EyeLink II Scene Camera User Manual
©
2004-2007 SR Research Ltd.
45
starting a recording session, click “View -> Preferences”. Select the “Advanced”
tab. Check whether the base address of the parallel port is correctly set (LPT1
is typically assigned to the base address 0x378, while LPT2 is assigned to
0x278). Enable the “Start” (sending out a synchronization signal when
SceneLink starts recording), “End” (sending out a signal when SceneLink stops
recording), and “Clear” boxes (sending out a clearing signal 50 msec following
the START or END signal, or BOTH). Now, specify the register (typically “DATA”
register of the parallel port) where the signals should be sent and the intended
TTL Values. Note that the base address and value fields expect a hexadecimal
number (so the user should enter 0x378 instead of 378). The outgoing TTL
signal is sent immediately after the eye tracker starts or stops recording and
marked with a “SCENELINK_TTL [OUT] START_TTL” or “SCENELINK_TTL [OUT]
END_TTL” message in the EDF file.
It is also possible to control the start and end of a SceneLink recording by
external triggers received through the parallel port of the display computer. The
address is typically set to the “STATUS” register of the parallel port. An
incoming signal that matches the prespecified value will initiate a short lead in
the video recording and then start the tracker recording. This input signal is
marked with a “SCENELINK_TTL [IN] START_TTL” message in the EDF file. The
end signal will immediately stop the eye tracker recording; this signal is marked
with a “SCENELINK_TTL [IN] END_TTL” message in the data file. Please make
sure both the start and end trigger signals last at least 50 ms for the SceneLink
display PC to pick up reliably.
4.8.3 Performing Online Drift Correction
During recording, if the user notices excessive drifts in the gaze cursor drawing,
a runtime drift correction can be perform from either the display PC or from the
host PC as shown below.
Important
: Please be aware that for a recording with
scene camera option, the “Drift Correct” button in the Camera Setup screen
behaves differently from a recording without using the scene camera. After
performing a depth correction, clicking this button will bring up the Scenecam
Depth Setup Screen and erase the original offset and slope parameters of the
fitting function. So please avoid clicking on the “Drift Correct” button on the
Camera Setup screen. Use one of the following two approaches instead.
4.8.3.1
Online Drift Correction from the Display PC
To perform an online drift correction from the SceneLink application, first
specify a fixation target within the calibrated space at a particular depth
(preferably at the calibration depth) and ask the participant to fixate on the
target precisely. While the participant is fixating on the target, move the display
PC mouse, place the cursor over the fixation target and click the right mouse
button once. The drift correction may fail if there is no stable fixation data or if
