Wednesday, 3 September 2014

And still it moves

Moving stillI saw a photo on a wall recently and one small bit of the picture was continually moving. I assumed it was a flat video screen of the type that commonly hangs on walls these days. I was disconcerted to discover, on closer examination, that it was actually a still photo mounted on board! And yet, a small part of the picture continued to move. An anomaly indeed! How was it possible?

There are, of course, examples of static pictures that appear to move (see here, for instance). However, such pictures usually consist of highly artificial patterns. But is it possible to see motion in still photos of natural subjects? If so, it might be possible to see anomalous movement in static objects in every day life.

To investigate, I tried to reproduce the photo I saw. It consisted of a word, in large type, photographed using what photographers call the 'zoom effect'. The bit that 'moved' was a single letter. The zoom effect looks as though the camera is moving towards, or away from, the subject during the exposure. I reproduced this effect using the front page of the latest issue of ASSAP's own Seriously Strange magazine, for its large headlines. I took lots of photos and most showed nothing odd.

Moving still with pointerHowever, a couple of photos DID show a faint hint of apparent movement. Of course, it may just be me, perhaps because I often notice misperception. But maybe some other people might see it too (particularly others who notice misperception). The best example is shown above. You will see some zoomed words too blurred to be read easily. However, there is a white trapezoid area (indicated by the arrow in the second version of the photo - right) which appears to move. Specifically, the nearest edge looks as though it is continually advancing and retreating. At least, it does to me. I'd be interested to hear from anyone who can see this apparent movement.

The apparent motion in artificial patterns has been explained as a result of microsaccades (see here). That may be the explanation here too, but I'm not so sure. I wonder if this one is more a brain thing than an eye thing. The reason I say that is because the zoom effect gives the visual appearance of movement. It might be deceiving the watching brain into seeing illusory movement in certain specific circumstances in the same way that pictorial perspective can sometimes mislead. I only found this effect in a tiny number of similar photos, so it probably only occurs for very specific circumstances.

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