Article Figures & Data
Figures
- Figure 1.
The encoding locations of the four Gabor stimuli in primary visual cortex for each of the four subjects were retinotopically localized in primary visual cortex by using a flickering dartboard presented alternatively at each of the same four positions in which the Gabor stimuli were later presented to investigate saccadic suppression. Each stimulus position (color coded) revealed its corresponding encoding cluster in V1 (see Materials and Methods, Retinotopic localization of the stimuli in V1). Statistical analysis of BOLD signals in the main experiment was restricted to time series extracted from these clusters (labels indicate the MNI coordinate of the corresponding coronal, axial, and sagittal sections).
- Figure 2.
Schematic illustration of the time course of an actual trial from the G+S condition in which Gabor stimuli were flashed immediately before the saccadic onset. At the start of each trial, the participants fixed their gaze on a centrally located fixation dot. In a step procedure, the central fixation dot was extinguished and the saccadic target appeared on the periphery, eliciting the preparation of a saccade. Immediately before saccadic onset, four Gabor stimuli were simultaneously flashed. The bottom represents an actual eye-movement trace. Time marks designate triggers to the scanner acquisition onsets (red) and stimulus onset triggers coming from the visual stimulus generator (green), to which fixed image-formation delays were applied (see Materials and Methods, Eye movement recording and stimulus presentation).
- Figure 3.
Behavioral cumulated data from all participants collected during the MR measurements. In the bottom, the histogram shows the percentage of the total number of G+S trials (n = 2020) sorted according to their measured SOA, showing how, as a result of the adaptive algorithm used, in the majority of trials the Gabors were flashed during the premotoric time window before saccadic onset. Only trials with SOAs between −100 and 0 were included in the analysis (gray bars and shaded area), whereas the rest (white bars) were discarded. The squares show performance in the orientation discrimination task. Percentage of trials in which subjects did not detect the presence of the Gabor stimuli is shown by the circles and indicates that, on ∼25% of the trials, the Gabors were not perceived, although they were presented on a stationary retina, a sort of saccadic blindness.
- Figure 4.
Average peak responses from G+S trials as a function of SOA. The amplitude of an otherwise constant hemodynamic response function was modulated by a second-order polynomial function to improve the fit to the data by accounting for the effect of SOA (see Materials and Methods, Data analysis). Each graph shows the average peak responses plotted against SOA across all 12 sessions for each of the four subjects. Error bars represent ±1 SD.
Additional Files
Supplemental data
Files in this Data Supplement:
- supplemental material - SD. 1 Can V1 responses 8ms Gabor stimuli be measured with fMRI? After retinotopically localizing the Gabors, three fMRI sessions were conducted to confirm the detectability of such short-lived responses in V1 (blue). During these sessions, Gabors were repeatedly presented for 8 ms every 9 s (plus a random jitter) while maintaining fixation. In this event related peristimulus-time histogram (obtained from averaging time-series extracted from the four regions of interest) we can appreciate how BOLD signal significantly increases when the Gabors were presented (p < 0.000001).
- supplemental material - SD. 2 Psychometric function for the orientation discrimination task were obtained for each subject by using a standard constant stimulus procedure with rotation values of 1, 2, 3, 6, 12, 24 and 48 degrees. Rotation values yielding correct responses in 80% of the trials were used in the main experiment to avoid floor and ceiling effects.
- supplemental material - SD. 3 Presentation delays. To account for presentation delays, we recorded the digital page-change triggers coming from the stimulus generator (red) together with the actual Projector�s luminance output (green) measured on the screen. Image formation started systematically one frame after actual analog-signal output of the VSG. Discounting rise and decay times (FWHM), we estimated an effective onset stimulus duration of 8 ms (blue). These values were used to precisely calculate SOAs and make sure stimuli included in the analysis were presented before the onset of the saccade.
- supplemental material - SD. 4 Saccadic onset detection. Saccadic onset detection accuracy was visually inspected by plotting the eye traces from the detected onset to make sure that in all analyzed trials, the Gabor stimuli where presented presaccadically. On this plot, the detection accuracy for one session is presented.
- supplemental material - SD. 5 BOLD response magnitude for the ROI as a function of peristimulus time, where zero corresponds to the event onset. The curves depict fitted HRFs to BOLD measurements from the Gabors-only condition (G, circles), the saccade-only condition (S, squares) and the Gabor-plus-saccade condition (G+S, triangles, discarded trials from one session). The amplitude of responses in the G+S condition roughly corresponds to the summation of the effects from the S and the G control conditions. Each data point depicts the average BOLD response for all voxels within the ROI
