Fig 1.
Each trial starts with a fixation cross followed by the presentation of a picture which can be of 3 different types, snake face (i), snake shape (ii), or fake snake shape (iii), and presented at 3 different locations in the visual display: centre (A), right (B) or left (C). Following the picture presentation (150 msec), time is given for a response according to the current task. After 3 seconds from stimulus onset, a distraction task starts to ensure maintenance of participants’ attention: counting the number of times number “1” appears and then selecting the right answer in a forced choice display. The inter-stimulus interval (ISI) is of 3 or 6 seconds until a new picture is displayed.
Fig 2.
ROI amygdala: Effect of spatial location.
Responses of the amygdala for centrally presented stimuli are larger than for RVF peripheral presentations, independent of task and amygdala. However, for the contrast ‘centre > LVF’, these differences depend both on task and amygdala: significant differences are found for the left amygdala during the implicit snake identification task (task 1), ROI RFX-GLM contrasts: mean differences in parameter estimates (z-normalized beta-values) for the contrasts ‘centre > RVF’, task 1 (A) and 2 (C), and for the contrasts ‘centre > LVF’, task 1 (B) and 2 (D), are displayed. Legend: LVF, left visual field; RVF, right visual field; amy L, amygdala left; amy R, amygdala right; *p<.05, ** p<.01. The bars display the standard error of the mean (SE).
Fig 3.
ROI amygdala: Effect of stimulus type.
Responses of the amygdala to the snake faces are smaller than to the fake snake stimuli, showing differential decreased activation in a task and amygdala dependent manner. The left amygdala is preferentially involved in the discrimination of threatening and non-threatening stimuli during the threat detection task (task 2). ROI RFX-GLM contrasts: mean differences in parameter estimates (z-normalized beta-values) for the contrasts ‘snake faces > control fake snakes’, task 1 (A) and 2 (B) are displayed. Legend: amy L, amygdala left; amy R, amygdala right; *p<.05. The bars display the standard error of the mean (SE).
Fig 4.
Whole brain: ‘Central vs. Peripheral’ spatial location.
Activated regions yielded by the RFX group analysis for the contrast ‘centre > periphery’. Bilateral amygdala (central panel), pulvinar nucleus of the thalamus (left) and superior colliculus in the midbrain (right) show larger responses to central compared with peripheral presentations. Voxel level threshold was set at p< .05, followed by a cluster threshold correction set at p<.05 which resulted in a minimum cluster size of 170 voxels.
Fig 5.
ROI amygdala: Effect of visual field and stimulus type.
Hemispheric asymmetries are found in a stimulus type dependent manner, as response difference between the centre and each of the visual hemifields (LVF, RVF) are specific for the true snake shapes. ROI RFX-GLM contrasts: mean differences in parameter estimates (z-normalized beta-values) for the contrasts ‘centre > LVF’ and ‘centre > RVF’, for the right and the left amygdala ROI. Legend: LVF, left visual field; RVF, right visual field; *p<.01, corrected for multiple comparisons. The bars display the standard error of the mean (SE).
Fig 6.
ROI amygdala: Effect of visual field and the specificity of the true snake shape stimuli.
Hemispheric asymmetries are found in a stimulus type dependent manner—the right hemisphere (left visual field) responds more to true snake shapes, but the same in not found for the fake snakes (control stimuli). ROI RFX-GLM contrasts: mean differences in parameter estimates (z-normalized beta-values) for the contrasts ‘LVF > RVF’, for the amygdala (left and right ROIs together). Legend: LVF, left visual field; RVF, right visual field; *p<.05, corrected for multiple comparisons. The bars display the standard error of the mean (SE).
Fig 7.
Whole brain: Effect of visual field ‘LVF > RVF’.
Activated regions yielded by the RFX group analysis for the contrast ‘LVF > RVF’. A hemispheric asymmetry was found particularly in the right pulvinar and in the right superior colliculus for LVF presentations of snake stimuli, during the implicit snake identification task, task 1 (n = 20). Legend: LVF, left visual field; RVF, right visual field. Voxel level threshold was set at p<.05, followed by a cluster threshold correction set at p<.05 which resulted in a minimum cluster size of 166 voxels.