HOW DOES PERCEPTUAL LOAD DIFFER FROM SENSORY CONSTRAINS? TOWARD A UNIFIED THEORY OF GENERAL TASK DIFFICULTY
Load theory of attention stipulates that distinct attentional mechanisms underlie the effects of perceptual load and sensory degradation on search performance. Such distinction mainly relies on the finding that increasing perceptual load reduces distractor interference whereas increasing sensory degradation magnifies distractor interference (Lavie & DeFockert, 2003). We propose instead that the two types of load highlight different aspects of general task difficulty. We claim that the different patterns of results are due to the fact that increasing perceptual load has typically entailed the addition of neutral items capable of diluting distractor interference (Benoni & Tsal, 2010; Tsal & Benoni, 2010), whereas increasing sensory load has not. In the present experiment we jointly manipulated dilution with each type of load. Similar results were obtained for the two types of load: when dilution was controlled, increasing task difficulty increased distractor interference, but the addition of potential diluters reduced all types of distractor interference.