Diagram demonstrating elements of the visual target identification task.

<p>A) A block sequence in the <i>low perceptual load without distractor</i> condition. First, the instruction screen shows “Please Identify” above an elongated nose, for 5 seconds. The elongated nose informs the participants to identify targets in the next task block based on nose shape. During the task block, 16 faces are presented one at a time, for 100 ms each (with 1.1 second inter-stimulus interval). B) A block sequence in the <i>high perceptual load without distractor</i> condition. The instruction screen shows “Please Identify” above two faces without a nose, which informs the participants to identify targets matching the unique combination of face color, and shapes of face, eyes, and mouth in the next task block. C. An example of a face overlaid on a background distractor (i.e., scene picture). The same 64 scene pictures were used in task blocks of both low and high perceptual load. The same instruction screens for low and high perceptual load were used in the distractor and no-distractor conditions.</p

Distractor related changes in BOLD signal at different perceptual load.

<p>Color on T1 template images from SPM2 indicates significant distractor-related increases (red color) or decreases (blue color) in BOLD signal in the conditions of low (A) and high perceptual load (B), and differences in distractor-related changes in BOLD signal at low vs. high perceptual load (C). The color bar indicates t value. The number under each brain image at the bottom row indicates the Z coordinate of the brain image in the MNI (Montreal Neurological Institute) template space. The only voxels displayed on the brain images are those surviving voxel threshold <.01 and cluster level p<.05, FWE corrected for multiple comparisons of voxel-wise whole brain analysis. D) Bar graphs show changes in BOLD signal in the labeled ROIs. The level of BOLD signal at the condition of low load without distractor was defined as baseline (0). Error bars indicates standard errors of means. Abbreviation: H: high load without distractor; HD: high load with distractors; IFG: inferior frontal gyrus; L: low load without distractors; LD: low load with distractors; MOG: middle occipital gyrus; MPFC: medial prefrontal cortex; PAG: periaqueductal gray; R: right; SFG: superior frontal gyrus; VTA/SN: ventral tegmental area and adjacent substantia nigra.</p

Distractor-related changes in BOLD signal.

<p>All clusters in this table were generated at FWE corrected cluster p<.05 with voxel level p<.01. Abbreviations: ACC: anterior cingulate; BA: Brodmann area; G: Gyrus; L: left; MPFC: medial prefrontal cortex; R: right; Size: number of voxels in the cluster; VTA/SN: ventral tegmental area/substantia nigra; Z-value: the Z value of peak voxel in the cluster.</p

Performance data and BOLD signal changes on the task.

<p>A). Error bar indicates standard error of means. Perceptual load showed main effects on commission and omission errors and on RT. Distractors showed significant main effects on commission and omission errors, but only a trend on RT. Perceptual loads and distractors showed a significant two-way interaction with respect to commission errors, and trended towards a significant two-way interaction with respect to omission errors. B) Color on T1 template image from SPM2 indicates significant increases (red color) and decreases (blue color) in BOLD signal in the condition of high relative to low perceptual load, collapsed across distractor conditions. The color bar indicates t value. The number under each brain image indicates the Z coordinate of the image in the MNI (Montreal Neurological Institute) template space. The only voxels displayed on the brain images are those surviving voxel threshold <.01 and cluster level p<.05, FWE corrected for multiple comparisons of voxel-wise whole brain analysis. Abbreviations: L: low load; H: high load; R: right side; RT: reaction time.</p