Attention Improves Encoding of Task-Relevant Features in the Human Visual Cortex

Abstract

When spatial attention is directed towards a particular stimulus, increased activity is commonly observed in corresponding locations of the visual cortex. Does this attentional increase in activity indicate improved processing of all features contained within the attended stimulus, or might spatial attention selectively enhance the features relevant to the observer’s task? We used fMRI decoding methods to measure the strength of orientation-selective activity patterns in the human visual cortex while subjects performed either an orientation or contrast discrimination task, involving one of two laterally presented gratings. Greater overall BOLD activation with spatial attention was observed in areas V1-V4 for both tasks. However, multivariate pattern analysis revealed that orientation-selective responses were enhanced by attention only when orientation was the task-relevant feature, and not when the grating’s contrast had to be attended. In a second experiment, observers discriminated the orientation or color of a specific lateral grating. Here, orientation-selective responses were enhanced in both tasks but color-selective responses were enhanced only when color was task-relevant. In both experiments, task-specific enhancement of feature-selective activity was not confined to the attended stimulus location, but instead spread to other locations in the visual field, suggesting the concurrent involvement of a global feature-based attentional mechanism. These results suggest that attention can be remarkably selective in its ability to enhance particular task-relevant features, and further reveal that increases in overall BOLD amplitude are not necessarily accompanied by improved processing of stimulus information.

Feature-Selective Attentional Modulations in Human Frontoparietal Cortex

“…However, we found stronger representations of orientation during attend-orientation scans relative to attend-luminance scans in multiple posterior sensory and frontoparietal cortical areas. This finding dovetails with other reports suggesting that featurebased attention can selectively enhance representations of task-relevant features without enhancing representations of taskrelevant features that are part of the same object (Serences et al, 2009;Xu, 2010;Jehee et al, 2011), and demonstrates that featurebased attentional modulations are distributed across the visual processing hierarchy, including regions typically associated with attentional control rather than sensory processing. Traditionally, "sources" and "targets" of attentional control signals have been distinguished on the basis of univariate response properties (e.g., averaged single-unit/population spike rates or averaged fMRI activation).…”

“…Invasive electrophysiological recordings in nonhuman primates (McAdams and Maunsell, 1999;Treue and Martinez-Trujillo, 1999;Martinez-Trujillo and Treue, 2004) and functional neuroimaging studies in humans (Serences and Boynton, 2007;Jehee et al, 2011) suggest that FBA enhances cortical representations of behaviorally relevant visual features in early visual areas. These enhancements are thought to result from top-down feedback signals originating in frontoparietal cortical areas (Serences et al, 2004;Kelley et al, 2008;Greenberg et al, 2010;Zhou and Desimone, 2011;Baldauf and Desimone, 2014;Gregoriou et al, 2014).…”

Action Preparation Shapes Processing in Early Visual Cortex

“…This modulation may be instantiated by a shift in orientation tuning for neurons in the orientation columns (Kamitani and Tong, 2005;Norman et al, 2006;Jehee et al, 2011), or on a larger cortical scale by changes in radial bias of orientation representation (Sasaki et al, 2006;. Both explanations, however, imply neural changes in the orientation representation in early visual cortex due to action preparation.…”

Separable Mechanisms Underlying Global Feature-Based Attention

“…Moreover, it demonstrated that FBA operates in a spatially global way, that is, outside the spatial focus of attention (Maunsell and Treue, 2006). Signatures of global FBA were also documented at the neural population level with fMRI and electromagnetic recordings [electroencephalogram (EEG)/magnetoencephalogram (MEG)] in humans (Saenz et al, 2002;Hopf et al, 2004;Zhang and Luck, 2009;Boehler et al, 2011a;Jehee et al, 2011). For example, Saenz et al (2002) showed that attention to color or motion direction in one visual hemifield increased the BOLD response in striate and extrastriate cortex contralateral to a matching color or motion direction in the unattended visual hemifield.…”