Usage
TEMPO is able to read EEG recordings in EDF (European Data Format) format. EDF is simple and flexible standard format for exchange and storage of simultaneously recorded physical signals. EDF specification, as well as pointers to converters from other commonly used EEG formats to EDF format, are available at http://www.hsr.nl/edf/.
TEMPO expects file name to be specified trough file selection dialog, that is in turn activated using first button in row of buttons in bottom right corner of application main window.
TEMPO has extensive error checking included. However, error reporting is rather primitive for now: when encountering unrecoverable error, TEMPO will print the error code and will terminate then. This information is intended for TEMPO developers, so please include it when reporting problem. More user friendly error reporting mechanism will be eventually added later.
Thus, if for any reason (file does not exist, user does not have appropriate permissions to access file) TEMPO is unable to access to specified EDF file, the error code will be printed and program will be terminated. Otherwise, TEMPO will proceed to read EDF file header. Some important checks are performed on file header too. First, version of EDF data format is checked and then electrode names for EEG from EDF file are compared to names of electrodes known to TEMPO. EDF format is very flexible regarding types and arrangements of recorded signals. However, TEMPO is able to recognize only signals from electrodes named according to so called 10-10 (and, by inclusion, 10-20) international standard. EDF file must contain signals from at least six alike electrodes in order to have TEMPO to accept file for mapping; otherwise, TEMPO will report an error.
Actually, names (and positions) of electrodes are read from an external file. This file is in an ASCII format and it is possible to support additional electrodes. New electrode names are easy to add, but electrode positions should be precisely specified there, and that could be hard part. Thus, it is recommended to stick with 10-10 arrangement and to give appropriate names to electrodes in EDF file.
If everything fine with EDF file header, TEMPO will proceed with reading scalp and face models (these models are, like electrodes information, stored in external files in an ASCII format) and will then show application main window. The screen-shot of TEMPO main window is given in Figure 1.
Left part of TEMPO main window is occupied by visualization window, displaying current topographic map. User could left click and drag mouse here, to have head model rotated. Dragging to left and right corresponds approximately to rotating head model around world y-axis (from head center to up) in 3D and dragging to up and down corresponds approximately to rotation head model around world x-axis (from head center to right).
Right part of TEMPO main window is occupied by five groups of graphical user interface controls. Each control has a tool-tip explaining its purpose, and each control will be described in more details here. First four groups are enclosed by corresponding frames and fifth group consists of four buttons in bottom right corner of main window. First frame is intended to display information about recording only. Following informations from EDF file header are displayed here:
- local patient identification
- local recording identification
- start date and time of recording
Second frame contains controls for selection of score to be topographically mapped and for adjusting its parameters. As for now, TEMPO supports three scores:
- raw EEG potential
- amplitude of potential DFT (Discrete Fourier Transform) values
- phase of potential DFT values
First control in scores frame is menu for score selection (menu items are also showing score units - microvolts or radians). Other two controls are intended for further specification of DFT related scores and are disabled when raw potential selected in first control. Second control in scores frame is menu for number of raw potential samples used to calculate signal DFT (this number is often called DFT window or simply window). Allowed values are 128, 256 and 512 samples (FFT algorithm is used for DFT calculation, thus number of samples should be power of 2). Samples to calculate DFT are always taken from current point in input file backwards (thus, current time, that is representing current point in input file, could be adjusted when changing current score or DFT window , if this is necessary to have enough samples before current point in input file for DFT calculation). Third control in scores frame is spin button for selecting current frequency for DFT scores. For each input vector of raw potential samples, DFT calculation produces output vector of same length of complex numbers. Each of these numbers corresponds to single frequency in input signal spectrum and only values for one specific frequency could be mapped at a time. Third control in scores frame is for specifying this frequency. The upper range of this spin button is always set according to Nyquist theorem of signal sampling: it is eventually adjusted when DFT window changes, but is always less or equal than one half of signal sampling frequency.
Third frame contains controls pertaining to color legend. Lower half of values for given score are mapped to colors between blue and green, upper half of values are mapped to colors between green and red. Frame with legend controls contains also two spin buttons for controlling lowest (mapped to pure blue) and highest (mapped to pure red) score values represented by legend. TEMPO is using simple heuristic for calculating lowest and highest score value for raw potential score and highest values for DFT amplitudes (lowest value for each DFT amplitude is always 0 and DFT phase values are always between -pi and pi radians). Namely, each time when new score requested, TEMPO is calculating number of score values for each recognized signal from random positions in EEG file, and then using these values estimates lowest and highest score values for legend. Score values that are later found to be lower than lowest values or higher that highest values are clamped and mapped to pure blue and red color respectively. This heuristic give pretty good results in most cases, but depending on EEG file contents it could also miss completely. In these cases, spin buttons could be used to adjust boundaries. Current low boundary could be set anywhere between twice times initial lowest value and current high boundary, and high boundary could be set anywhere between current low boundary and twice times initial highest value. All of above considered, user has lots of freedom in selecting most appropriate resolution regarding mapping score values to color map. Low and high boundaries are remember for each score separately. Thus, when score changes using corresponding menu from score controls frame, boundaries for selected score are restored automatically.
Fourth frame contains time related controls. First row of these controls is showing EEG file sampling frequency. Next row contains a spin button representing current time in seconds. When animation is ongoing, this button is disabled, but continuously updating, showing time that corresponds to current map, starting from beginning of the file. When animation stopped, user could use this button to jump to arbitrary position in the input file. As mentioned above, TEMPO also could adjust this value automatically, if necessary to have appropriate number of samples before current position in order to be able to calculate DFT related scores. Third row of time controls contains spin button for selecting animation step, i.e. for how many samples current position is advanced between generating two successive topographic maps. Like current time control, this control is disabled while animation is ongoing, but while animation stopped it could be used to select coarser time resolution. Three buttons for animation control appear in next row of time controls. First button is for starting animation, second button is for pausing animation and third button is intended to stop (pause and reset current time to smallest possible value) animation. Only one of these three buttons could be active at the same moment. TEMPO is also stopping animation automatically when encountering end of the EEG file. Last row of time controls contains slider for adjusting animation speed, i.e. how fast (or slow) the animation will run respective to real time flow.
Last group of controls on the right side of TEMPO main window consists of four push buttons. First button is, as mentioned above, for opening new EDF file. Second button is intended for saving current topographic map in PNG format. Third button is intended to launch help browser and display help pages that you are now looking at. Finally, pressing fourth button quits TEMPO application.