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Shahab Ghorashi, Lisa N. Jefferies, Vincent Di Lollo; Expansion and contraction of the attentional focus is influenced by top-down factors. Journal of Vision 2008;8(6):141. doi: 10.1167/8.6.141.
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Jefferies and Di Lollo (2007) proposed a spatiotemporal model in which the focus of attention shrinks and expands linearly over space and time. Exogenous factors such as stimulus contrast and luminance are known to influence the rate of this modulation (Jefferies, Enns, & Di Lollo,2007). Do endogenous factors also influence that rate? Although there are some hints to this effect (Ghorashi et al., 2003), this issue has not been studied directly. We adopted Jefferies and Di Lollo's paradigm in which Lag-1 sparing is used to index the spatial extent of the focus of attention. When two sequential targets are inserted in a rapid stream of distractors, perception of the second target is impaired at short inter-target lags (AB deficit). Paradoxically, this deficit is not obtained when the second target appears directly after the first (Lag-1 sparing). In the current study, two streams - one of random-dot patterns, the other of random digits - were presented one on either side of fixation. The first target (a letter) appeared unpredictably either in the dot-stream or in the digit-stream, and the second target (another letter) appeared - again unpredictably - in either the same stream as the first or in the opposite stream. To monitor the rate of shrinking of the attentional focus, we varied the SOA between successive items in each stream. The condition of principal interest was when the targets appeared in different streams: if endogenous factors play a role, it should be more difficult to disengage attention from the meaningful (digit) stream than from the meaningless (dot) stream. If so, we expected greater Lag-1 sparing when the second target appeared in the digit stream because attention was still engaged in that location. The results confirmed this expectation, strongly suggesting that top-down factors influence the shrinking and expanding of the attentional focus.
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