Voluntary attention reliably influences visual processing at the level of the C 1 component : a commentary on Fu , Fedota , Greenwood , & Parasuram ( 2010 )

The load theory of selective attention (Lavie, 1995; Lavie, 2005; Lavie and Tsal, 1994) assumes an adaptive filtering mechanism that suppresses irrelevant perceptual information depending on the amount of attentional or perceptual resources used for task-related goals. In the wake of the original findings of Lavie and co-workers (Lavie, 1995; Lavie and Tsal, 1994), different types of load were identified. For example, it is now common to distinguish between perceptual load on the one hand and attentional load on the other. Perceptual load can be defined in terms of the amount of stimulus information that needs to be processed to perform a given task. It is typically assessed by comparing experimental conditions in which increasing numbers of stimuli are presented, leading to increased task difficulty (e.g. Barnhardt et al., 2008; Handy et al., 2001). By contrast, attentional load can be defined as differences in processing demands in the absence of physical stimulus differences (e.g. Bahrami et al., 2007). This is usually assessed using task instructions that lead to different processing demands for the same stimuli, such as the comparison between color detection and detection of conjunctions of color and shape during serial visual presentation of the same stimuli (Schwartz et al., 2005). For both perceptual and attentional load, increasing levels of load usually lead to reduced processing of task-irrelevant information such as distractor stimuli.