Fig 1.
(A) Electrode layout used for the experiment. Red ovals indicate the electrodes of interest: TP7, TP8, P7, P8 used in Mima et al. 2001. (B) Illustration of experimental design. (C) Example images of object (top panel) and meaningless object (bottom panel) stimuli.
Fig 2.
Frequency power spectrum averaged over four electrodes of interests (TP7, TP8, P7, P8) for object (2A) and meaningless object (2B) stimuli plotted across time.
Fig 3.
Task-related change in alpha band power averaged over four electrodes of interest (TP7, TP8, P7, P8) and plotted for different time windows.
Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. t1 = 0–500 ms; t2 = 250–750 ms; t3 = 500–1000 ms; t4 = 750–1250 ms. Error bars are SEM. Asterisks indicate p<0.05.
Fig 4.
(A) Task-related change in alpha band coherence averaged for four electrode pairs of interest (TP7-TP8, TP7-P8, P7-TP8 and P7-P8) pairs and plotted for four different time windows. Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. t1 = 0–500 ms; t2 = 250–750 ms; t3 = 500–1000 ms; t4 = 750–1250 ms. Error bars are SEM. (B) Task-related change in imaginary part of coherency for alpha band averaged for four electrode pairs of interest (TP7-TP8, TP7-P8, P7-TP8 and P7-P8) and plotted for four different time windows. Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. t1 = 0–500 ms; t2 = 250–750 ms; t3 = 500–1000 ms; t4 = 750–1250 ms. Error bars are SEM.
Fig 5.
(A) Results of non-parametric cluster-based permutation analysis of power spectrum data for alpha band. Asterisks indicate electrodes that showed significant difference (p<0.05) in alpha power between the two stimulus conditions (Objects minus meaningless objects) that occurred at 0.6s (left) and 0.7s (right). The prominent cluster visible over the left occipito-temporal region included C3, P3, Pz and O1 electrodes. (B) Task-related change in alpha power averaged for the significant electrode cluster (C3, P3, Pz and O1) and plotted for four time windows. Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. t1 = 0–500 ms; t2 = 250–750 ms; t3 = Cxy (f) = 500–1000 ms; t4 = 750–1250 ms. Error bars are SEM. Asterisks indicate p<0.05.
Fig 6.
Results of paired permutation test (objects vs meaningless objects) performed on alpha power spectrum of sources and projected on a template anatomy cortex.
Fig 7.
Regions of interest (ROIs) demarcated based on the results of time-frequency analysis for source space.
The left ROI encompassed the occipito-temporal region in the left hemisphere that showed significant alpha desynchronisation associated with object recognition and the right ROI included the homologous region in the right hemisphere.
Fig 8.
(A) Task-related change in alpha band coherence between the left ROI and right ROI in source space and plotted for four different time windows. Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. t1 = 0–250 ms; t2 = 250–500 ms; t3 = 500–750 ms; t4 = 750–1000 ms. Error bars are SEM. Asterisks indicate p<0.05. (B) Task-related change in imaginary part of coherency for alpha band between the left ROI and right ROI in source space and plotted for four different time windows. Solid black bars represent object stimuli; checked bars represent meaningless object stimuli. T1 = 0–250 ms; t2 = 250–500 ms; t3 = 500–750 ms; t4 = 750–1000 ms. Error bars are SEM. Asterisks indicate p<0.05.
Fig 9.
Results of Granger causality (GC) analysis between left and right ROI in source space for the time window of 250–500 ms.
Solid black bar represents Left to Right GC for object stimuli; solid white bar represents Right to Left GC for object stimuli; solid grey bar represents Left to Right GC for meaningless object stimuli; checked bar represents Right to Left GC for meaningless object stimuli. Error bars are SEM. Asterisks indicate p<0.05.