Controlling for dilution while manipulating load: Perceptual and sensory limitations are just two aspects of task difficulty

Lavie and de Fockert (2003) proposed that perceptual load and sensory limitations reflect two distinct mechanisms producing opposite effects: Perceptual load eliminates distractor interference, whereas sensory limitations enhance it. Tsal and Benoni (2010a) suggested that these results may have been due to the confounding effect of dilution--that is, to the presence (perceptual load) or absence (sensory load) of neutral items capable of diluting distractor interference. In the present study, we jointly manipulated dilution with perceptual load and with sensory degradation. The results show that, with both perceptual and sensory manipulations, the presence of diluting items eliminates distractor interference, whereas controlling for dilution increases distractor interference. We therefore conclude that perceptual and sensory limitations are just two aspects of task difficulty.