Abstract
The theory of perceptual load (Lavie & Tsal, 1994; Lavie, 1995) proposes that the processing of irrelevant distractors is prevented only when high load in relevant processing exhausts attentional resources. The theory has been supported by a line of experiments presenting conditions of high and low-load in separate blocks, resulting in processing of to-be-ignored stimuli in the low load condition but not in high load conditions.
Theeuwes, Kramer, and Belopolsky (2004), showed that when high-load and low-load displays are randomly intermixed, the processing of to-be-ignored stimuli is similarly obtained under both conditions, suggesting that: 1) attentional sets affect selectivity 2) high perceptual load is not sufficient for effective selectivity.
Recently, Tsal and Benoni (2010; Benoni & Tsal, 2010) argued that the common use of display size confounds perceptual load with the factor of dilution (produced by the neutral items present in high load displays). In a series of experiments which separated the possible effects of load and dilution, they demonstrated that it is dilution, not load, affecting the efficiency of selection.
The results obtained in Theeuwes at el., 2004 questions perceptual load theory but also challenges the dilution account, which offers an alternative underlying bottom-up mechanism.
In the present study we separated the effects of dilution and load by adding dilution displays, that were low in perceptual load but high in dilution, we tested the influence of attentional sets, by comparing mixed and fixed blocks for low-load, high-load, and dilution displays. We found that attentional sets interacted with load but not with dilution. Thus, the dilution effect is preserved across fixed and mixed presentations and is not influenced by expectancy of trial type. The results are discussed within the framework of a new general task difficulty account.
Meeting abstract presented at VSS 2012