Time-course of spatial-attentional focusing in the case of high processingdemand on the peripheral precue

Subjects had to identify pairs of spatially overlapping or neighbouring let ters exposed successively at various locations around the central fixation. The first letter (S1) in a pair acted both as a physical precue to indicat e the S2 location and as a stimulus letter to be identified. The second let ter (S2) in a pair acted only as a letter to be identified. The SOA was var ied between 0 and 320 ms in different experiments. Comparison of the time-c ourse functions of S2 identification in the conditions of (1) single pair p resentation and (2) presentation of the letter pairs in the context of dist racter letters that accompanied S2 in time, but occupied alternative spatia l positions, revealed that S2 processing from the covert spatial-attentiona l focus was open to non-decreasing interference from the distracter letters up to 240 ms SOAs. An unexpected result consisted in equal level of S2 ide ntification regardless of whether S1 had to be identified or not. This show s that if the peripheral precue has to be processed with higher processing demands at the identification level beyond simple location processing (whic h by itself is sufficient to fulfil the spatial orienting function), then t he narrowing down or zooming-in of the attentional area in response to a ph ysical precue can take place as effectively as in the case of a lesser proc essing demand on that precue. By comparing the relative time-course functio ns of S1 and S2 identification, it was found that S2 identification gained significant advantage over S1 identification at intermediate SOAs even if t he intensity of S1 exceeded that of S2. The results of this investigation r efer to the spontaneous, automatic nature of spatial attentional focusing t hat is evoked by spatially localised transient signals, but also to the pos sibility of interference between the targets and distracters in the working memory representation.