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Heeyoung Choo, Steve Franconeri; Hemifield modulation of approximate number judgments. Journal of Vision 2010;10(7):1207. doi: 10.1167/10.7.1207.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system offers several types of summary information about visual features, including approximate number (Miller & Baker, 1968). Approximate number perception can be affected by adaptation in a hemifield specific manner (Burr & Ross, 2008; but see also Durgin, 2008). After adapting to a large and a small number of dots in different hemifields, a later presentation of identical sets of dots appears to have the opposite relationship (smaller and larger, respectively). This result raises the possibility that numerosity information is extracted independently over each hemifield. We directly tested this possibility by asking participants to judge the larger of two collections of dots, one presented across the hemifield boundary (between-hemifield presentation) and the other presented within one of the hemifield (within-hemifield presentation). The between- or within- hemifield manipulation was made by keeping the dot collections in the same locations, but then changing fixation location. Participants systematically judged the within-hemifield collections as having more dots. However, this effect disappeared when (1) the fixation location was manipulated so that neither collection fell on the hemifield boundary, and (2) the two collections were presented sequentially. In other words, any hemifield modulation in numerosity judgments occurred only when a subset of dots crossed the hemifield boundary. The results together suggest that when creating an approximate number representation, dots falling in the same hemifield are to mandatorily pooled.
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