I am soliciting opinions on evaluating different projection and display
systems suitable for fMRI experiments. Although we have sought the views
of a few experts, I thought a more general query might be useful. Assuming
sufficent interest (and responses), we'll post a summary of answers next
week to CVNet.
Summary question: Please send opinions on models of LCD projectors which
would be best suited for psychophysical experments. We're hoping to get
the best combination of native resolution (SXGA - 1280x1024), frequency
response (as close to 40 Hz), brightess and brightness/contrast uniformity
- in an inexpensive package. In addition, we would like to have a system
that has several different memory settings so that the system can be
calibrated for different experimental paradigms (since it is a multi-user
system). Once these are determined, investigators could easily switch back
and forth without needing to set individual brightness/contrast etc
settings.
Experience with or creative suggestions for non LCD projection systems are
also sought.
Background:
Most fMRI labs use a combination of mirrors, LCD projectors and
back-projection or front-projection screens to present computer generated
stimulus to their naive or not so naive subjects. LCD systems are
minimally affected by the high-field magnetic enviroment, but CRT systems
suffer because of the differential effects of the magnetic field on the
electron beam. There are exceptions - some labs have reportedly designed
mu-metal shielded CRT monitors in combination with a periscope, other labs
have custom-built binoculars with large format LCD screens.
The native properties of the LCD systems don't lend
themselves well to psychophysics. The biggest problem is that the control
elements (TFT) attached to each LCD cell have a minimum 25msec response
time. This presents difficulties for experiments that use moving stimuli.
In addition, most LCD projectors resample the analogue input signal in
some fashion. This can (and usually does) introduce problems with video
synchronisation.
While an ideal solution might be to use a CRT projector such as a
Barcographics 1209s (www.barco.com/projecti/products/graphics/9000972.htm)
this presents it's own set of problems.
Please email your replies to sean@nmr.mgh.harvard.edu. I'll post a summary
of responses sometime next week.
Sean
(Thanks to Steve Elliot at Cambridge Research for explaining the problems
with the TFT elements to me).
--------------------------------------------------------
Sean Marrett email: sean@nmr.mgh.harvard.edu
MGH NMR Center. tel:(617)-726-8791
Building 149 (2301), 13th Street fax:(617)-726-7422
Charlestown, MA 02129 USA