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Summer L. Sheremata, David C. Somers; Role of encoding duration on visual-short term memory capacity. Journal of Vision 2008;8(6):1173. doi: 10.1167/8.6.1173.
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Visual short-term memory (VSTM), which has a capacity of approximately four objects, is a key bottleneck in our visual perceptual abilities. However, it remains unclear which processes govern the limited capacity of VSTM. Memory is traditionally described in terms of the processes of encoding, maintenance/storage, and retrieval. It has been proposed that capacity limits are not the result of encoding limitations, but rather reflect a fixed number of “stores” (Vogel, Woodman, & Luck 2001). In the present study we have investigated the influence of encoding on VSTM performance. Subjects were asked to perform a visual short-term memory task in which colored squares were presented for either 100 or 500 ms. Performance improved across a range of set sizes with longer stimulus presentations. Furthermore, K scores reached a plateau at 5 rather than 4 objects when stimulus durations were increased to 500 ms. In order to limit possible effects of verbalizing, we investigated the role of encoding duration in a second paradigm in which subjects were asked to detect a 20 degree change in orientation of a luminance-defined gabor which was presented for either 200 or 1000 ms. In this paradigm, performance again improved for longer encoding durations. These results confirm the view that maintenance provides a major limit to VSTM capacity, but also demonstrate that encoding can have a strong impact on VSTM capacity. These results serve as an important caveat for researchers studying VSTM mechanisms.
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