Figure 1.
Sequence of events during a representative trial of Experiment 1 (left) and Experiment 2 (right).
In both experiments, participants were requested to fixate at a central cross for a randomly variable period of time between 1000 to 1500 ms. In Experiment 1, the fixation cross became slightly bigger for 66 ms and was followed by an active or a sham single TMS pulse delivered on the right FEF, 80,100 or 140 ms prior to target onset. In Experiment 2, a peripheral visuo-spatial cue, consisting in a black circle was displayed for 66 ms to the right or the left of the fixation cross. The cue was predictive about the location of the subsequent target (75% valid and 25% invalid trials), and was followed by a TMS pulse delivered 80 ms pre-target onset. In both experiments active or sham TMS pulses were interleaved in a randomized order. Then, after an interstimulus interval (ISI) of 233 ms, a Gabor with the lines tilted to the left or the right appeared for 33 ms at the center of one of the two lateral boxes. Participants were then requested to perform two sequential tasks; first a visual line categorization task to indicate the orientation of the Gabor lines (left/right) and second, a conscious visual detection task in which they had to report if they did see the target, and where they saw it (left/right). A cue is considered valid when it correctly signals the location of the upcoming target (left or right), and invalid when it incorrectly signals target location. A valid trial is the one including a valid cue and the opposite applies to invalid trials. The figure shows for Experiment 2 an example of a valid trial (see Material and Methods for full details on the behavioral paradigms).
Figure 2.
TMS targeted region, neuronavigation and coil placement.
The specific location of the right FEF was identified and labeled in a three dimensional reconstruction of each participant’s MRI. The area was targeted with a 70 mm figure-of-eight TMS coil guided by a frameless stereotaxic neuronavigation system (a and b). The active TMS coil was placed flat with its center tangential to the targeted site and oriented lateral to medial and rostral to caudal orientation (c), approximately parallel to the medial portion of the central sulcus, i.e., ∼ a 45° angle with respect to the interhemispheric fissure. See axial (d), coronal (e) and sagittal (d) MRI views of the location for the TMS targeted right FEF (see Material and Methods for full details on the targeting strategy).
Figure 3.
TMS-induced modulations of right FEF pre-target activity on conscious detection (Experiment 1).
Perceptual sensitivity (mean ± SE) for the three different timings (80, 100 and 140 ms pre-target onset) used in Experiment 1. Data is presented separately for targets displayed in the visual field contralateral (left visual field, LVF) or ipsilateral (right visual field, RVF) with respect to the targeted right FEF under active (red) or sham (blue) TMS stimulation. A main effect of TMS condition was observed, with higher perceptual sensitivity scores under active than sham TMS pulses (F(1,9) = 8.31, p = 0.018). Based on the a priori hypothesis that such effect depended on timing, we performed three separate repeated measures ANOVA for the three timings. The TMS effect only reached significance when pulses were delivered 80 ms pre-target onset (F(1, 9) = 9.77, p = 0.012), but not when applied 100 ms (F = 5.09, p = 0.051) nor 140 ms (F = 3.95, p = 0.078) pre-target onset.
Table 1.
Data from TMS-induced modulations of right FEF pre-target activity on visual performance (Experiment 1).
Figure 4.
TMS-induced modulations of FEF pre-target activity on conscious detection after cue-driven attentional orienting (Experiment 2).
Perceptual sensitivity (mean ± SE) for targets displayed in the visual field contralateral (left visual field, LVF) or ipsilateral (right visual field, RVF) with respect to the stimulated right FEF site under active TMS (red) or sham TMS (blue). An interaction between validity and TMS proved statistically significant (F(1, 6) = 6.54, p = 0.043) indicating that, when delivered after the presentation of a peripheral predictive visuo-spatial cue, TMS pulses yielded significant bilateral enhancements of conscious visual detection only when the cue correctly signaled the location of the subsequent target (valid trials, F = 19.26, p = 0.005, indicated by the asterisk), whereas no effects were observed when the cue incorrectly predicted it (invalid trials, F<1).
Table 2.
Data from TMS-induced modulations of FEF pre-target activity on visual performance after cue-driven attentional orienting (Experiment 2).