Fog illusion

posted in: Other news, Outreach | 0

Recently, science journalist Karel Knip of Dutch newspaper NRC handelsblad asked Frans Cornelissen the question of whether objects could appear larger in fog or at dusk than they really are. In his column he cites some sources that had claimed this observation. While Frans had never heard of a “fog illusion”, he decided to look into this a little. Following some consultation with colleague Eli Brenner of VU (who suggested “aerial perspective” which lowers contrast (read more about this in this book chapter) and might result in errors of distance judgement, and blur, could contribute perhaps to this. To visualize the phenomenon, Frans created a toy simulation (see below).

The illusion is not overwhelmingly large, but it seems to “work”, in particular when viewing this on a fairly large screen, from a distance (say ~ 2-3 m) and with only one eye (to eliminate stereo-cues). Note that the only difference between the images below is a substantial drop in contrast in the lower one. Individual differences will certainly affect the strength by which you will experience any illusory size difference. A pdf with some more examples can be found here. In some examples, the effect appears to be stronger. Judging from the below example, one factor might be a flattening of the perspective, resulting in wrongly judging distance. And apparently, human observers tend to overestimate distance and consequently size.

Why a dear is used in the example: when Knip first posed the question, Frans was visited by a hunter from the US, and when asked whether he had ever experienced this, he mentioned the anecdote that quite a few hunter colleagues had stories about dear that initially looked enormous, but upon later inspection turned out to be fairly normal in size. And the case is, hunting often takes place at dusk or dawn……..