Expecting different categories at different locations and spatial selective attention

An experiment is reported testing the idea that spatial selective attention operates like the beam of a spotlight. Subjects made speeded orientation judgements to alphanumeric characters that could appear at an upper or lower display location. Letters tended (p = 0.8) to occur at one location, while digits tended to occur at the other. Alphanumeric category was pre-cued (p = 0.8). Response times were faster for cued than uncued items. For cued items subjects were faster at the likely location for a cued item. For uncued items this was reversed, with faster responding at the likely location for an uncued item. Hence, location selectivity reflected location probability for each category regardless of short-term expectancy concerning stimulus category. These data are incompatible with a simple spotlight view of spatial selective attention. Alternative explanations, including a modified two-stage spotlight model, were considered.