CbuStimulusDelivery - CBU MRI facility Wiki

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Revision 11 as of 2006-10-06 12:39:27

location: CbuStimulusDelivery

Stimulus delivery in the CBU Tim Trio

Stimulus delivery computers

There are three stimulus delivery computers. All have identical software and receive the scanner trigger pulse and button box responses.

Software

The machines run Windows XP. Installed software is Matlab 7, Eprime, Visual Basic, Cogent, DMDX.

Synchronising with scanner

DMDX will recognise the signal from the Keithly I/O card. However, since the trigger pulse is of duration 6ms (rather than 50ms as before), you will need to use the keyword <id qpio12 1> in the topline of your script to ensure that DMDX detects trigger pulses reliably. There are more notes on using DMDX [http://www.mrc-cbu.cam.ac.uk/~mattd/fmri_dmdx.html here].

From other environments (Eprime/Matlab/VB), you may use the [http://www.mrc-cbu.cam.ac.uk/~rhodri/vb ScannerSync] library. This allows you to synchronise, and to collect button box responses.

Mimic machine

In the CBU computer user room there is a "CBU mimic" configured exactly as the stimulus delivery machines, and with a pulse generator to simulator the scanner trigger, and a response box. You must test your programs thoroughly on the mimic before running any experiment.

Pre-testing machine

There is another mimic machine in the imaging centre, which you may use for pre-testing in experiments that require a training session just before the scan. You'll then need to have two experiments attend.

Visual presentation:Christie video projector

Visual presentation: Christie video projector

Recommended resolution 1024x768

Refresh rate 60 Hz. Please do not change this parameter. Although the projector will accept inputs up to 100 Hz, it will not actually produce output at these higher rates, but instead, sub-sample down to a rate just above 60 Hz.

Latency: There is a fixed temporal delay between computer refresh and actual display of a little less than 20 ms. If you don't account for this, your RTs are probably around 20 ms shorter than you think they are.

Size: Distance between MRI screen and mid-point of mirror = 823mm Approx distance between eyes and mid-point of mirror ~ 90mm Width of full-screen display on MRI screen = 268mm

Using DMDX

All machines should contain a small DMDX testscript, which should be used to check the proper functioning of the button box, the headphones and the projection system.

There are three video modes available for DMDX:

  • 1024 * 768 16 bit 0 Hz
  • 1024 * 768 16 bit 60 Hz
  • 1024 * 768 32 bit 60 Hz

The first mode is only installed for compatibility. It should not be used. The 0 Hz indicates that the 'default' refresh rate is used, which is usually the refresh rate that is set for Windows. This will always be 60 Hz too, so identical to the second mode. But it is still better to explicitly set the refresh rate. People have had trouble with this before, when someone changed the Windows display settings. People do fiddle.

The second mode is the one that has always been recommended for most users.

The third one will give better colour, so should be used when pictures are being presented. It also has the advantage that it is completely identical to the Windows settings, meaning that there will be no mode switching, which could prevent problems, certainly with flat screens and projectors.

So, to summarise, the best mode to use is the last one, which should be specified in your DMDX script like this:

<VideoMode 1024, 768, 768, 32, 60>

or

      <vm 1024, 768, 768, 32, 60>

Additionally, I would like to repeat the need to use QPIO12 with the current setup, instead of PIO12.

      <InputDevice "QPIO12">

or

      <id "QPIO12">

Auditory presentation

Option 1: Siemens tube phones

For many experiments in the scanner that require sound, but not too much audio fidelity, the built-in Siemens tube phones are sufficient.

Frequency response

Sound level set to max on PC and 9 bars on the scanner. Tones at various frequencies were then presented. The levels (in dB SPL) of the primary (H1) and first and second harmonics were:

Freq (Hz)

H1

H2

H3

250

92.97

73.86

74.39

500

98.07

74.34

65.58

1000

98.10

59.20

27.16

2000

68.61

32.10

9.38

3000

47.24

5.0

15.82

4000

49.99

5.05

13.53

6000

27.88

11.57

7.97

8000

23.03

8.50

7.78

The full frequency response as measured using periodic noise from a spectrum analyzer:

http://www.mrc-cbu.cam.ac.uk/Imaging/siemens_headphones.jpg

Headphone simulator/pre-emphasis tool Here is a tool that allows you to do two things: (1) approximately simulate what your stimuli will sound like in the scanner (2) pre-emphasise your stimuli, boosting the frequencies that will be reduced by the presentation system

A new tool for pre-emphasis has been produced by Christopher Long, which does not produce a subtle ringing artefact produced by the previous tool. This is [http://www.mrc-cbu.cam.ac.uk/~chrisl/compfilter.html described here]

The old tool is described on [http://www.mrc-cbu.cam.ac.uk/~rhodri/headphonesim.htm this page]:

Option 2: Etymotic ER3

This alternative pneumatic tube presentation system offers higher quality. It is being installed in Mar 2006.

Frequency response

Gary Chandler kindly made these measurements:

LEFT

RIGHT

Amplitude dB SPL

Amplitude dB SPL

Freq (Hz)

H1

H2

H3

Freq (Hz)

H1

H2

H3

250

107.42

32.60

55.82

250

106.34

44.63

57.80

500

101.45

47.69

61.46

500

100.60

48.40

62.30

1000

102.99

56.90

53.20

1000

101.78

57.40

53.25

2000

94.66

61.65

25.43

2000

94.20

61.10

26.60

3000

90.59

50.25

20.10

3000

90.30

51.20

22.95

4000

85.30

30.40

2.38

4000

85.06

33.50

2.79

6000

62.82

20.54

0.30

6000

62.27

18.24

2.41

8000

45.28

6.53

5.90

8000

47.40

5.45

5.04

Headphone simulator/pre-emphasis tool I have made a tool that allows you to do two things: (1) approximately simulate what your stimuli will sound like in the scanner (2) pre-emphasise your stimuli, boosting the frequencies that will be reduced by the presentation system This tool is described on [http://www.mrc-cbu.cam.ac.uk/~rhodri/headphonesim.htm this page]

Future plans If these headphones will not satisfy your requirements, there are some other options in the pipeline:

  • A high quality electrostatic system from Nordic Neuro Labs. This is currently undergoing safety evaluation.

Button box

Button box

The default box has four buttons designed to be used from one hand or two.

Microphone

We have a Phonar optical noise cancelling microphone that allows clear recordings of spoken responses without much interference from the scanner noise.

Future plans

Future plans

Goggles & eye tracking: We are investigating a combined goggle presentation system and eye tracker from Nordic Neuro Labs. The current release date for this is July 2006.

Physiological measurements: When required software is installed on our system, we should be able to record cardiac and respiritory information.

Points of contact

Points of contact

Gary Chandler, who set up almost all of this equipment, is the best person to ask if you'd like an update on any changes to the system, or if something doesn't work.

If there is a piece of equipment you'd like to see added, please contact Rhodri Cusack or Gary Chandler.

If you would like access to the facility to install your programs or test the equipment, please contact Lucille Murby or the radiographers.

Last updated by Rhodri Cusack and Gary Chandler Feb 2006