Regularity is not a key factor for encoding repetition in rapid image streams

Human observers readily detect targets and repetitions in streams of rapidly presented visual stimuli. It seems intuitive that regularly spaced repeating items should be easier to detect than irregularly spaced ones, since regularity adds predictability and in addition has ecological relevance. Here, we show that this is not necessarily the case, and we point out the intrinsic difficulty in addressing this question. We presented long RSVP streams of never-before-seen natural images containing repetition sequences; an image appearing six times interleaved by one or more non-repeating distractors, and asked participants to detect the repetitions and to afterwards identify the repeated images. We found that the ability to detect and memorize repeated images was preserved even with irregular sequences, and conclude that temporal regularity is not a key factor for detection and memory for repeating images in RSVP streams. These findings have implications for models of repetition processing.