Electrode impedance was kept below 5 kΩ. EEG was amplified with a gain of 500 K, bandpass filtered at 0.05–100 Hz, and digitized at a sampling rate of 500 Hz. The signals on these electrodes were referenced online to the nose and were rereferenced this website offline to the average of two mastoids. Using Brain Vision Analyzer (Brain Products, Munich, Germany), eye-blink

artifacts were semi-automatically corrected using the procedure described by Gratton et al. (1983). EEG epochs lasting 350 ms, starting at 100 ms before the texture stimulus onset, were made. They were selectively averaged according to the orientation contrast. Epochs with EEG or residual EOG exceeding ±50 μV at any electrode were excluded from the average. The average waveforms were low-pass filtered at 40 Hz and baseline corrected with respect to the average voltage during the 100-ms prestimulus interval. The C1 response was apparent between 60 and 90 ms after stimulus onset. To select electrodes for the C1 amplitude and latency analysis, grand averaged ERPs were

made by averaging across subjects and orientation contrasts. Posterior electrodes, including CP1, CPz, CP2, P1, Pz, and P2, had the largest C1 amplitudes. To quantify the C1 amplitude for each subject, Selleck Epigenetic inhibitor the mean amplitude of the five sampling points around the C1 peak was first calculated for each of these six electrodes, and this mean was then averaged across the six electrodes. The C1 latency was the mean of the peak latencies across these six electrodes. Estimation of the dipole sources was performed using the BESA algorithm as described by Clark and Hillyard (1996) and Frey et al. (2010). The C1 component was modeled based jointly on the grand-averaged waveforms elicited by texture stimuli with the four orientation contrasts. The waveform in the interval between 62 and 82 ms was simulated with two dipoles, one in each hemisphere, which were constrained to have mirror-symmetrical locations, but allowed to vary in orientation. The initial

starting positions of dipoles were randomly chosen and using different starting locations yielded high similar dipole configurations. The event-related fMRI experiment consisted of Metalloexopeptidase four functional scans of 128 continuous trials. Each scan began with 6 s fixation and lasted 274 s. There were four types of trials—orientation contrast trials (7.5°, 15°, and 90°) and fixation trial. In an orientation contrast trial, a texture stimulus was presented for 50 ms, followed by a 100 ms mask and 1,850 ms fixation. Similar to the 2AFC experiment, subjects were asked to indicate the location of the foreground region, which was left to the fixation in one half of orientation contrast trials and right in the other half at random. In a fixation trial, only the fixation point was presented for 2 s. In a scan, there were 32 trials for each type of trial.