Article Figures & Data
Figures
- Figure 1.
Temporal integration masking: stimuli, trial sequence, and expected MEG effects. Illustration of a typical sequence of visual stimuli within one trial (here shown for the case of 200 ms of SOA between mask and target display). With the offset of a fixation dot commenced a temporally jittered pre-mask period (800–1300 ms). Then a random line pattern was presented and remained on the screen when the target display (two diagonally crossing lines (X) with varied set size) was presented. The SOAs between mask and target onset used in this experiment were 0, 33, 50, and 200 ms. The targets superimposed upon the masking pattern (here shown 60% transparent for illustrative reasons) were always shown for 50 ms. Whereas we expect ongoing or cognitively induced oscillatory activity in the pre-mask interval, the onset of the masking pattern is expected to evoke a visual response ∼100 ms after mask onset (estimated from the data, although caution has to be taken as to the exact absolute latency of the evoked response; Vanrullen, 2011). Consequently, the expected latency of the target-evoked response given an affine transformation of physical time to neural time can be estimated by adding the specific SOA to these 100 ms. The objections to the absolute latency do not apply to this relational metric.
- Figure 2.
Higher pre-mask β-power within incorrect compared with correct trials. A, Time-frequency plot showing the percentage in signal change in oscillatory power within correct compared with incorrect trials ((correct-incorrect)/incorrect) around mask onset within an occipital cluster of sensors shown in B and C. Warm colors indicate higher power in correct trials, cold colors in incorrect trials. There are two obvious effects within lower β-frequencies (15–20 Hz) at −350 and −50 ms. B, Head topography showing the percentage in signal change in oscillatory power at 15 Hz like in A averaged over the 500 ms pre-mask interval. C, Corresponding head topography on mean power differences at 15 Hz in the 500 ms pre-mask interval between correct (cor) and incorrect (incor) trials (t values); nonsignificant t values as derived from cluster permutation statistics are masked. Both topographies in B and C show a cluster of parieto-occipital sensors. D, DICS-beamformer source localization of the mean differences in oscillatory power (t values) at 15 Hz averaged over the 500 ms pre-mask interval. T values below an α-level of 0.05 are masked. One oscillatory source is located at the right occipital pole, a second one within left inferior temporal areas. E, Waveforms showing mean power at 15 Hz across subjects (solid line) within the cluster of sensors depicted in C over the 500 ms pre-mask interval for correct (red) and incorrect trials (blue). Shaded areas show the SEM for within-subject designs (similar to the description in Cousineau, 2005). Individual prestimulus power measures across time of each subject have been centered on their average prestimulus power across time points and conditions before calculating the SE.
- Figure 3.
Pre-mask-power effect occurs mostly in long SOA trials. A–C, Waveforms showing mean power at 15 Hz across subjects (solid line) within the cluster of sensors depicted in Figure 2C, over the 500 ms pre-mask interval for correct (red) and incorrect trials (blue) and mask-only trials (green) with a mask-target SOA of 33 (A), 50 (B), and 200 ms (C). Shaded areas show the SEM for within-subject designs (similar to the description in Cousineau, 2005). Individual prestimulus power measures across time of each subject have been centered on their average prestimulus power across time points and conditions before calculating the SE. Even though β-power is stronger for incorrect trials for all SOAs, this effect is only significant for the long SOA trials (200 ms) on the cluster level and reaches its peak difference around −50 ms before mask onset. D, Mean power over the occipital cluster of sensors depicted in Figure 2C at 15 Hz and −50 ms before mask onset for correct (red), incorrect (blue), and mask-only trials (green) across SOAs. Error bars indicate 1 SEM for within-subject designs (similar to the description in Cousineau, 2005). Individual prestimulus power measures of each subject have been centered on their average prestimulus power across conditions before calculating the SE. The difference between correct and incorrect trials is strongest for the long SOA trials (200 ms). Both power decreases for correct trials and increases for incorrect trials with longer SOA.
- Figure 4.
