[visionlist] CRT vs. LCD

[Theo Veenker]

Peter Squire wrote:
> I am currently running behavioral testing with E-Prime
> software. I am displaying a probe stimuli near the edge of
> the screen for 30 msec. I have piloted the task on a LCD and
> CRT monitor. The CRT monitor appears to display the image
> fine, however, the LCD monitor does not appear to be
> presenting the image or is only displaying a partially
> image. Does any one have any ideas/papers/tech man. that I
> could check out for a reason why this is occuring. 

For the why part check out wikipedia and the many other resources about the
differences between CRT and LCD technology. I guess the response time of
your LCD is relatively long compared to the 30ms. BTW what refresh rate
enables you to get this 30ms number? At 100Hz three frames will give you
30ms, but I assume LCD can't do that. At 60Hz you can get 33ms.

In short, a CRT display (for computer/tv) is fast (electron beam hits fluorecent
screen, the phosphors emit light), an LCD display is slow (as it involves changing
alignment of crystal molecules). The important factors here are the response time
and input lag. There is a difference between black-to-black response time and
gray-to-gray response time. I understand the latter tends to be slower, although
some say the opposite is true. I suppose it depend on whether some sort of
overdrive/overshoot technique can be used to speed up the transition of the
crystals. Anyway marketing dictates that vendors will mention the fastest response
times whether btb or gtg. So in reality the numbers will probably be worse than
reported. Input lag is something you don't want. On wikipedia I read it can introduce
a delay of several frames. Also the contrast ratio of an LCD monitor is usually
not that good. So LCD's because of their poor specs, although they are getting
better, can't yet be used as drop-in replacement for CRTs.

While I'm here allow me to ask about CRT replacements. In our lab (mostly
experimental psycholinguistics, no vision research) we have CRTs everywhere, but
what to do once we can't buy CRTs anymore? I would love to see an LCD selection
sheet listing the minimal specs required for particular experimental purposes.
Or a list of recommended LCD (or plasma) monitors.

Theo