Repetition violating events do not enhance sensitivity to embedded content, but repeated events can reduce sensitivity.

Oddball paradigms involve the presentation of sequences of repeated events that are broken by a novel "oddball." These have been used to examine the neural and perceptual consequences of predictive processes in the brain. Two intriguing perceptual findings are that people are more sensitive to visual content embedded in oddballs and that people perceive oddballs as longer lasting-relative to repeated events. Recent investigations have looked at the possibility that fluctuations in attention during presentation sequences might impact perception though. Because the number of repeated "standards" (that do not require a behavioral judgment) seen before a "test" (which can require a behavioral judgment) is often circumscribed, as more standards are encountered, the probability of a further standard decreases, whereas the probability of a test increases. So, later tests can be anticipated, whereas early tests are improbable. It has been shown that when all tests can be anticipated, and all tests are equally likely to be a further repeated standard or an oddball, oddballs still seem longer lasting than repeats. Here we show that the same conditions undermine the visual acuity advantage for oddball content. Our experiment clarifies that this increase in acuity for oddballs results from a degradation of acuity to repeat tests that cannot be anticipated. We found that people's pupils tended to dilate as they expected a test, consistent with top-down attention scaling with test probability. In a second experiment, we replicated the time perception difference and the lack of visual acuity difference under the same experimental conditions. (PsycInfo Database Record (c) 2025 APA, all rights reserved).