bottom-up and top-down attention: different processes and overlapping neural systems
Page 2Attention’s effects on brain and behavior. a (Left) Pop-out (bottom-up) search task. Target differs from distractors in a single salient feature (color singleton); (below) Reaction time (RT) does not increase with number of distractors (set size). (Middle) Conjunction (top-down) search task without cueing. Target differs from distractors based on a conjunction of features (color and shape); (below) RT increases with set size. (Right) Conjunction search task with central (top-down) cue indicating location of target; (below) RT increases marginally with set size. b (Left) Schematic of neuronal firing in visual and attentional areas when the neuron’s receptive field (RF, dashed black oval, upper panel) contains a non-salient stimulus (lower left panel and blue trace) versus a salient stimulus (lower right panel and purple trace). (Middle) Same as in the left panel, but when a top-down cue is used to direct attention to a stimulus within its RF (lower left panel and blue trace) versus outside the RF (lower right panel and purple trace). (Right) Same as in the left panel, but when a distractor is present along with the target in the neuron’s RF. The suppression of activity caused by the distractor (lower left panel and blue trace) can be alleviated by directing attention specifically to the target (lower right panel and purple trace). c (Left) Posner cueing paradigm. Fixation is followed by the appearance of a cue. The cue can be a central or top-down cue (arrowhead, upper panel), a neutral cue (middle panel) or a peripheral or bottom-up cue (transient flash, lower panel). This is followed by the appearance of the stimulus, after a brief delay. Subjects have to detect the presence, identify or localize the target stimulus, which may appear on the cued side (validly cued trials) or not (invalidly cued trials). (Right, upper) Reaction times typically decrease with increasing target strength (e.g., stimulus contrast). The reaction times are highest for invalidly cued trials, intermediate for neutrally cued trials, and least for validly cued trials. (Right, lower) Accuracy (% correct) is typically least for invalidly cued trials, intermediate for neutral cues and highest for validly cued trials. d Important nodes in frontal and parietal cortex involved in attention. Areas in blue are primarily involved in top-down control of attention, but also activate, albeit less strongly, during bottom-up attention. Areas in red are primarily implicated in bottom-up, stimulus-driven reorienting (abbreviations expanded in main text). |