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MEGCOMMUNITY  November 2012

MEGCOMMUNITY November 2012

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Subject:

Re: LCD screen in MEG chamber

From:

"Okada, Yoshio" <[log in to unmask]>

Reply-To:

Okada, Yoshio

Date:

Thu, 15 Nov 2012 17:52:03 +0000

Content-Type:

text/plain

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Actually I had meant OLED, which  is a new type of LED. By the way LED consumes less power than LCD and thus they might be less noisy. We are testing these devices and new elegant projectors as well.



What I do not like is the set of mirrors, which to me is very archaic and the severe constraints introduced by the screen for producing versatile visual stimuli.



Does anyone know if there is a device that takes a coherent fiber optic bundle to bring in an image data into the MSR, producing a small image in a device and then use a lens system to project that to a bigger screen that can be placed anywhere in front of the subject? This will eliminate rf leakage and it will not bother children unlike a pair of goggles, thus easier for children.



yoshio



________________________________
From: Discussion list for international MEG community [[log in to unmask]] on behalf of Christopher Bailey [[log in to unmask]]
Sent: Thursday, November 15, 2012 7:51 AM
To: [log in to unmask]
Subject: Re: [megcommunity] LCD screen in MEG chamber

Hi, this is an interesting discussion.

I would also recommend only using the 60 Hz refresh rate. One reason is that your display card-driver-combination is almost guaranteed to work at this rate, but not necessarily higher. In addition, with the resolutions we are using these days, using a higher refresh rate may start to saturate the bandwidth of a single-link DVI cable: at 85 Hz you can maximally achieve a resolution of ca. 1347 x 1010 pixels (assuming a 4x3 aspect ratio).

We have a Panasonic PT-D10000E (3-chip DLP), which also has practically no jitter (sub-ms) and a very stable 1 frame "delay" using the pre-loading features of Presentation/E-Prime/Psychopy/etc at 60 Hz.

I'd like to back Yoshio up a bit here... DLP's are a fine tool and once you understand the limitations imposed by the OS, they can provide jitter-free constant-lag stimulation. But who can say they are wild about the focusing and zooming issues related to rear projection? I'm not... Also, really, 16.67 ms could be called a bit archaic, couldn't it? Screens using LED's as the light source are not an option, as already discussed (we should call them LCDs, because that's what they are). However, OLEDs are a different matter (http://en.wikipedia.org/wiki/OLED). They require very little power/current, have excellent contrast and will (in principle) refresh at very high rates.

This might be a little off-thread, but I'd be keen to learn if anyone has had the opportunity to test an OLED screen, either in an MEG or MRI setting?

Best,

Chris
--
Christopher Bailey, MSc
MEG Engineer, MINDLab Core Experimental Facility
Center of Functionally Integrative Neuroscience (CFIN)
Aarhus University, Denmark

tel. cell: +45-2674-9927
tel. office: +45-7846-9944

On Nov 14, 2012, at 8:05 PM, Tom Holroyd (NIH/NIMH) [E] wrote:

That may not have anything to do with the projector. The software driver is simply waiting for the next vertical retrace interval before sending the data. Even though vertical retrace is an "archaic" concept originally necessary for CRT displays (you had to wait for the electron beam to sweep back to the top of the display), all cards provide this signal for compatibility. If you have a relatively modern video card you can probably get around this by disabling the vertical retrace in the driver configuration.

Our DLP/DVI system is similar. It has a rise time of about 5 ms and practically no jitter, but the software always waits for the next "retrace". It's usually no problem because it's consistent.

Maarten van-Casteren wrote:
Actually, one of the main problems with our current projector
is the lag: it only shows the input with a delay of two frames,
which at 60Hz is about 34ms. We would want something that
is a bit faster. A higher frame rate would also be nice, but the
main thing is the input lag.
Maarten
-----Original Message-----
From: Discussion list for international MEG community [mailto:[log in to unmask]] On Behalf Of Tom Holroyd (NIH/NIMH) [E]
Sent: 14 November 2012 17:45
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [megcommunity] LCD screen in MEG chamber
We use this Panasonic projector. It goes up to 85 Hz, though we usually run it at 60 Hz.
It works well.
http://www.projectorcentral.com/Panasonic-PT-D3500U.htm
You need to buy a non-standard lens to project onto a small screen at a short distance properly, see the "throw distance" calculator:
http://www.projectorcentral.com/Panasonic-PT-D3500U-projection-calculator-pro.htm
Beth wrote:
We are hoping to accomplish the same thing here in our MEG.  We would like to have refresh rates >75Hz with visual stims sent from Matlab using the Psychtoolbox.  This is quite difficult with the standard LCD monitor and our LCD projector.  Does anyone have a setup for refresh rates of 85Hz?  What type of DLP monitors are being used successfully for MEG vision studies?

Beth

--
The white knight is talking backwards.

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