Academic journal article Canadian Journal of Experimental Psychology

Load Theory Behind the Wheel; Perceptual and Cognitive Load Effects

Academic journal article Canadian Journal of Experimental Psychology

Load Theory Behind the Wheel; Perceptual and Cognitive Load Effects

Article excerpt

Driving is an everyday task where attention is crucial and lapses can have fatal consequences. Road traffic accidents remain a significant public health concern globally; an estimated 1.3 million people die in road traffic accidents every year, and an estimated 20-50 million are injured (United Nations Road Safety Collaboration, 2010). Although it can be difficult to identify the exact cause of an accident, it is estimated that almost half of all crashes in the US involve driver inattention (Stutts, Reinfurt, Staplin, & Rodgman, 2001). Driving, more than almost any other daily task, stands to benefit from advances in attention research. Although drivers' divided attention has been the focus of much research, for example, studies on the impact of mobile phone use, in-vehicle information systems, and passenger conversations (Birrell & Fowkes, 2014; Drews, Pasupathi, & Strayer, 2004; Strayer & Drew, 2004), more basic questions regarding drivers' selective attention remain unanswered. Given the many objects visible across an average road scene, how do drivers focus on what is relevant and ignore what is irrelevant?

Attention research has long been divided between those who propose that selective attention happens at an early stage and those who argue that selective attention is a late stage process. If applied to driving, the "early selectionist" view would suggest that because perceptual capacity is limited, drivers process only what is taskrelevant (vehicles, pedestrians, and road signs that need to be noted for safe driving) and do not process irrelevant information (such as billboards and shop fronts; Sperling, 1960; Treisman, 1969). The "late selectionists" hypothesise that perceptual capacity is unlimited, therefore all stimuli are initially processed, before selective attention mechanisms focus on that which is relevant at a later stage ( Deutsch & Deutsch, 1963; Norman, 1968). In a driving task, this would suggest that all available stimuli (including taskirrelevant billboards) are initially processed, before selective attention intervenes to prevent such irrelevant stimuli affecting behaviour.

After many decades of debate and conflicting evidence, Nilli Lavie proposed a hybrid theory of attention in which both early and late selection are possible (Lavie, 1995, 2005; Lavie, Hirst, de Fockert, & Viding, 2004; Lavie & Tsal, 1994). Load Theory suggests that perceptual capacity is limited, but that this capacity is always involuntarily filled. The extent to which a task consumes available perceptual capacity is termed perceptual load. Perceptual load can be described as "the amount of information involved in the processing of the task stimuli" (Macdonald & Lavie, 2011, p. 1780). When a task imposes high perceptual load, perceptual capacity is exhausted and no additional, task-irrelevant stimuli are processed-early selective attention is inevitable. However when a task imposes low perceptual load, there are additional perceptual resources that "spill-over," continuing to process any additional stimuli. This necessitates late selection, involving top-down control of attentional priorities. The success of selective attention at this later stage is contingent on the cognitive load imposed by the task. Cognitive load is the demand placed on executive cognitive control functions, such as working memory. High cognitive load (typically manipulated by loading working memory with a string of letters or numbers) has the opposite effect of perceptual load, increasing distractor interference as the cognitive resources needed to suppress the distractors are employed elsewhere (Lavie & DeFockert, 2005). Perceptual and cognitive load can be difficult to disentangle and given that they are purported to have opposite effects, this is a crucial element of the design of any Load Theory study. There are other valid criticisms of the load hypothesis (see Benoni & Tsal, 2013; Khetrapal, 2010 for reviews), and some studies have produced findings that are not in line with the load hypothesis, often when altering the classic load paradigm (e. …

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