COMBINING EXPECTANCIES

Five experiments examine the combined effects of spatial and non-spatial cues on the latency of an orientation judgement. In Experiment 1 an interaction between position and form expectancies is observed: There is an unusual delay in response time (RT) when expectancies mismatch-that is, when an unexpected (uncued) form appears at an expected (cued) position or an expected (cued) form appears at an unexpected (uncued) position. This interaction is inconsistent with the spatial spotlight model's prediction that position and form expectancy effects will be additive. The position-form interaction is eliminated when target position discriminability is made difficult by adding a distractor item at the location not containing a target (Experiment 2) or by decreasing the validity of the positional cue (Experiment 3). Decreasing the validity of the form cue has no effect on the interaction. The mismatching expectancy interaction is not unique to combinations of position and form-it is also observed when temporal (Experiment 4) and colour (Experiment 5) expectancies are combined with form expectancies. The effects of advance knowledge of position therefore suggest no special status for location compared to other stimulus attributes. Thus, at least for combined expectancies, the notion of a uniquely spatial mental spotlight seems unjustified. It is hypothesized that expectancy interactions may reflect a hierarchical crosstalk relation between dimensions of encoding.