Academic journal article Psychonomic Bulletin & Review

Prioritizing New Elements with a Brief Preview Period: Evidence against Visual Marking

Academic journal article Psychonomic Bulletin & Review

Prioritizing New Elements with a Brief Preview Period: Evidence against Visual Marking

Article excerpt

Watson and Humphreys (1997) have proposed that the ability to prioritize new elements over old elements involves a time-consuming process (of at least 400 msec) of active inhibition of the locations of the old elements, which they referred to as visual marking. Recently, Donk and Theeuwes (2001) have suggested that prioritized selection of new over old elements is an instantaneous process related to the luminance change accompanying the appearance of the new elements. The aim of the present study was to test these two alternatives by investigating whether prioritized selection of new over old elements could be achieved with a very short preview of the old elements (50 msec). The results indicated that participants were able to prioritize selection of new over old elements when the new elements were presented with luminance onset whereas the old elements were not. New elements could not be prioritized if both the old and the new elements appeared with luminance onset. The results indicated that prioritization of new elements is based on an instantaneous process, rather than on a time-consuming process.

Watson and Humphreys (1997) have proposed that people have a mechanism for prioritizing the selection of new events or objects over old ones. This mechanism, referred to as visual marking (see also Theeuwes, Kramer, & Atchley, 1998; Watson & Humphreys, 1997), is assumed to operate through top-down attentional inhibition applied to the positions of old stimuli. Evidence for the ability to prioritize new over old elements stems from experiments in which the preview paradigm has been used. Thus, Watson and Humphreys set up three conditions: a conjunction search task, in which participants had to detect a blue letter H target between green Hs and blue As; a feature search task, which was essentially the same as the conjunction search task, except that no green distractors were presented (therefore, the display size was half that of the conjunction search task); and a preview condition, in which first the green Hs (i.e., the old elements) were presented and, after 1,000 msec, the blue As were added to the display, with or without the blue H target (i.e., the new elements). Watson and Humphreys found that slopes in the preview condition were identical to those obtained in the feature search condition and different from those obtained in the conjunction search condition. This difference between the slopes obtained in the preview condition and those obtained in the conjunction search condition, denoted as the preview effect, was taken as evidence that, with a preview, observers can prioritize the selection of new over old elements.

Even though the preview effect indeed shows that observers are able to prioritize the selection of new over old elements, it is unclear whether this ability truly is the result of a process in which the old elements are deprioritized during the preview, as was suggested by Watson and Humphreys (1997). Alternatively, it might be that new elements can be directly prioritized due to the sudden luminance onset accompanying their appearance (Yantis & Jonides, 1984). Indeed, Donk and Theeuwes (2001) have shown that if new elements appear without luminance change (e.g., if the elements are equiluminant with the background), the new elements can no longer be prioritized, suggesting that prioritized selection might not be due to top-down inhibition of old objects, as was suggested by Watson and Humphreys. Possibly, observers are able to directly prioritize the selection of new elements by the luminance onsets accompanying their appearance (see also Donk & Theeuwes, 2003).

Both an inhibition account, as proposed by Watson and Humphreys (1997), and an onset account, as advocated by Donk and Theeuwes (2001), can explain the preview effect. Nevertheless, these explanations differ fundamentally from each other. Whereas an inhibition account assumes that observers are involved in an active process of inhibiting the locations of the old elements during the preview, the onset account basically presumes no observer involvement prior to the appearance of the new elements. …

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