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Harry Haladjian, Asha Griffith, Zenon Pylyshyn; The attentional blink impairs localization but not enumeration performance in an “enumerating-by-pointing” task. Journal of Vision 2011;11(11):201. doi: https://doi.org/10.1167/11.11.201.
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Earlier we reported (Haladjian & Pylyshyn, 2010) that observers are able to rapidly and accurately enumerate up to six items when using an “enumerating-by-pointing” method (compared with the typical subitizing limit of four). We have been exploring possible reasons for this increase. The present study examines the role of increased encoding time (without increasing actual viewing time) by testing whether two presentations of the stimulus separated by a variable interval improves enumeration performance. Additionally, this allowed us to test if the second presentation of the stimulus was sensitive to the attentional blink. Participants were shown masked displays that contained 2–9 randomly-placed black discs (~1° diameter) on a gray background. The stimulus was presented once for 100-ms or presented twice for 50-ms (each) with a delay of 200-, 400-, or 600-ms (ISI) between the mask offset and the second presentation onset. Participants then marked the locations of each disc using a computer mouse.
Trials with two separate 50-ms presentations showed better enumeration performance than trials with a single 100-ms presentation for numerosities >4; the delay conditions did not significantly differ from each other (except in 5-item displays). For localization performance, two-presentation trials produced more accurate responses than single-presentation trials for numerosities <7. Here, location accuracy was significantly better in the 600-ms delay condition for displays with 5–8 items. This suggests an additive benefit when presenting the second display outside of the attentional blink in trials where observers needed to enumerate >4 items. These results (that the attentional blink affects localization more than enumeration) suggest that attention is more critical for the encoding of location information than for enumerating small sets. These results also point to the possibility that the increased coding time associated with the mouse pointing (when marking object locations) may play some role in the increased subitizing limit.
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