# Last edited on 2017-09-19 15:54:38 by jstolfi MAILED: * Trigger pulses are 1 frame duration, right? * CZ is always zero. * Just to confirm: Is CZ same as VREF in the electrode diagram (surrounded by C7 C106 C80 C55 C31)? Or is it the unlabeled white disk a little further back (surrounded by C55 C79 C78 C62 C61 C54)? * Too much line noise (and harmonics); about ±240 uV amplitude. * Should use analog filter to kill anything above 40 Hz. It is noise, right? TO MAIL: * * Extracted run files We worked around the problems above, and we extracted all runs into separate files (in the "raw-runs" directory). Each start-of-stimulus marker in the ".raw" file gave one separate run file. Every file has exactly 3500 frames (7 seconds), and the stimulus phase (as assumed from the start-of-stimulus markers) starts after exactly 1750 frames (3.5 seconds) after the first extracted one. The fixation and stimulus phases of each run, whether inferred from the marker pulses or abitrarily truncated, are indicated by two new marker channels "FX" and "ST". Each of these channels is positive during the entire corresponding phase, and zero otherwise. The channel "ST" goes up immediately after the "FX" channel goes down. The duration of the fixation phases varies from 3.010 to 3.346 seconds, as defined by the markers in the ".raw" files; except for subject 11 block 1 run 1 (s011_r00101.txt) that has only 2.2 seconds of fixation, and subject 12 block 6 run 1 (s012_r00601.txt) that has the fixation phase arbitrarily set to 3.360 seconds, even though it probably was shorter. In the analyses, it may be wise to exclude those two runs. In the extracted run files, the duration of the stimulus phase generally varies between 2.988 and 3.002 seconds, with a handful extending up to 3.016 seconds. Note however that these lengths may have been defined by the manual editing of the ".raw" files. The exceptions are the end-of-block runs of all subjects, and all runs in S21.raw, that were truncated to 3.020 seconds by the extraction program. In each extracted file, the samples in each individual channel were shifted so that their average over the indicated "FX" and "ST" phases is zero. An attempt was made to ignore apparent outliers when computing the average. Note that this operation was applied to each channel independently. * Following applies to after filtering. * Substantial drift in some channels. Averaging them is not good: just one of those drifters will ruin the average. * Lots of blinking (most runs have a blink in either the fixation or stimulus phase, sometimes both). * Blinks have a regular pattern with few exceptions. Each blink lasts around 4.5 seconds, almost never more than 6.0. Some electrodes rise by 100-200 uV positive while others get to 50-100 uV negative. Typically the rise is very fast (1/4 of the blink) and the return to normal slower. There are a few mini-blinks (shorter and with smaller amplitude) and a few mega-blinks (where the peak is sustained by 0.5 to 1.0 seconds). * Principal component analysis of the isolated blinks has two notable PCs. P000 (strength 159 uV for subject s013) is a strong spot in the frontal area with a faint signal of opposite polarity in the rest of the head. P001 (strength 59 uV for s013) is a broad "crown" around the head, falling to zero on the apex and around the edges. Both are surprisingly symmetric and consistent across the 2 subjects. The next P002, P003, P004 seem to be less defined, and are different among the two subjcts. See flt-runs-B/s{013,014}_blinks_P{000,001,002,003,004}_eig_f000000.png * Blinks are much more common about 0.5 to 0.7 seconds after the start of the fixation phase (tF). They are less common in the 0.7 seconds after start of stimulus phase (tS) then increase from 0.7 to 1.9 sec after tS. See flt-runs-B/blinks-clean_hist.png * Excluding runs with crazy electrodes and blinks in the sensitive region (last 1 sec of fixation and 3 secs of stimulus) leaves only 91 runs of subject 013 (36%) and 16 runs of subject 014 (6.3%). * Blinks are very different in subj 13 and subj 14. Both have a principal mode with positive in the forehead and slightly opposite elsewhere, which is the blink proper. Both then have a crown mode that seems to pulsate at 10 Hz. Subject 14 has another mode thet is strongly centered on the nose, also for blinks. * Peculiar runs: 13 206 near-blink @5.5 13 217 short blink @?? 13 223 some electrodes are crazy 13 603 some electrodes are crazy 13 126 three blinks in short succession 13 401 totally crazy 13 431 quasi-blink @0.8 13 501 totally crazy; large "alpha waves" 13 519 mixed blinks/motion? 13 528 extended blink @2.5, @0.9 13 624 extended and strong blink @1.0 13 713 two merged blinks 13 714 extra-strong blink 13 716 two merged blinks @0.7 13 719 mixed blinks/motion? 13 720 mixed blinks/motion? 13 826 two blinks close together (0.47 sec apart) 14 118 three blinks of different size 14 131 strange blink @4.4 14 227 strange blink @4.2 14 521 "negative blink" @0.6 14 613 blink train? @4.7--6.4 14 614 strong alpha @1.5 14 718 totally crazy 14 827 large "alpha waves" @4.5 * Crazy electrodes happen often on the first run of a block. * The signal around 10-12 Hz ("alpha waves"?) seems to be common mode hence should be deleted? * Correlation is decreasing with delay because of common mode * Saccades? * Averaging will not work of reaction times are variable. * I believe that the alpha signal (about 10 Hz, "bouncing" front to-back) appears when a person is awake with eyes closed. Does the alpha signal appear when the subject is open-eyed but in total darkness? * Physiological tremors 1-12 Hz: http://www.medscape.org/viewarticle/572015 http://brain.oxfordjournals.org/content/123/8/1545.long http://www.diku.dk/~panic/eyegaze/node16.html If an image is artificially fixed on the retina it disappears, but physiological nystagmus causes every point of the retinal image to move approximately the distance between two adjacent foveal cones in 0.1 seconds. Physiological nystagmus actually occurs during a fixation period, is involuntary and generally moves the eye less than 1°. http://www.sciencedirect.com/science/article/pii/S0042698998003228 Ocular microtremor (OMT) is a high frequency tremor of the eyes present during fixation and probably related to brainstem activity (Coakley, D. (1983). Minute eye movement and brain stem function. CRC Press, FL.). Published observations on the frequency of OMT have varied widely. Ocular microtremor was recorded in 105 normal healthy subjects using the Piezoelectric strain gauge technique. The dominant frequency content of a signal was determined using the peak counting method. Values recorded ranged from 70 to 103 Hz, the mean frequency being 83.68 Hz (S.D.±5.78 Hz). * Eye tremors 80 Hz: