**Exclusion Criteria** Subject data will be excluded on the following grounds: * Subjects reported being under 18 years of age. * Subjects reported problems with experimental playback, such as stuttering, freezing (pre-determined options) or another issue specified in a free-response. A coder who is blind to the condition assignment will examine these open-ended responses to determine whether or not the subject should be excluded. When the response is ambiguous, their data will be excluded. * Subjects reported needing correction to their vision but not wearing it during the experiment. * Subjects reported counts that err by more than 50% in either direction more than once. * Subjects reported failing to notice the "unexpected object" after a full-attention trial or misidentified its shape or color. * Subjects reported having performed a similar task before, wherein they tracked multiple objects and something unexpected appeared. If subjects reported participating in a smiliar task, an independent coder will examine their descriptions of prior experience to determine whether the subject should be excluded. * Subjects failed to answer any question during the course of the experiment. **Measures** <br> After each trial in which no unexpected object appears and after the critical trial, we will collect subjects' counts of how many times the attended objects bounced off the edge of the frame. On the critical trial and the full-attention trial, we will ask whether subjects noticed an object other than the squares or checkerboards, and then ask them to describe the shape and color from a menu of pre-determined options. Subjects will be counted as having noticed the object only if they affirm having seen something new and correctly identify either its shape, color, or both. <br> We will also collect a set of demographic data for exclusion purposes, as well as characterizing our sample. **Analysis** <br> The predicted patterns of the data under the two hypotheses--that similarity to the attended object matters for noticing rates, or that difference from the ignored object matters--allow us to test which hypothesis is the best fit by conducting two tests: 1. If similarity to the attended set modulates noticing rates, then when subjects attend to the white squares, they should notice the white unexpected object (i.e. the more similar one) **more than** the black unexpected object. Thus, the difference in noticing rates (noticing white - noticing black) should be positive. 2. If dissimilarity from the ignored set modulates noticing rates, then when subjects attend the checkerboards, they should notice the white unexpected object (i.e., the one most similar to the ignored items) **less than** the black unexpected object. Thus the difference in noticing rates (noticing white - noticing black) should be negative. For each test, we will determine the difference in noticing rates for each condition and will compute a 95% confidence interval around that difference. If the difference score is positive for attending white squares and not different from zero for the checkerboards, it supports the similarity-to-attended hypothesis. If the difference score is negative for the checkerboards and not different from zero for the white squares, it supports the difference-from-ignored hypothesis. Other patterns would suggest other mechanisms at work.