eye tracking with media lab (case 19711)

[JEC]

It turns out that at least one eyetracker system is set up to automatically start and pause recording when Pin 1 on the parallel port is toggled between 1 and 0.

Pin 1 on the parallel port is the 'strobe' bit, according to

http://www.beyondlogic.org/spp/parallel.htm

The strobe bit is Bit 0 of the parallel printer's control register, which is found at the base address + 2. That is, if your printer is found at decimal 888, the control register is at 890.

So using the IOTester utlity found with every installation of MediaLab, you can send a test signal and see if it's working.

The proper MediaLab command would be

(d5,<1:890:5000>)

For a five second low-to-high pulse on the strobe line.

[jarvis24]

For a sample MediaLab input file, see:

http://www.empirisoft.com/support/showthread.php?t=152

[jarvis24]

[edited from support email]
I have a question about the timestamp function of MediaLab. We are trying to synchronize eye tracking data with video data. In order to do this, I need to know exactly when MediaLab is making the stamp. It says it does so at the onset of the stimulus; however, I'm not sure if this means during the "purple screen", where it is opening the file, or when the video actually starts playing. The latter would be ideal.

[jarvis24]

Whether or not you using a MediaLab "timestamp" or a MediaLab TTL signal, the signal will be sent at the onset of the trial (as opposed to when anything happens during the trial like a video). In contrast, with DirectRT, a TTL signal can be sent in near perfect synch with the onset of any stimulus within a trial.

[JEC]

UPDATE: The friendly folks at Applied Science Laboratories were kind enough to share some additional information on this topic.

The material I've posted above is correct with the following qualifications:

1. You cannot use a 25 pin cable from Radio Shack. Use the cable supplied by ASL.

2. ASL Record bit is parallel (LPT) port bit 7 (not bit 1). Recording will be ON as long as this bit is high, and be paused during any time that the bit is low. If you only turn on bit 7, this is decimal 128, hex 80, binary 1000 0000. It won't matter whether other bits are on or not, they can be used for other things if desired. Turning all the bits on (decimal 255, hex FF, binary 1111 1111), as described in the second web link, will certainly start "auto record", but only bit 7 is actually needed.

3. If desired, it is also possible to use parallel port bit 6 to open and close data files. If this option is selected, a file named with the current date and time will open when bit 6 goes high, and will remain open as long as bit 6 stays high. The file will close when bit 6 goes low. Remember that a file can start recording only if the file is opened. If the auto file open option is used turn on bit 6 to open a file; turn on bits 6 and 7 to start recording; turn of bit 7 but leave bit 6 on to stop recording without closing the file; turn off bit 6 to
close the file.

[natxo]

Hi,

I've another question: is for sure that directRT send TTL signal by LPT port assigned like this: D7 D6 D5 D4 D3 D2 D1 D0 (I suppose this are pins from 1 to 8)? Should I ask someone to test this with an osciloscope?

I've to connect PC's LPT output with a D-15 port from a powerlab recording equipment, so I have to build up a connector to do this and I don't want to be "responsible [for] any explosion which may occur".

thanks a lot

[JEC]

Hi,

I've another question: is for sure that directRT send TTL signal by LPT port assigned like this: D7 D6 D5 D4 D3 D2 D1 D0 (I suppose this are pins from 1 to 8)? Should I ask someone to test this with an osciloscope?

I've to connect PC's LPT output with a D-15 port from a powerlab recording equipment, so I have to build up a connector to do this and I don't want to be "responsible [for] any explosion which may occur".

thanks a lot

There's a pinout of the parallel port here:

http://www.beyondlogic.org/spp/parallel.htm

An oscilloscope (or even just a voltmeter) is always a helpful tool to have.