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<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US">Hi Arun,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US">Thank you for sharing this. Have you considered whether this might reflect there is a non-linear relationship between your nominal intensity steps and the change in luminance on the
monitor? If the function is an accelerating one (like a gamma function), the incremental luminance steps from your darker background will actually be a bit smaller than those from the brighter background, even though the change in pixel values are identical.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US">Kind regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US">Andrew <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">Assoc. Prof. Andrew Anderson<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">Department of Optometry & Vision Sciences<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">The University of Melbourne, 3010<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">AUSTRALIA<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">Ph: (+613) 9035 9916</span><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">visionlist <visionlist-bounces@visionscience.com> on behalf of SP Arun <sparun@iisc.ac.in><br>
<b>Date: </b>Thursday, 25 August 2022 at 3:32 am<br>
<b>To: </b>"visionlist@visionscience.com" <visionlist@visionscience.com><br>
<b>Cc: </b>Thomas Cherian <thomasc@iisc.ac.in><br>
<b>Subject: </b>[visionlist] brightness change detection puzzle<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span class="xelementtoproof"><span style="font-family:"Arial",sans-serif;color:black;background:white">Dear visionlist, </span></span><span style="font-family:"Arial",sans-serif;color:black">
<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">We have a brightness perception puzzle in the image linked below. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span class="xxelementtoproof"><span style="font-family:"Arial",sans-serif;color:black"><a href="https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing">https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing</a></span></span><span style="font-family:"Arial",sans-serif;color:black">
<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">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, whereas for brighter backgrounds, we found that much smaller brightness changes could be detected. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">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. <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">All this must be because of contrast detection somehow. But we are unable to think of reasons why this is happening. Any ideas? <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Regards, <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Arun<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">---<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">SP Arun<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Professor <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Centre for Neuroscience<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Indian Institute of Science<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">Bangalore 560012<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">T: +91 80 22933436 <o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-family:"Arial",sans-serif;color:black">W: <a href="https://sites.google.com/site/visionlabiisc" title="https://sites.google.com/site/visionlabiisc">https://sites.google.com/site/visionlabiisc</a><o:p></o:p></span></p>
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