“…Task design, data acquisition, and behavioral results of this study have been reported in detail previously 15 , but the fMRI data presented here have not been reported in the previous study. In brief, subjects performed voluntary visual exploration of natural scene images under three different task conditions: searching for a target object, memorizing objects, and free viewing of the same images (Fig.…”
Section: Methodsmentioning
confidence: 91%
“…In all three conditions, a fixation-cross was presented for 2.5 s before and after the scene image presentation. The same fixation-cross was also presented for a random interval of 5.5–8 s between trials.Figure 1Sequence of events in each task condition (modified from 15 ). The time course of each condition is shown in seconds.…”
Section: Methodsmentioning
confidence: 99%
“…Sequence of events in each task condition (modified from 15 ). The time course of each condition is shown in seconds.…”
Section: Methodsmentioning
confidence: 99%
“…The images were photos of plants, flowers, fruits, gardens, boats, rooms, streets, and churches (details are available on request to the authors). The objects naturally blended into the background based on a contrast map for every pair of object and background images 15 (see Supplementary Information for an example of the visual stimulus). A total of 90 stimulus images were generated based on 30 combinations of 15 backgrounds times two sets of five objects; each combination served for three variants of a stimulus image which differed only in the object positions.…”
Section: Methodsmentioning
confidence: 99%
“…During the main task, functional imaging was performed using echo-planar imaging sensitive to BOLD contrast (voxel size: 3 × 3 × 3 mm 3 , 64 × 64 matrix, 36 slices, TR 1950ms, TE 30 ms, flip-angle 76°). MR-compatible EEG and eye tracking systems were also used to record physiological responses, which have been reported elsewhere 15 and were not used in this study.…”
The visual hierarchy of the ventral stream has been widely studied. However, it remains unclear how the hierarchical system organizes its functional coupling during top-down cognitive process. The present fMRI study investigated task-dependent functional connectivity along the ventral stream, while twenty-eight participants performed object recognition tasks that required different types of visual processing: i) searching or ii) memorizing visual objects embedded in natural scene images or iii) free viewing of the same images. Utilizing a seed-based approach that explicitly compared task-specific BOLD time-series, we identified task-dependent functional connectivity of the visual ventral stream, demonstrating different correlation structures. Searching for a target object manifested both correlated and anti-correlated structures, separating the visual areas V1 and V4 from the posterior part of the inferior temporal cortex (PIT). In contrast, the ventral stream structure remained correlated during memorizing objects, but increased the correlation between the right V4 and PIT. On the other hand, V1 and V4 showed task-dependent activation, whereas PIT was deactivated. These results highlight the context-dependent nature of the visual ventral stream and shed light on how the visual hierarchy is selectively organized to bias object recognition toward features of interest.
“…Task design, data acquisition, and behavioral results of this study have been reported in detail previously 15 , but the fMRI data presented here have not been reported in the previous study. In brief, subjects performed voluntary visual exploration of natural scene images under three different task conditions: searching for a target object, memorizing objects, and free viewing of the same images (Fig.…”
Section: Methodsmentioning
confidence: 91%
“…In all three conditions, a fixation-cross was presented for 2.5 s before and after the scene image presentation. The same fixation-cross was also presented for a random interval of 5.5–8 s between trials.Figure 1Sequence of events in each task condition (modified from 15 ). The time course of each condition is shown in seconds.…”
Section: Methodsmentioning
confidence: 99%
“…Sequence of events in each task condition (modified from 15 ). The time course of each condition is shown in seconds.…”
Section: Methodsmentioning
confidence: 99%
“…The images were photos of plants, flowers, fruits, gardens, boats, rooms, streets, and churches (details are available on request to the authors). The objects naturally blended into the background based on a contrast map for every pair of object and background images 15 (see Supplementary Information for an example of the visual stimulus). A total of 90 stimulus images were generated based on 30 combinations of 15 backgrounds times two sets of five objects; each combination served for three variants of a stimulus image which differed only in the object positions.…”
Section: Methodsmentioning
confidence: 99%
“…During the main task, functional imaging was performed using echo-planar imaging sensitive to BOLD contrast (voxel size: 3 × 3 × 3 mm 3 , 64 × 64 matrix, 36 slices, TR 1950ms, TE 30 ms, flip-angle 76°). MR-compatible EEG and eye tracking systems were also used to record physiological responses, which have been reported elsewhere 15 and were not used in this study.…”
The visual hierarchy of the ventral stream has been widely studied. However, it remains unclear how the hierarchical system organizes its functional coupling during top-down cognitive process. The present fMRI study investigated task-dependent functional connectivity along the ventral stream, while twenty-eight participants performed object recognition tasks that required different types of visual processing: i) searching or ii) memorizing visual objects embedded in natural scene images or iii) free viewing of the same images. Utilizing a seed-based approach that explicitly compared task-specific BOLD time-series, we identified task-dependent functional connectivity of the visual ventral stream, demonstrating different correlation structures. Searching for a target object manifested both correlated and anti-correlated structures, separating the visual areas V1 and V4 from the posterior part of the inferior temporal cortex (PIT). In contrast, the ventral stream structure remained correlated during memorizing objects, but increased the correlation between the right V4 and PIT. On the other hand, V1 and V4 showed task-dependent activation, whereas PIT was deactivated. These results highlight the context-dependent nature of the visual ventral stream and shed light on how the visual hierarchy is selectively organized to bias object recognition toward features of interest.
AimThis study aimed to identify atypical hubs in the whole‐brain networks of patients with schizophrenia (SZ) and examine the effects of antipsychotic medications, using electroencephalography (EEG) data.MethodsWe estimated the functional connectivity across all electrodes by applying the phase lag index to the EEG signals of 21 drug‐naïve patients with SZ and 31 age‐matched healthy controls. Betweenness centrality (BC), a measure of hub status, was calculated for each electrode and frequency band. Data from 14 patients were re‐evaluated after initiating treatment with antipsychotic medications.ResultsBC values decreased significantly at the Fz site in the beta band, decreased significantly at Pz in the gamma band, and increased significantly at O1 in the gamma band among patients with SZ. These changes persisted after antipsychotic treatment and were unrelated to clinical symptoms.ConclusionThe abnormal hub topology we observed, especially in the high‐frequency band, may reflect the pathophysiology of SZ, and this study highlights the utility of BC analysis of EEG data for detecting alterations in the whole‐brain networks of patients with SZ.
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