Running an Eye tracking experiment with E-Prime
When using E-Prime with a SMI eye tracker, E-Prime should communicate with iView X, the eye tracking software, to start and stop the recording, indicate the start of each trial, specify the stimulus used and finally save the data. The way SMI prefer to do this is by using an ethernet connection and the UDP protocol, but E-Prime cannot handle this. The only way, at the moment, is by using the serial port. To do this you wil have to add the following things to your E-Prime script:
1 - Create a 'Serial' device, by going to 'Experiment object' properties, then selecting the 'Devices' tab, then 'Add' and 'Serial'. The default settings should work. In the next sections I assume you have named the device 'Serial'.
2 - At the start of your experiment, when you want the eye tracker to start recording, add these lines, in an inline object:
' Flush serial connection and clear eye tracker recording buffer Serial.FlushOutBuffer dim strData as string strData = "ET_CLR" & Chr(10) & Chr(13) Serial.WriteString strData ' Start eye tracker recording strData = "ET_REC" & Chr(10) & Chr(13) Serial.WriteString strData
3 - At the start of each trial, or just before your main stimulus is being presented, add a 'remark line', preferably with your stimulus name as an argument:
Dim strData As String
strData = "ET_REM " & c.GetAttrib("stim") & Chr(10) & Chr(13)
Serial.WriteString strData4 - Finally, at the end of th experiment put these lines in an inline object:
' Stop eye tracking recording
strData = "ET_STP" & Chr(10) & Chr(13)
Serial.WriteString strData
' Save eyetracking data in a file with a subject, session etc.
dim filename as string
fileName = str(c.GetAttrib("Subject")) & "_" & str(c.GetAttrib("Session")) & ".idf"
strData = "ET_SAV C:\\" & fileName & Chr(10) & Chr(13)
Serial.WriteString strDataObviously, the filename can be changed to whatever is best for you. Note that iView X cannot save to a directory that doesn't exist, so make sure to either create the correct directory, or write to root.
Running the script
When running the script you should go through these steps:
1 - Switch on the eye tracking hardware and install your subject.
2 - Start the iView X program on the eye tracking computer.
3 - Make sure the eye picture looks good and the eye gaze is correctly tracked. Verify this by asking the subject to look at all 4 corners of the screen.
4 - Start the 'WinCal' program on the srtimulus presentation computer.
5 - Click on the calibration button in iView X. The stimulus presentation machine should now present a screen with a calibration dot. Press space on the eye tracking machine to start calibration. The dot should move around the screen.
6 - After succesful calibration, switch off WinCal on the stimulus presentation machine.
7 - Start your E-Prime script. iView X should indicate that it is recording.