Sequence Learning Is Surprisingly Fragile in Visual Search

Extensive research has shown that people are sensitive to statistical regularities of visual stimuli, such as a repeated sequence of object locations. Such learning, however, has primarily occurred for objects presented in isolation. Here, we tested whether sequence learning also manifested in complex displays. Using variants of the serial reaction time task, we asked participants to report the screen quadrant of a letter T, whose location followed a 12-trial sequence that repeated 30 times over 360 trials. In different experiments, we manipulated the nature of distractors surrounding the target. The T could appear in isolation, as a color singleton among distractors with fixed or variable locations, or as a conjunction search target. Sequence learning—expressed as elevated response time when the learned sequence was disrupted—decreased as spatial noise increased. Learning was robust when the T appeared in isolation or when it was surrounded by distractors that did not change locations. It was reduced in feature searchand eliminated in conjunction search. These findings suggest that target locations are coded in relation to concurrently presented distractors. Variability in distractor locations disrupts target location sequence learning, revealing a limit to people’s ability to extract and use spatiotemporal regularities in complex environments