Article Figures & Data
Figures
- Figure 1.
Different mechanisms of target and mask frequency interactions. A, Averaged ECoG data from monkey 1 when a single counterphase grating presented at 25% contrast and varying temporal frequency was used to obtain the SSVEP response function. Curves indicate a polynomial fit (degree = 3). Cyan and magenta dots represent the two target frequencies used in the main study. B, Difference between the average SSVEP amplitudes at 9, 11, and 13 Hz, and 1, 3, and 5 Hz (marked as asterisks), under different hypotheses, as discussed in C–F. Cyan and magenta bars correspond to the conditions where the target frequency was 7 and 15 Hz, respectively. C, Nonspecific interaction: cyan and magenta curves depict 7 and 15 Hz target frequency responses as a function of the temporal frequency of mask grating. The green curve is the underlying suppression function, which is a horizontal line indicating that the suppression of target SSVEP response is independent of the mask frequency. Solid dots are the different mask frequencies used in this study, whereas the circled data are the frequencies used in our previous study (we had actually used 8 and 16 Hz target frequencies in the previous study, but shifted to 7 and 15 Hz). D, SSVEP gain-specific interaction: the suppression function is same as the SSVEP response function, indicating the strongest suppression for the temporal frequency range that elicits the maximum SSVEP response, which is ∼10 Hz for both the target frequencies (7 Hz, cyan curve; 15 Hz, magenta curve). E, Low-frequency tuned interaction: the suppression signal (green curve) has more strength at progressively lower frequencies, potentially because of a low-pass filtering action on the normalization signal. F, Target frequency-dependent interaction: the suppression function varies with the target frequency and is maximum in the vicinity of the target frequency.
- Figure 2.
EEG amplitude response suppression of subject 1. A, The amplitude spectra are averaged over the good electrodes (N = 8). Each row indicates a different temporal frequency of mask grating (indicated at the extreme right of the fourth column) that is superimposed with a grating with a temporal frequency of 16 Hz (the target grating); the columns show different orientations of mask grating relative to the target grating. The blue trace is the 16 Hz “grating-only” condition (same trace in all plots). The number in the inset is the difference in amplitude at the target frequency (i.e., 32 Hz) between the grating-only condition and the plaid condition (i.e., between the blue traces and traces of other colors at 32 Hz). B, Difference between the grating-only condition and the plaid condition, as described above, plotted as a function of mask frequency for different orientations. C, Average difference between amplitudes above (18, 20, and 22 Hz) and below (10, 12, and 14 Hz) the target frequency (16 Hz), for different orientation difference conditions. The error bars indicate the SEM along with the significance level. ***p < 0.001; **p < 0.01; *p < 0.05.
- Figure 3.
Averaged EEG amplitude response suppression of all subjects. A, B, Same as Figure 2, A and B, but for data averaged over all usable subjects (N = 8). C, Same as B, but after adding data from eight good subjects who participated in experiment 2. The amplitude response is plotted as a function of delta frequency (mask frequency – target frequency), since for the second experiment the target frequency was 15 Hz. D, Same as Figure 2C, but for data averaged across 16 subjects.
- Figure 4.
Averaged EEG amplitude response suppression of all subjects for a wider range of mask frequencies. A, B, Same format as in Figure 3, A and B, but for eight usable subjects who participated in experiment 2, which had a wider range of mask frequencies and a target frequency of 15 Hz. C, The average difference between responses obtained for plaids with mask frequencies of 9, 11, and 13 Hz and mask frequencies of 1, 3, and 5 Hz (as indicated in solid circles; Fig. 1B magenta bars shows this value under different hypotheses).
- Figure 5.
Suppression profile for different target frequencies. A, SSVEP amplitude suppression for target frequencies 7, 11, and 15 Hz in monkey recordings, and 7 and 15 Hz in human recordings as a function of mask temporal frequency in the parallel condition. B, Same as A, but for the orthogonal condition. C, For 7 and 15 Hz target frequencies, the average difference between responses obtained for plaids with mask frequencies of 8–13 Hz and mask frequencies of 1–6 Hz in monkey recordings. In human recordings, the average difference between responses obtained for plaids with mask frequencies of 9, 11, and 13 Hz and mask frequencies of 1, 3, and 5 Hz. For 11 Hz target frequency in monkey recordings, the average difference between responses obtained for plaids with mask frequencies of 8–14 Hz (except at 11 Hz) and with mask frequencies of 1–6 Hz (as indicated in solid circles). M1: monkey 1; M2: monkey 2.
Movies
- Movie 1.
Parallel condition: target grating is at 100% contrast, 4 cycles/° spatial frequency, 0° orientation, and 15 Hz temporal frequency. Mask grating is at 100% contrast, 4 cycles/° spatial frequency, 0° orientation, and 11 Hz temporal frequency.
- Movie 2.
Orthogonal condition: Same as Movie 1 except that mask grating is at 90° orientation.
- Movie 3.
One trial with three stimuli: target grating parameters are the same as in Movie 1. The orientation and temporal frequency of the three mask gratings are as follows: 0°, 11 Hz; 90°, 13 Hz; and 90°, 15 Hz. Each stimulus is presented for 800 ms, with 700 ms as the interstimulus duration.
