John Conway
&gt; I also recall Conway spending several weeks trying to construct a strange periscope-type device to try to help him visualize four-dimensional objects by giving his eyes vertical parallax in addition to the usual horizontal parallax, although he later told me that the only thing the device made him experience was a headache.<p>I&#x27;m quite curious what exactly Conway was trying to do here.  The parallax we use for depth sensing is indeed horizontal in terms of the axes of the image we see, because our two eyes are separated horizontally.  With a periscope you might be able to simulate two eyes separated diagonally or vertically.  But how does that help you visualize four-dimensional objects?