Chapter 6 Summary

Attention is a vital cognitive function that plays a fundamental role in virtually everything we do. It was initially studied by cognitive psychologists using behavioral measures such as reaction time, discrimination accuracy, and the ability to report the content of attended versus unattended stimulus streams. This early work established that attention is limited in its capacity, confirming the intuition that it is difficult to attend to more than one thing at a time, and that when people are asked to do so, their performance deteriorates.
A major distinction in attention research has been between the ways that processing resources are induced to be directed toward locations or stimuli in the environment. Endogenous attention is the ability to voluntarily direct attention according to one’s goals, expectations, or knowledge. Exogenous (or reflexive) attention consists of attention triggered by particularly salient stimuli in the environment. Both lead to enhanced processing of the location and/or stimuli toward which attention has been directed.
The ability to ascertain how, when, and where attention operates in the central nervous system is limited using behavioral measures alone. Understanding of both the psychological and the neural mechanisms of attention has been greatly advanced by combining behavioral approaches with cognitive neuroscience methods, including the direct recording of brain activity while humans or other animals are engaged in attentional tasks.
Electrophysiological studies in both humans and experimental animals have shown that the effects of auditory and visual spatial attention on stimulus processing can begin at the early cortical processing stages in the ascending sensory pathways—in humans as early as 20 milliseconds in audition and 70 milliseconds in vision, consistent with early selection theories of information processing. Corresponding neuro-imaging studies have shown that spatial attention specifically enhances stimulus processing activity in the sensory cortical areas that process the attended region of space.
Attention can also be directed toward nonspatial attributes of stimuli, such as their feature attributes (e.g., pitch or color) or object characteristics. Such nonspatial attention tends to influence stimulus processing activity somewhat later in time than does spatial attention. Like spatial attention, feature and object attention enhances stimulus-evoked activity in the sensory cortical regions specifically involved in the processing of that particular stimulus attribute.
Under some circumstances, such as during the attentional blink, attention influences stimulus processing only at later stages, involving higher levels of analysis in non-sensory cortical regions. More generally, attention effects can also occur at later phases of processing in a reentrant way, influencing stimulus-evoked activity in low-level sensory cortical regions, but at later stages of processing.
Single-unit studies in experimental animals have provided insight into the details of attentional effects on stimulus processing at the cellular level. Neurons fire at higher rates when the location of the stimulus in space is attended and/or the when stimulus attributes to which they are tuned are attended. Attention to a stimulus feature in one location tends to enhance the processing of that feature for all stimuli in the visual field.
Recent studies have increasingly focused on how attention operates in multisensory contexts, rather than just within a single sensory modality. A particularly key finding is that attention is important for facilitating the integration of stimulus information from several modalities into a multisensory perceptual whole.