whereas the advantage is increased for location words. We evaluated explanations of these mixing effects by varying the proportions of compatible and incompatible trials for groups performing with each stimulus mode. The mappings were compatible on 75%, 50%, and 25% of the trials, respectively, for compatibly biased, unbiased, and incompatibly biased conditions. For locations and arrows, compatible bias increased the SRC effect, and incompatible bias reduced the effect; for location words, the incompatible bias was stronger than the compatible one. Reaction time distributions showed that, with locations and arrows, initial activation toward either the compatible (unbiased condition) or the predominant (biased conditions) response was transient. With words, activation of the corresponding response increased across the distribution, regardless of bias condition. The influence of bias on the SRC effects was relatively independent of the mixing and sequential effects, and was different for words than for nonwords. These results are consistent with the view that visuospatial stimuli produce transient activation of the corresponding or predominant response, whereas location words produce phonological activation, required for word identification, that persists.