{"id":40252,"date":"2020-01-03T14:48:13","date_gmt":"2020-01-03T14:48:13","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40252"},"modified":"2020-01-03T14:56:01","modified_gmt":"2020-01-03T14:56:01","slug":"how-do-we-see-things","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40252","title":{"rendered":"How do we see things?"},"content":{"rendered":"<p id=\"top\" \/>\n<h3 class=\"wp-block-heading\">A thing is coherent stuff at a human scale<\/h3>\n\n\n\n<p>From the set of potential shape cues a substance can yield at a given scale, only a subset is effectively available at any given time; however, even after prolonged scrutiny, not all potential cues can be made effective. Fortunately, the succession of effectively revealed shape cues is most often coherent, which is sufficient for us to see a THING.<\/p>\n\n\n\n<p><em>Example<\/em>: a stone reveals its back face as we progressively turn it around, while the common parts (e.g., to front and side views) retain a coherent appearance.<\/p>\n\n\n\n<p><em>Counter-example<\/em>: the water surface of a river continuously changes shape; some patterns of waves remain coherent for a while, but can easily break off or be traversed by other patterns.<\/p>\n\n\n\n<p>A thing thus requires some amount of shape coherence: a wave is not a permanent thing, a stone is on a human time frame. These two examples are related to the concepts of slow and fast shapes of Koenderink. <\/p>\n\n\n\n<h3 class=\"wp-block-heading\">A God&#8217;s eye view?<\/h3>\n\n\n\n<p>Is there any veridical (god&#8217;s eye view) notion of a shape? For sure, one always needs to pick a scale, so no. However, if we agree on a specific scale dependence, nothing prevent us from defining a veridical shape: this is what 3D artists do in Computer Graphics software.<\/p>\n\n\n\n<p>Next: are we able to see the &#8220;veridical&#8221; shape of a thing at a human scale? Each sensory modality potentially gives access to a variety of shape cues about the object\/thing, but even if we consider all modalities, can we consider that all measurable aspects of an object shape are perceivable in a reasonable amount of time?<\/p>\n\n\n\n<p>Apart from the (inescapable?) missing of some shape details, is it possible that we things the way they are not? Magic tricks come to mind: an object is substituted for another without the audience noticing; hence the perception of a <em>coherent<\/em> set of cues is sufficient to give the illusion of object identity.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Shape illusions<\/h3>\n\n\n\n<p>Such an illusion commonly occurs in animation. In stop motion, different versions of a character part (e.g., its head) are prepared and interchanged at different frames; yet we perceive a coherent object identity. <\/p>\n\n\n\n<p>It goes even further with drawn animation, where each single frame is a different drawing, yet with sufficient coherence the sequence appears to depict a single object in motion.<\/p>\n\n\n\n<p>What makes coherence &#8220;work&#8221;? One way to know is to try to break it. Surprisingly, perfectly coherent 2D animations might not convey a coherent 3D object; but rather a collection of moving 2D shapes in the plane. <\/p>\n\n\n\n<p>Coherence might also be broken by multiple superimposed unrelated motions; how does this differ from a coherent transparent object? Here the presence of contours tying together different transparent layers is likely to be key&#8230;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A thing is coherent stuff at a human scale From the set of potential shape cues a substance can yield at a given scale, only a subset is effectively available at any given time; however, even after prolonged scrutiny, not all potential cues can be made effective. Fortunately, the succession of effectively revealed shape cues &#8230; <a title=\"How do we see things?\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40252\" aria-label=\"Read more about How do we see things?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[651],"tags":[],"class_list":["post-40252","post","type-post","status-publish","format-standard","hentry","category-thoughts"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40252","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=40252"}],"version-history":[{"count":2,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40252\/revisions"}],"predecessor-version":[{"id":40254,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40252\/revisions\/40254"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40252"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40252"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40252"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}