Electrophysiological Correlates of Covert Attention Guidance in Natural Scenes

[摘要] When observers attend a lateralized target item that is presented simultaneously with distracting visual information, a lateralized component is observed in the event-related brain potential (ERP) at about 200-300ms after stimulus onset, the so-called N2pc. While this component has been extensively studied with simple stimuli like bars and textures, the N2pc has rarely been tested for natural scenes. We presented grayscale natural scenes and noise patterns that were matched with respect to their amplitude spectrum. In some conditions ("split display"), one hemifield contained noise, the other the natural scene; in other conditions ("complete display"), either the noise or the natural scene spanned the whole display. Gabor wavelets (width (sd) of envelope: 0.6 degrees, spatial frequency: 1.9 cyc/deg ) that were either tilted 30° to the left or right served as targets. In each trial, a target appeared at one of 6 distinct locations on the scene in 5.8 degrees distance from fixation. Two of the potential target locations were in each hemifield, two on the vertical midline. In each trial, target item and background were presented simultaneously, and observers had to report the orientation of the Gabor while maintaining central fixation. We found differences between the signals at electrodes contra- and ipsilateral to the target in a time window around 200ms to 280ms after stimulus onset, which correspond to the N2pc observed for simple stimuli. For both display conditions, differences in N2pc morphology were observed between targets embedded in the natural scene and targets embedded in the noise. Control analyses based on the vertical-midline targets demonstrated that these effects cannot be attributed to physical differences between natural scenes and noise. We suggest that natural scenes play a similar role as singleton distractors in simple displays, namely to capture attention that is beyond volitional control.

[学科分类] 眼科学