Investigating stimulus salience and perceptual load interaction using a Hybrid Visual Search-flanker Task

Abstract

The perceptual load theory of selective attention proposed by Tsal and Lavie (1994) and Lavie (1995) argues that selective attention is predominantly necessitated by perceptual capacity limitations. In order to account for the experimental evidence where stimuli are attentionally selected either early or late, Lavie (1995) proposed that early selection occurs when perceptual capacity has been reached, while late selection occurs when perceptual capacity has not been reached. This effect has been demonstrated with the use of hybrid visual-search flanker search tasks on numerous occasions (Lavie, 2004). However, some researchers argue that the selection of stimuli is attributable to salience and not to perceptual load. Due to the increased salience of flankers in low perceptual load trials the distractor identity is much more readily processed, thereby leading to the distractor interference. Lavie (1995) attributes the increased distractor interference in low perceptual load trails to the automatic allocation of spare perceptual resources; a process that is mediated by perceptual load levels. This study investigates the potential interaction between perceptual load and distractor salience by presenting 20 participants with a hybrid visual-search flanker task, but placing salient colour singletons distractors in half the trials. The results indicate that the compatibility effect is largely nullified in low perceptual load trials containing salient distractors. The non-salient distractor trials, however, produced a significant compatibility effect as predicted by the perceptual load theory of selective attention. The lack of a significant compatibility effect in salient distractor trials might be an indication that top-down attentional control mechanisms can capitalise on the task-irrelevant colour feature to suppress the processing or perception of the distractor. This finding problematises the hypothesis that the automatic spill-over of perceptual capacity is responsible for the distractor interference in low perceptual load trials as necessitated by perceptual load theory.