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Christopher A. Dickinson, Gregory J. Zelinsky; The “flicker” search task: A paradigm for investigating memory in visual search. Journal of Vision 2002;2(7):539. doi: 10.1167/2.7.539.
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© ARVO (1962-2015); The Authors (2016-present)
Following Horowitz and Wolfe (1998), observers searched for an oriented T among oriented Ls under static (standard search) and dynamic (items randomly relocating) viewing conditions. We modified these conditions by embedding both search tasks in a “flicker” display paradigm. Static and dynamic trials consisted of a repeating sequence of fifteen 72 ms stimulus frames, each separated by a gray field. In addition to making the static displays more visually comparable to the dynamic (e.g., by controlling for onset/offset noise, etc.), this presentation method also enabled memory to be assessed during search by varying the duration of the gray masking field (i.e., the ISI). A memoryless model of search would assume that processing stops with each display offset, making each new display a new search task. Such a model would therefore predict a decrease in search efficiency with longer ISIs, with both static and dynamic tasks being affected equally. A memory-based model would predict an attenuated effect of ISI in the static condition due to processing continuing into each masking interval and accumulating over frames. We tested these predictions for static and dynamic search using three ISIs (101, 402, and 703 ms), three set sizes (9, 13, and 17 items), and two target conditions (present vs. absent). Consistent with a memoryless model, search slopes increased with ISI in the dynamic condition. A far smaller effect of ISI was found in the static slopes, a pattern more consistent with a memory-based model. We can therefore conclude that search is exploiting processing occurring on a “remembered” display. Although longer ISIs afforded a greater opportunity for processing in both static and dynamic conditions, information resulting from this processing could only accumulate across the static displays. Because items in the dynamic condition were shifting locations, processing extending into the ISI would often be wasted upon presentation of the next dynamic frame.
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