Temporal target integration underlies performance at Lag 1 in the attentional blink

When two targets follow each other directly in rapid serial visual presentation (RSVP), they are often identified correctly but reported in the wrong order. These order reversals are commonly explained in terms of the rate at which the two targets are processed, the idea being that the second target can sometimes overtake the first in the race toward conscious awareness. The present study examined whether some of these order reversals might alternatively be due to a mechanism of temporal integration whereby targets appearing closely in time may be merged into a single representation. To test this integration account, we used an attentional blink task in which the two targets could be combined perceptually in a meaningful way such that the conjunction of the two target elements constituted a possible target stimulus itself. The results showed that when targets appeared at Lag 1, observers frequently reported seeing only a single merged target stimulus, and these reports occurred up to approximately three times as often as (real) order reversals. When the possibility to report the integrated percept was removed, order reversals consequently tripled. These results suggest that integration may actually be the primary cause of order reversals in dual-target RSVP tasks.