[visionlist] CRT vs. LCD

[Michael Bach]

Dear Peter + all:

> 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.


What you are seeing is temporal aliasing. Briefly soapboxing: "Limits  
of CRTs in Vision Research"
<http://www.uniklinik-freiburg.de/augenklinik/live/homede/mit/bach/ops/crtlimits_en.html 
 >
should now be complemented by "Limits of LCDs in Vision Research".

The topic has already been touched upon on this list in some earlier  
posts. The problem with CRTs is that they (typically) have an internal  
frame buffer, which is read out (copied to the screen storage  
transitors) at 60 Hz. What you are feeding in, be it via VGA  
connection (analog) or DVI (digital) refreshes said buffer at whatever  
rate you are driving it. Only sorry results can result, if you are  
changing the screen content every 30 ms or so.
This is a very problematic state of affairs, especially for people  
doing evoked potential stuff where you care about single milliseconds  
in response to visual change -- BOLD responders couldn't care less.

If anyone would come up with a solution, that would be really great! I  
have just bought another good CRT monitor for the shelf...


Best, Michael.
-- 
Prof. Michael Bach PhD, Ophthalmology, University of Freiburg,  
Killianstr. 5, 79106 Freiburg, Germany.
President of ISCEV <http://www.iscev.org/>
Visual illusions:  <http://www.michaelbach.de/ot/>