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getting_started:realtime_headlocalizer_neuromag [2013/04/29 14:49]
arjen [Step by step description for the visualization computer]
getting_started:realtime_headlocalizer_neuromag [2017/08/17 11:21] (current)
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-===== Practical issues and suggestions ===== 
-More details on the neuromag2ft command line parameters and its options are available [[development:​realtime:​neuromag|here]]. 
-It is recommended to install a {{:​getting_started:​switch-box-hd15-2-way-bestlink.jpg?​linkonly|VGA switch }} or 'video matrix'​ in the lab that can overwrite the signal from the stimulus presentation computer by that of the realtime visualization computer. This way the visualization can also be presented to the subject in the magnetically shielded room, allowing the subject to reposition himself/​herself. 
-The real-time head localizer for Neuromag systems uses a rigidbody constraint to optimally dipole fit the real time positions of the HPI coils, and thus of the subject'​s head. This means a hypothetical magnetic field distribution of all coils combined, is generated, based on their relative digitized positions as obtained from the neuromag fif file. The actual positions and orientations of the coils making up this rigid body are then approximated by fitting the resulting hypothetical field distribution to the actually recorded magnetic field distribution. It is, thus, important that all coils are working optimally. This can be [[faq:​how_can_i_visualize_the_neuromag_head_position_indicator_coils?​|checked offline]], using an already recorded dataset. 
-According to Neuromag documentation,​ frequencies of the HPI signals are 154, 158, 162, 166 and 170 Hz for the sampling rate of 600 Hz (low-pass filter at 200 Hz), or 293, 307, 314, 321 
-and 328 Hz for higher sampling rates. ​