Selective attention

A basic characteristic of human perception is its selectiveness. Because our information processing capacity is limited (e.g., Broadbent, 1958; Neisser, 1967), we attend to some stimuli in our environment while ignoring others. As a result, we perceive the former while the latter gets lost. An issue that has kept researchers busy for decades concerns the fate of unattended stimuli: To what extent are they processed? Do we register only their elementary perceptual features such as their location, color, or shape, or do we also compute their meaning? The first part of this chapter is devoted to examining the current status of what has become known as the early versus late selection debate. Another important question concerns the factors that determine which stimuli are selected at a given time. A core premise of most leading models of visual search is that selection is guided by both stimulus-driven and goal-directed factors (e.g., Bundesen, 2005; Treisman & Sato, 1990; Wolfe, 2007). For instance, according to the biased competition model (e.g, Desimone & Duncan, 1995), object representations compete for neural representation in our brains. Items that are highly salient enjoy a competitive advantage relative to low-salience items, but the goals of the observer bias this competitive process, thereby ensuring that low-salience objects that are highly relevant to the task at hand are also represented across the visual hierarchy. However, claims that attention selection might be guided exclusively by how salient an object is, irrespective of the observers' intentions or, alternatively, only by the goals adopted by the observers, have ignited a heated debate that has generated considerable research in the past 20 years and are reviewed in the second section of this chapter. For goal-driven processing of relevant information to be at all possible, representations of certain object characteristics, which meet the observer's goal, must be activated within long-term memory and maintained during the task. This formulation of goal-directed attention highlights the close relationship between attention and working memory (e.g., Awh, Vogel, & Oh, 2006; Cowan, 1995). In the third section of this chapter, we provide a selective review of the growing behavioral literature demonstrating interactions between memory of spatial locations, features, and objects and the deployment of attention and of neuroscientific findings showing that the neural structures associated with working memory and attention often overlap (see also Naime & Neath, this volume). The last issue covered by this chapter focuses on the relationship between attention and conscious awareness (see also Banks & Farber, this volume). Although cognitive psychologists have long been interested in the unconscious mind, and in particular in establishing how deeply information that is not consciously perceived can be processed (e.g., see Kouider & Dehaene, 2007 for a recent review), more recent research has shifted toward the study of conscious awareness. In particular, since Crick and Koch (1990) launched the search of the neural correlates of consciousness, a large number of studies have contrasted conscious and unconscious processing in order to elucidate what specific mechanisms characterize conscious perception. Within this framework, they have often used attentional manipulations in order to exclude parts of the visual field from conscious awareness, implying that there might be a causal relationship between attention and awareness. Here, we review the findings pertaining to the question of whether attention to an object is necessary and sufficient for conscious perception of this object to arise.