Fastrak 3d digitizer

MEG was recorded continuously from a 306 triple sensor (204 planar gradiometers; 102 magnetometers) whole-head system (Elekta Neuromag, Helsinki, Finland) using a sampling rate of 1 kHz and an online band-bass filter between 0.1 and 300 Hz. The headshape of each individual participant was measured using a Polhemus FASTRAK 3D digitizer. Head position of the subject was recorded continuously using five localization coils (forehead, mastoids).
Data pre-processing was performed using the open-source Matlab toolbox Fieldtrip (www.fieldtriptoolbox.org; RRID:SCR_004849). First the continuous data were filtered (high-pass Butterworth filter at 1 Hz, low-pass Butterworth filter at 170 Hz, and DFT filter at 50, 100, and 150 Hz to remove line-noise artefacts in the signal), and downsampled to 256 Hz. Next, the data were epoched into segments of 1 s for subsequent analysis.
Rejection of trials containing artefacts and bad channels was performed using a semi-automatic procedure. First, outliers were rejected using a pre-screening based on the variance and range in each trial/channel. Then, algorithmically guided visual inspection of the raw data was performed to remove any remaining sources of noise.

MEG data were acquired with a 306-channel Neuromag VectorView system (Elekta-Neuromag Oy, Helsinki, Finland), which combines the focal sensitivity of 204 first-order planar gradiometers with the widespread sensitivity of 102 magnetometers. Eye movements and blinks were monitored with vertical and horizontal electrooculogram (EOG). The location of the head with respect to the sensors was determined using four head-position indicator coils attached to the scalp. A head-based MEG coordinate frame was established by locating fiduciary landmarks (nasion and preauricular points) with a Fastrak 3D digitizer (Polhemus, Colchester, VT). The data were digitized at 600 samples/second with an anti-aliasing low-pass filter set at 200 Hz.
MEG signals were averaged across trials for each condition, time-locked to the onset of the stimulus. A 34-ms delay between the time the computer sent an image and the time it was projected onto the screen was measured with a photodiode and subsequently taken into account when reporting the timing of measured activity. A 200-ms pre-stimulus period served as baseline. Trials to which subjects made an incorrect response and those that contained eye blinks exceeding 150 μV in peak-to-peak EOG amplitude or other artifacts were discarded from the average. The evoked responses were low-pass filtered at 40 Hz.

The field experiment was conducted in 2018 at the experimental field of Beijing Academy of Agriculture and Forestry Sciences (39°56′ N, 116°16′ E), to evaluate the performance of the proposed geometric modelling method. Four cultivars, including Aidan268 (AD268), Demeiya2 (DMY2), Jingke968 (JK968) and Zhengdan958 (ZD958), were selected and planted on 4th June at six plants per square metre, and row distance of 60 cm. Three shoots of each cultivar with representative morphometrics were selected at each growth stage (V6, V9, V13 and R1) for evaluation (Abendroth et al. 2011 ). A high-throughput phenotyping platform MVS-Pheno was used to obtain multi-view images of the selected shoots, and 3D point clouds were reconstructed (Wu et al. 2020 ). Morphological parameters were then obtained through skeleton extraction (Wu et al. 2019 (link)), and used to construct the maize shoot and population models. The phytomer number of each shoot was then determined. Fastrak 3D digitizer (Polhemus, Colchester, VT, USA) was used following the data acquisition standards to obtain 3D template data of all shoot phytomers, including skeletons and meshes. The templates were then added to the resource database. In addition, the leaf length and width of all the shoot phytomers were measured to validate the results.

MEG data were acquired inside a magnetically shielded room with a whole-head, adult-sized 306 channel Elekta Neuromag^® MEG system (Elekta Oy, Helsinki, Finland). Three anatomical landmarks (left and right preauricular points, nasion), five HPI coils, and approximately 100 additional points were digitized along the head surface using Fastrak^® 3D digitizer (Polhemus, Colchester, VT, USA) in order to construct an individual Cartesian head-centric coordinate system. Once the infant was seated calmly in a custom-made chair under the MEG helmet (Figure 1b), MEG data recording began with an analog band-pass filter of 0.03–330 Hz and a sampling rate of 1.2 kHz. During recording, infants were entertained with silent toys while a silent video of baby faces was played in the background. Infants’ head positions in relation to the sensor array were tracked continuously by extracting the magnetic fields emitted by HPI coils at frequencies between 83 and 323 Hz. Any channels with amplitudes lower than a certain level were marked as “flat”, removed (grad = 1 × 10⁻¹³; mag = 1 × 10⁻¹⁵), and reconstructed by applying the signal space separation (SSS) method [51 (link)] during preprocessing.