We studied how attention affects contrast detection performance when the ta
rget is surrounded by mask elements. In each display quadrant we presented
a hexagon of six vertical Gabor patches (the 'surround'). Only one of the h
exagons contained a central Gabor patch (the 'target') and the task was to
report that quadrant (spatial four-alternative-forced choice). Attention wa
s manipulated by means of a double-task paradigm: in one condition observer
s had to perform concurrently a central letter-discrimination task, and the
contrast-detection task was then only poorly attended, while attention was
fully available in the other condition. We find that under poorly attended
conditions targets can be detected only when the target contrast exceeds t
he surround contrast (contrast popout) or when the target orientation diffe
rs from the surround orientation by more than 10-15 degrees (orientation po
pout). When the target orientation is similar to the surround orientation,
attention can reduce the contrast detection thresholds in some cases more t
han four-fold, demonstrating a very strong attentional effect. (C) 2000 Els
evier Science Ltd. All rights reserved.