<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);" class="elementToProof">
<span class="x_elementToProof" style="font-size:11pt;margin:0px;background-color:rgb(255, 255, 255)"><span style="margin:0px">Dear visionlist, </span></span>
<div dir="ltr" class="x_elementToProof" style="font-size:14px;font-family:"Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif;margin:0px;background-color:rgb(255, 255, 255)">
<div class="x_x_elementToProof x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<br>
</div>
<div class="x_x_elementToProof x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
We have a brightness perception puzzle in the image linked below. </div>
<div class="x_x_elementToProof x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<span class="x_x_elementToProof" style="margin:0px"><a href="https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing" data-auth="NotApplicable" style="margin:0px">https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing</a></span>
<div style="margin:0px"><span class="x_x_elementToProof" style="margin:0px"></span></div>
<br>
</div>
<div class="x_x_elementToProof x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
When we tried to find the smallest change in brightness detectable against a uniform background, we found something strange: for dark backgrounds, we found that only large brightness changes could be detected<span style="margin:0px">, whereas for brighter backgrounds,
we found that much smaller brightness changes could </span><span style="margin:0px">be detected. </span></div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<br>
</div>
<div class="x_x_elementToProof x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
This was puzzling to us because this is the opposite of Weber's law -- by Weber's law we would expect that the threshold brightness change for brighter backgrounds should be larger than for darker backgrounds. But we observe the opposite. </div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<br>
</div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
All this must be because of contrast detection somehow. But we are unable to think of reasons why this is happening. Any ideas? </div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<br>
</div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
Regards, </div>
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
Arun</div>
<div style="margin:0px">
<div class="x_x_elementToProof" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<br>
</div>
<div style="margin:0px">
<div style="margin:0px">
<div style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px"></div>
<div style="margin:0px"></div>
<div dir="ltr" style="font-size:11pt;font-family:Arial, Helvetica, sans-serif;margin:0px">
<p style="margin-top:0px;margin-bottom:0px"></p>
<div style="margin:0px">---</div>
<div style="margin:0px">SP Arun</div>
<div style="margin:0px">Professor </div>
<div style="margin:0px">Centre for Neuroscience<br>
</div>
<div style="margin:0px">Indian Institute of Science</div>
<div style="margin:0px">Bangalore 560012</div>
<div style="margin:0px">T: +91 80 22933436 </div>
<div style="margin:0px">W:<span> </span><a href="https://sites.google.com/site/visionlabiisc" data-auth="NotApplicable" title="https://sites.google.com/site/visionlabiisc" style="margin:0px">https://sites.google.com/site/visionlabiisc</a></div>
<span style="margin:0px"></span></div>
</div>
</div>
</div>
</div>
<br class="Apple-interchange-newline">
<br>
</div>
<div dir="ltr">
<div dir="ltr" class="x_elementToProof">
<div>
<div>
<div>
<div dir="ltr" style="font-size:11pt; color:#000000; font-family:Arial,Helvetica,sans-serif" class="elementToProof">
<p style="margin-top: 0px; margin-bottom: 0px;margin-top:0px; margin-bottom:0px; margin-top:0px; margin-bottom:0px">
</p>
<p style="margin-top: 0px; margin-bottom: 0px;margin-top:0px; margin-bottom:0px; margin-top:0px; margin-bottom:0px">
</p>
</div>
</div>
</div>
</div>
</div>
</div>
</body>
</html>