Neural Correlates of Auditory Attention in an Exogenous Orienting Task

In an exogenous orienting task, attention is increased to the target stimulus if the cue validly predicts the target’s location and the cue and target occur in quick succession. With a longer interval between the cue and target, the opposite effect occurs: attention is inhibited for validly cued targets. These attentional phenomena are known as facilitation, and inhibition of return (IOR), respectively. Both effects have been extensively explored in vision but less so in the auditory domain. The visual N2pc, an attention-related eventrelated potential (ERP) component has been used to examine the neural correlates of IOR (McDonald et al., 2009; Yang et al., 2012), but recently, an auditory analog of the N2pc was discovered, known as the N2ac (Gamble & Luck, 2011). To our knowledge, no previous study has explored the neural basis of exogenous attentional facilitation and IOR in the auditory modality. The present study sought to fill this gap using the N2ac as a neural marker of auditory spatial attention. Brain activity was recorded from nineteen participants while they performed a Posner exogenous auditory orienting task. We compared the ERPs elicited by the target stimulus for short (200 ms) cue-to-target intervals (facilitation), and long (700 ms) cue-to-target intervals (IOR). We observed behavioral and electrophysiological evidence of attentional facilitation, and a behavioral trend of IOR, but no apparent electrophysiological evidence of IOR. This study demonstrates that the N2ac is enhanced by exogenous attention during the facilitation phase of the cue-to-target interval, but remains unaffected during the later IOR phase. These findings suggest some similarities as well as some differences between this newly discovered ERP component (N2ac) and its visual analog, the N2pc. To my mom and dad, and to all the infinite cosmic luck that brought me to you Chapter 1: Introduction 1.1 Auditory orienting and spatial attention Relevant sensory signals exist always in the presence of concurrent irrelevant signals. For humans and most organisms, processing complex incoming sensory information and orienting attention to different locations in the environment is fundamental to successful adaptive behavior. Spatial attention can be oriented by intentionally allocating attention to a specific location, known as endogenous orienting. Conversely, attentional orienting can occur automatically and reflexively, known as exogenous orienting, based on the salience of a stimulus (Mondor & Breau 1999). A good way to illustrate the different types of attentional orienting is with relatable examples. If you were walking through a dark forest and heard a noise coming from behind a tree, your attention would automatically focus on the location of that noise. This response occurs instinctively, and you don’t need to actively make the decision to pay attention to the noise you hear. Because of your current location (the dark forest), it is very advantageous that you respond quickly and reflexively. This is an example of exogenous orienting, and the noise is an example of an exogenous cue. While the noise heard in a dark forest is a particularly salient stimulus, exogenous orienting of attention occurs from many different types of cues in the external environment, such as the brightening of a light or the sound of a door slamming. However, our attention is also controlled volitionally, when we take the time to interpret a sound cue and then internally generate a decision for how we want to respond. This type of attention, brought under the control of our goals and decisions, is called endogenous orienting. The most frequently used example of an endogenous cue is an arrow pointing towards a specific direction. Unlike the noise in the dark forest, an arrow doesn’t cause an instinctive response, but instead requires you to make a decision about how you will direct your attention. Similarly, attentional orienting in the auditory sensory modality occurs both, reflexively and in a goal-oriented fashion, that is, under the control of exogenous cues from the external environment, and endogenous cues from the internal environment.