Academic journal article Attention, Perception and Psychophysics

Attention to Faces Modulates Early Face Processing during Low but Not High Face Discriminability

Academic journal article Attention, Perception and Psychophysics

Attention to Faces Modulates Early Face Processing during Low but Not High Face Discriminability

Article excerpt

In the present study, we investigated whether attention to faces results in sensory gain modulation. Participants were cued to attend either to faces or to scenes in superimposed face-scene images for which face discriminability was manipulated parametrically. The face-sensitive N170 event-related potential component was used as a measure of early face processing. Attention to faces modulated N170 amplitude, but only when faces were not highly discriminable. Additionally, directing attention to faces modulated later processing (~230-300 msec) for all discriminability levels. These results demonstrate that attention to faces can modulate perceptual processing of faces at multiple stages of processing, including early sensory levels. Critically, the early attentional benefit is present only when the "face signal" (i.e., the perceptual quality of the face) in the environment is suboptimal.

A typical scene contains far more information than the visual system's limited processing capacity can handle at one time. It is under these highly cluttered conditions that our attention system is most necessary for guiding behavior by selecting a behaviorally relevant subset of the available information for further processing. Of the numerous studies that have investigated the neurobiological mechanisms of selection, most have focused on top-down attention to locations in space. These studies suggest that selection results from processing biased in favor of stimuli occurring within relevant versus irrelevant locations of the visual scene (see Mangun, 1995). A key finding of this research is that selection of relevant locations occurs during early visual processing via an increase in the sensory gain of attended relative to unattended channels (Hillyard & Mangun, 1987; Hillyard, Vogel, & Luck, 1998). This increase in sensory gain may result from enhancement of the sensory signal, suppression of task-irrelevant external noise, or a combination of the two (Hopf et al., 2006; Luck et al., 1994). More recent studies have aimed to determine whether attention operates similarly when it is directed to complex objects such as faces (e.g., Downing, Liu, & Kanwisher, 2001).

Faces are a biologically relevant stimulus category with immense social import that may have distinct processing requirements from other stimulus categories (Farah, 1996; Farah, Wilson, Drain, & Tanaka, 1995). Yet functional MRI (fMRI) studies have found a great deal of correspondence between the neural activity patterns seen during both spatial attention tasks and tasks requiring attention to faces. Several studies have established that focusing attention on a location increases activity in visual areas that code for that particular location (Mangun, 1995). Similarly, facesensitive perceptual modules within the occipito-temporal cortex have been reported to demonstrate greater activity when attention is directed to faces versus nonface objects (Lepsien & Nobre, 2007; O'Craven, Downing, & Kanwisher, 1999; Serences, Schwarzbach, Courtney, Golay, & Yantis, 2004; Wojciulik, Kanwisher, & Driver, 1998). Although compelling, these studies are bound by the temporal limitations of fMRI and consequently cannot distinguish between attention-induced modulation of early sensory processing and later modulation due to reentrant signals from attentional control regions.

The millisecond temporal resolution of event-related potential (ERP) and event-related magnetic field (ERMF) methods allows us to better assess the level of processing at which attentional modulations occur. It is well established that early sensory processing, as indexed by the P1 and N1 ERP components, is modulated by spatial attention (Hillyard & Anllo-Vento, 1998). Electrophysiological investigations in nonhuman primates have revealed that attentional effects can occur during feedforward stages of sensoriperceptual analysis during spatial attention tasks (e.g., Luck, Chelazzi, Hillyard, & Desimone, 1997). …

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