RAPID COMMUNICATION Graded Effects of Spatial and Featural Attention on Human Area MT and Associated Motion Processing Areas

Graded effects of spatial and featural attention on human area MT subjects ’ visual attention differently. and associated motion processing areas. J. Neurophysiol. 78: 516– 520, 1997. Functional magnetic resonance imaging was used to quantify the effects of changes in spatial and featural attention on M E T H O D S brain activity in the middle temporal visual area and associated motion processing regions (hMT/) of normal human subjects. FMRI was used to record changes in blood oxygenation and When subjects performed a discrimination task that directed their flow evoked by brain activity in human subjects (n 8) engaged spatial attention to a peripherally presented annulus and their fea- in a visual discrimination task (for details see DeYoe et al. 1996). tural attention to the speed of points in the annulus, activity in During each magnetic resonance (MR) scan series, 102 echoplanar hMT / was maximal. If subjects were instead asked to discriminate brain volumes were collected (repetition time 2 s, in-plane reso-the color of points in the annulus, the magnitude and volume of lution 3.75 1 3.75 mm, 10 axial slices 8 mm in thickness activation in hMT / fell to 64 and 35%, respectively, of the pre- spanning visual cortex; up to 3 repetitions of each condition aver-viously observed maximum response. In another experiment, sub- aged to increase signal-to-noise ratio). Active brain regions werejects were asked to direct their spatial attention away from the determined by cross-correlating each voxel’s MR time series with annulus toward the fixation point to detect a subtle change in reference waveforms representing the neuronal-hemodynamic re-luminance. The response magnitude and volume dropped to 40 and sponse to the stimulus. Response magnitude was calculated as th