Stronger mask-evoked response within correct compared with incorrect trials. A, Mask-evoked response on a representative central parietal sensor (as shown in B and C). The gray-shaded area around the peak response (approximately +100 ms) denotes the interval within which the visual-evoked field differs significantly between correct (red) and incorrect trials (blue) on the cluster level. B, Head topography showing the difference in amplitude between correct (cor) and incorrect (incor) trials averaged over the interval from +60 to +130 ms after mask onset. Warm colors indicate higher amplitude in correct trials, cold colors in incorrect trials. C, Corresponding head topography on mean amplitude differences averaged over the interval from +60 to +130 ms after mask onset between correct and incorrect trials (t values); nonsignificant t values as derived from cluster permutation statistics are masked. Both topographies in B and C show a cluster of central parietal sensors and include the representative sensor (white, black dot) from A. D, LCMV-beamformer source localization of the mean differences in amplitude (t values) averaged over the interval from +50 to +200 ms post-mask interval. T values below an α-level of 0.05 are masked. Mostly left hemispheric, widespread parietal activity differences account for the effect on the source level (peak difference in left inferior parietal areas). E, Time-frequency plot showing the percentage in signal change in ITC within correct compared with incorrect trials ((correct-incorrect)/incorrect) around mask onset averaged over occipital and parietal sites (white dots shown in top inset). Data points with nonsignificant differences in ITC (as derived from cluster permutation statistics) and significant differences in power (on single sensor level) are masked. Warm colors indicate higher ITC in correct trials, cold colors in incorrect trials. The major effect is centered approximately +100 ms after mask onset within evoked alpha activity. The head topography of the percentage signal change in ITC averaged over the interval from +60 to +130 ms after mask onset and 7–12 Hz is shown in the top inset.
- Figure 5.
Differential-evoked response profiles for short and long SOA trials. A, Mask-evoked response on a representative central parietal sensor (as shown in Fig. 4B,C) for trials with a mask-target SOA of 33 (A), 50 (B), and 200 ms (C). The gray-shaded area around the peak response (approximately +100 ms) denotes the interval within which the visual-evoked response differs significantly between correct (blue) and incorrect trials (red) on the cluster level. Even though the evoked response is stronger in correct trials for all SOAs, this effect is only significant for the short SOA trials (33 and 50 ms) on the cluster level. The orange-shaded area highlights a target-related response over an interval during which both correct and incorrect trials differ significantly on the cluster level from mask-only activity. The exact latency of this effect varies with SOA: for 33 ms SOA from +230 to +300 ms, but not very visible on this particular sensor; for 50 ms SOA from +260 to +330; for 200 ms SOA from +320 to +460 ms. For better comparability of SOA-related latency differences also target display onset is indicated with an orange dotted line for each SOA. D, Mean amplitude at the representative central parietal sensor (shown in Fig. 4B,C) at +115 ms after mask onset for correct (red), incorrect (blue), and mask-only trials (green) across SOAs. Error bars indicate 1 SEM for within-subject designs (similar to the description in Cousineau, 2005). Individual evoked amplitude measures of each subject have been centered on their average evoked amplitude across conditions before calculating the SE. The difference between correct and incorrect trials is strongest for the short SOA trials (33 and 50 ms). Whereas amplitude in correct trials is relatively stable across SOAs, it is the visual-evoked response in incorrect trials–in particular with short SOAs (33 and 50 ms)–that is reduced.
- Figure 6.
Interaction between pre-mask oscillatory power and visual-evoked response across SOA. Difference in effect size between correct and incorrect trials (Δ z-score) for pre-mask oscillatory power and visual-evoked activity for the three levels of SOA (33, 50, and 200 ms). The z-standardized difference in oscillatory power (blue) between correct and incorrect trials within the occipital cluster of sensors depicted in Figure 2C at 15 Hz and −50 ms before mask onset (as shown in Fig. 3D) is largest for long SOA trials (200 ms). In contrast, the z-standardized difference in amplitude (red) between correct and incorrect trials at the representative central parietal sensor (shown in Fig. 4B,C) at +115 ms after mask onset (as shown in Fig. 5D) is largest for short SOA trials (33 and 50 ms). Error bars indicate 1 SEM for within-subject designs (similar to the description in Cousineau, 2005). Individual effect sizes of each subject have been centered on their average effect size across conditions before calculating the SE.
Tables
SOA (ms) Set size % Correct trials SD (%) 0 Mean (all) 2.8 2.8 33* Mean (all)* 66.5* 10.5* 1 item 77.1 11.6 2 items 64.9 14.0 3 items 57.5 11.0 50* Mean (all)* 77.3* 9.8* 1 item 86.6 8.2 2 items 76.3 11.9 3 items 69.1 11.2 200* Mean (all)* 85.0* 7.5* 1 item 92.7 5.4 2 items 89.7 8.0 3 items 85.4 8.7 4 items 72.1 14.8 Mean (all) 0 item (mask only control) 91.0 6.8 Enumeration performance (mean and SD of proportion of correct trials in %) across subjects (N = 14). The first row shows below chance performance (20%) for common onset masking (0 ms SOA) and hence total temporal integration of mask and target information across all set sizes.
↵*Then the percentage of correct trials across the different levels of SOA and for each set size is displayed. The last row depicts performance in the mask-only (0 items) control condition across all SOAs.
