ERP Data Analysis Part III: Figures and Movies

Transcription

1 ERP Data Analysis Part III: Figures and Movies Congratulations, you ve found significant results! Or maybe you haven t and just wanted to show that your data can make really nice pictures that may show a difference if there isn t actually one. In either case, this tutorial will help you generate fantastic graphics to make your presentation shine. To complete this tutorial you will need the following: A Mac running Mac OS X, Net Station (with hasp), and a copy of Adobe Illustrator CS. Often the first figures you want to make involve single electrode sites. Open up a Net Station file that has been through the pre-processing steps. Your final file should end in.ave for an averaged file. Next, select the following options under the View menu: Topo plot changes the view to show the electrodes and their approximate location on the scalp. Overlaid segments simply show all conditions (stimuli) overlapped, allowing you to easily see the different brain-responses to each stimulus. To adjust the scale click Fit under time and 1:1 under amplitude. You can also use the menus Time and Amplitude to adjust these settings. Your window should now look like this:

2 The next step is to identify a channel that you wish to show more closely. In this example we will look at channel 6, which sits slightly to the frontal midline. Double click on this channel in the window above and you should see the window below. Again you should adjust your time and amplitude options. An easy way to start is to have time 1:1 and amplitude as 1:1 and then adjust the amplitude to the level that you wish to display on your poster or paper. Take a screen shot now just in case, shiftapple-3 and keep it handy so you can easily remember which line is which condition as well as what the scale and amplitude are. This segment is length 700 milliseconds, with a 100-millisecond baseline. The first line represents the stimulus presentation and the 0- second marker, each line thereafter represents 100 milliseconds. These tick markers will become clearer in the Adobe Illustrator.

3 You may also filter your waveform to make it look cleaner at this point. To do so, go up to the Filter menu and select Filter Controls. The window below will appear to adjust the filter settings for the viewed file. Turn the filter controls on, and add a lowpass filter, adjust as necessary to make a waveform with desired smoothness. It is important to note that this filter is for illustrative purposes only; the statistics that you performed in chapter 2 (Using SPSS on ERP data) is on the waveform using the spectrum of 0.1 to 30Hz. The reason we filter here is to illustrate the differences found in the statistics. Keep in mind that adding a lowpass filter will delay most events in your waveform, in this case delaying the P300 nearly a hundred milliseconds. Now that you have the waveform the size and smoothness that you would like, it is time to export it for Adobe Illustrator. Using the File Menu, select Print Topo Plot. And now select PDF, Save as Post Script

4 Select the save location of your file and give it an appropriate name so that you can easily refer back to this file later. We are done using Net Station, so you can close it if you would like. Now Open Adobe Illustrator CS, and select Open Document or using the File Menu, select Open. Find your.ps file that you created out of Net Station and open it. A demonstration is shown below.

5 Note a few things, the file name is presented in the upper-left corner, the time window is shown in the upper-right corner, and the channel number is displayed next to the waveform. If you click anywhere on the image you will notice that everything becomes highlighted. Go up to the Object Menu and select Ungroup or Shift- Command-G. Now click on the horizontal bar just under the time display and the file name, hit delete on your keyboard. Select your filename and press delete. You may also delete the time range and the channel number if you would like. Also note that the figure is in black and white, this is normal and can actually be to our advantage. First we will look at how to make this waveform suitable for a black and white publication and then we can colorize them for a poster. Select one of the condition waveforms, and notice the pallets on the right side of the screen update their information. We want to make the top waveform as dark as the lower waveform, but represented as a dashed line. With Stroke selected on the pallet pictured below, click on the tiny arrow on the right side of the pallet and chose Show Options. This will give you the pallet shown below:

6 Check the Dashed Line checkbox as show above. The Dash setting that currently lists 12 in our figure is the easiest value to modify to change the characteristics of the line. Smaller numbers will cause more, and smaller, dashes to appear with less space between them. Larger numbers will cause fewer, but larger, dashes with larger spaces between. In this example I use the value of 4 for the dashed line. Be sure to adjust the weight of both lines to be 1 pt, and leave the second line as a solid line. Your figure should now look like the following: Now you will want to add a legend to your image so that readers will be able to easily identify which lines belong to which conditions. Consult your screen shot that you took earlier (or the original file) to check which line belongs to which condition. In Adobe Illustrator, click on one of the lines (with the arrow tool: ) to highlight it, now choose the line tool to draw your legend. Using the line tool draw an independent line somewhere else on the page. Notice it has the same characteristics as the line that was highlighted. Repeat the process, use the arrow tool to click on the other line, now select the line tool and draw another line with characteristics of your second line. Your figure should now look like the one below: If you are having trouble aligning the lines for your legend, you can use the tools across the top of the screen in Adobe Illustrator to help you. Now you should label your legend. Select the text tool and type in your legend names until your figure looks like the equivalent of the figure below:

7 If you would like to, you can modify the X-axis, add a Y-axis or put in some scale measures. Clicking on the X-axis will highlight it, dragging it vertically while draw the tic marks larger so that you can label them outside of the figure or have them extend through the figure as shown below: Or if you would now like to add color to one of the lines select it with the arrow tool and select a color in the swatch pallet on the right. Once you have made all of the finishing touches, it is time to save and export your image for adding to your Microsoft Word or Powerpoint documents. Using the File menu, select Save. Save as an Adobe Illustrator document in case you decide to change it later. Now under the File menu, select Export and choose either PNG or JPEG, depending on your preference. PNG is often smaller and better quality than JPEG, but is not always compatible with Windows applications. Select PNG, and you will get the following window: Select Medium or High resolution to be large enough and detailed enough for your presentation. Then under background select White otherwise it will be transparent and may not be what you d expect. Anti-Alias the image and press OK. Now name the file

8 and save it to an appropriate location. You could also save the file as a PDF for compatibility reasons the choice is up to you. To add your PNG file to Microsoft word or Powerpoint, just drag and drop the PNG file into your document or presentation. Below is the same figure in color: Also possible with time markers: And µv scale on the right side: The purpose of this tutorial was to give you an idea of the things you can do with Adobe Illustrator to make figures ready for publication. There are several other tips and tricks that can be used to make even better figures that will be covered in future chapters.