<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
font-size:11.0pt;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
span.EmailStyle19
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:70.85pt 70.85pt 70.85pt 70.85pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal>*Crossposting my response from cvnet in case folks are interested:<br><br>Hello Rufin,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>As a vision scientist working with display technology, I thought I could offer some insight into the problem you're experiencing. It is most likely caused by a hardware property of the specific LCD panels you tested. Since it may be relevant to others using high-frequency stimuli, I thought I would post my response here.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The liquid crystals in an LCD display are twisted and untwisted by a variable DC voltage. The degree of twist determines how much light passes through the screen to the viewer. The twists can be clockwise or counterclockwise.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Repeated twisting of liquid crystal in the same direction can, over time, cause the crystal's shape to become rigid or “stuck.” A consequence of this is a persistent afterimage like the one you describe, something like old-time CRT phosphor burn-in, as the pixel slowly returns to its normal state. Stuck pixels can also appear as dynamic flickering images.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Most LCD panels avoid “sticking” pixels by alternating the polarity of the DC current on even-odd frames of the display. This causes the twist to alternate between clockwise and counterclockwise. So if you have a white pixel driven by +5V, it is actually alternating between +5V on one frame and -5V on the next. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This means if you are flickering a 120 Hz screen at 60 Hz (white -> black -> white) then your stimulus is synchronized to the alternating voltage (+5V -> 0V -> +5V) and you are always twisting the liquid crystal in the same direction. This can cause your pixels to stick.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Depending on the manufacturer, some LCD panels may balance the voltage every two frames instead of every other frame; this is especially useful for 3D displays where frames alternate between left and right eyes. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I'm not sure what refresh rate you are running at, but I would bet that your 30 Hz stimulus has synchronized with your display's voltage balancing, whether it be even-odd frame (60 Hz refresh) or 2-frame alternation (120 Hz refresh) voltage balancing.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>You should be able to fix this by switching your display settings/refresh rate, or using an LCD with another voltage balancing strategy that doesn't synchronize with your stimulus.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hope this helps,<o:p></o:p></p><p class=MsoNormal>Lindsey<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Dr. Lindsey Fraser<o:p></o:p></p><p class=MsoNormal>Staff Scientist,<o:p></o:p></p><p class=MsoNormal>VPixx Technologies<br><br><o:p></o:p></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='mso-fareast-language:EN-CA'>From:</span></b><span lang=EN-US style='mso-fareast-language:EN-CA'> visionlist <</span><a href="mailto:visionlist-bounces@visionscience.com"><span lang=EN-US style='mso-fareast-language:EN-CA'>visionlist-bounces@visionscience.com</span></a><span lang=EN-US style='mso-fareast-language:EN-CA'>> <b>On Behalf Of </b>Rufin Vogels<br><b>Sent:</b> November 9, 2020 10:58 AM<br><b>To:</b> </span><a href="mailto:visionlist@visionscience.com"><span lang=EN-US style='mso-fareast-language:EN-CA'>visionlist@visionscience.com</span></a><span lang=EN-US style='mso-fareast-language:EN-CA'><br><b>Subject:</b> [visionlist] LCD / OLED monitors for vision science<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US>Hi, we are still using CRTs for stimulus presentation but want to switch to more modern technology. We have been testing some LCD displays (LG 27GN750 UltraGear (IPS panel) & iiyama G-Master Red Eagle GB2760QSU-B1 (TN) panel)) recently but when tested with an alternating black-white square ( e.g. at 30 Hz for several seconds) all show a dim flickering “afterimage” (physically present and measurable!) at the stimulated location for up to a minute. Does anyone know LCD (or OLED) monitors that have decent performance (for motion stimuli) and do not show such disturbing effects? <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Rufin<o:p></o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-CA'><img border=0 width=1 height=1 style='width:.0104in;height:.0104in' id="_x0000_i1025" src="https://mandrillapp.com/track/open.php?u=30884370&id=6393c8d458544b6eb7877cdd3fe0e1eb"></span><span style='mso-fareast-language:EN-CA'><o:p></o:p></span></p></div><img src="https://mandrillapp.com/track/open.php?u=30884370&id=ee95a67d40064d2ab7fcab5a3c8ab758" height="1" width="1"></body></html>