Combined expectancies: electrophysiological evidence for the adjustment of expectancy effects.
BACKGROUND
When subjects use cues to prepare for a likely stimulus or a likely response, reaction times are facilitated by valid cues but prolonged by invalid cues. In studies on combined expectancy effects, two cues can independently give information regarding two dimensions of the forthcoming task. In certain situations, cueing effects on one dimension are reduced when the cue on the other dimension is invalid. According to the Adjusted Expectancy Model, cues affect different processing levels and a mechanism is presumed which is sensitive to the validity of early level cues and leads to online adjustment of expectancy effects at later levels. To examine the predictions of this model cueing of stimulus modality was combined with response cueing.


RESULTS
Behavioral measures showed the interaction of cueing effects. Electrophysiological measures of the lateralized readiness potential (LRP) and the N200 amplitude confirmed the predictions of the model. The LRP showed larger effects of response cues on response activation when modality cues were valid rather than invalid. N200 amplitude was largest with valid modality cues and invalid response cues, medium with invalid modality cues, and smallest with two valid cues.


CONCLUSIONS
Findings support the view that the validity of early level expectancies modulates the effects of late level expectancies, which included response activation and response conflict in the present study.
Mattler
Uwe
U
Department of Neurology II, Center for Advanced Imaging, Otto-von-Guericke-University Magdeburg, Leipziger Strasse 44 (Haus 1), D-39120 Magdeburg, Germany. Uwe.Mattler@Medizin.Uni-Magdeburg.DE
van der Lugt
Arie
A
Münte
Thomas F
TF