Abstract
Background: Covert attention improves discriminability and accelerates the rate of visual information processing (Carrasco & McElree, 2001). Transient (exogenous) attention is argued to have a more automatic effect on processing, whereas sustained (endogenous) attention is argued to be a more flexible mechanism. We evaluated the respective automaticity and flexibility of exogenous and endogenous cues, using a response-signal speed-accuracy trade-off (SAT) procedure to investigate whether discriminability and rate of information processing differ as a function of cue validity. The SAT procedure maps the full time-course of processing and enables conjoint measures of discriminability and speed of information processing. Methods: Observers performed an orientation discrimination task in which a location cue (67 ms exogenous peripheral cue; 150 ms endogenous central cue) preceded a target (by 53 ms and 150 ms, respectively) presented with 0 or 7 distracters. The target appeared in one of 8 iso-eccentric locations (4 eccentricity). The location cue varied in validity from 12% (chance level) to 100%. A response tone sounded after one of 7 lags (ranging from 40 to 2000 ms) to prompt observers to respond. Trials were blocked by cue type (exogenous/neutral vs. endogenous/neutral) and cue validity (% valid and invalid trials). Observers completed 10 sessions per cue type (exogenous and endogenous) and were always informed of the cue validity. Results & Conclusion: With exogenous cues, the valid-cue benefits and the invalid-cue costs in both discriminability and processing speed were comparable across the range of cue validities. However, with endogenous cues, the observed benefits and costs both increased with cue validity. These results provide compelling time-course evidence that transient attention is automatic, but sustained attention can be flexibly allocated in a manner that increases the benefit of the valid cue and decreases the cost of the invalid cue.
NSF #BCS 9910734/HCP