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Hilda M. Fehd, Sabine Kastne; Feature-based mechanisms of attention in human visual cortex. Journal of Vision 2004;4(8):619. doi: https://doi.org/10.1167/4.8.619.
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Directing attention to a location in the visual field leads to an increase in activity in visual cortex, even in the absence of visual stimulation (Kastner et al., 1999, Neuron 22: 751). Here we use feature cues to investigate if baseline increases are specific for particular feature dimensions. Three subjects were tested in a 3T head scanner using gradient echo EPI. Color or motion stimuli, chromatic stationary dots or achromatic moving dots, were presented at 12 degrees eccentricity. At the beginning of each presentation block, a feature cue was shown (the letter M or C), and, after a delay, stimuli of the designated feature appeared. Subjects covertly attended to the cued location and counted the occurrences of a target color or direction of motion. In an unattended condition, subjects counted luminance changes of the fixation cross. Areas V1, V2/VP, V4, TEO, and MT were consistently activated in all subjects during visual presentation periods as compared to blank periods. During the unattended presentations all areas responded equally to color and motion stimuli, except for V4 and MT which had a higher response for their preferred stimulus, color or motion, respectively. When subjects expected the stimulus onset, increases of baseline activity were obtained in each visual area and without any differences regarding the cued feature dimension. When subjects attended to the stimuli, visually-evoked activity was enhanced in areas V2/VP, V4, TEO, and MT, as compared to the unattended condition. In V4, the attentional response enhancement on color and motion stimuli was similar. In MT, attentional response enhancement was found on motion, but not on color stimuli. In conclusion, increases in baseline activity appear to be spatially-, but not feature-specific. Baseline increase are not correlated with attentional modulation of visually-evoked activity. Supported by NIMH and Whitehall Foundation.
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