Stimulus Display
Visual stimuli
The video signal is split to the stimulus computer's screen and to a video projector (PANASONIC DLP projector, model PT-D7700E-K). The video projector beams the optical image via an opening in the MSR wall to a nonmagnetic back-projection screen (Flat panel LDC display). The diameter of the screen is 112 cm (44 inches). The angle, height, and viewing distance of the screen are adjustable. The screen is equipped with wheels. The actual field of view can be changed by moving the screen inside the shielded room.
- To switch on: push red '|' button (top left) and wait until it's heated (a couple of minutes). The correct channel is 'RGB 2'.
- To switch off: push red button right-hand of '|'. Push the button again (or on right arrrow and then 'enter') to confirm switching off.
Two CRT monitors are available as secondary devices.
How to use the projector
- The typical status of the projector is defined by the Default settings (see below).
- MEG users are allowed to change the projector settings (distance screen-subject, refresh rate) for specific needs of their experiment, PROVIDED that they move back to default settings when the experiment is done.
- Please note that changing the refresh rate may modify the position of the center of the screen and the focus.
- In general, MEG users should always check the quality and position of their visual stimulation before any experiment, and recalibrate the settings if needed (see below Settings recalibration).
Default settings:
Videoprojector:
- primary display device
- 60 Hz refresh rate (How to change refresh rate?)
- 1400 x 1050 resolution (Adjusting the resolution)
- Distance from the subject's eyes: 90 cm (position the end of the screen support leg closer to the MSR door at the "90 cm" mark on the floor)
- parameters settings:
- menu Position/Size: "Through" (your image size will be adapted to its input resolution)
- menu Picture:
* picture mode: manual
* contrast set to 30
* bright set to 0
* color set to 40
* tint set to 30
* color temp set to "user1"
* gamma set to "default"
* shift: V set to 30, H set to 382
Stimulation computer main display:
- secondary display device
- 60 Hz refresh rate
- 1400 x 1050 resolution
Settings recalibration
- Refresh rate
- Image position: On the remote control, press 'menu' -> 'position' -> 'shift', then use arrows to move the image vertically or horizontally. Practical advice: Ask a volunteer to sit in the MEG chair, lift her/him up as you would do for a normal subject, project a cross in the center of the screen directly on the face of the volunteer by removing the screen, and find the position for which the cross is central - typically on the volunteer's nose.
- Image focus: On the remote control, press 'lens', then use arrows to focus the image (calibrate by moving both the horizontal and vertical arrows). Practical advice: Ask a volunteer to sit in the MEG chair, project some words on the screen and ask her/him to evaluate the focus (since the remote control cannot be moved closed to the gantry because it's magnetic, you will only be able to see the back of the screen).
Auditory stimuli
The audio system is an HiFi-quality artifact-free headphone system with wide frequency response.
The frequency response measured from the subject headphones is flat within 3 dB to about 10 kHz (see Figure below).
Auditory stimuli are conveyed through earplugs by an audio amplifier connected to the stimulation PC. A loudspeaker is also available, but it is not connected yet (please ask MEG staff if you need to use it).
Default settings:
Audio amplifier:
- source set to CD
- sound intensity set to 45
- loudspeakers and audio amplifier are both connected to the stim pc (via splitter)
Audio-visual synchronisation:
- visual stimuli are visible on the projection screen about 33 milliseconds *after* the sound. This is due to the fact that 2 visual frames (16 ms x 2) are buffered by the projector. Adjust your timing accordingly if audiovisual synchronization is crucial.