Monday, 30 June 2014

change blindness

I went to a fascinating seminar by Professor Stephen Tipper last week.  It was about how perception (mostly vision described here) and action deeply influence each other.  There were lots of fascinating examples (with predictions backed up by clever experiments):
  • Moving your finger clockwise or anticlockwise can change the apparent rotational direction of some flashing spots.
  • Merely looking at a picture of a footballer v a tennis player activates your foot or hand mirror neurons respectively (although I personally didn’t even recognise the photos!).
  • Watching someone perform a movement fluently v more awkwardly can affect your emotional response to them positively or negatively respectively (does this mean my left-handed self shouldn’t write on a whiteboard in front of my predominantly right-handed students?).
One aspect that caught my attention was the illustration of change blindness: how quite large changes in a scene are completely invisible, until eventually seen, at which point they cannot be unseen.  One of the examples shown was "couple at dinner".

The version above is taken from a webpage on a talk by J. Kevin O’Regan  and Alva Noë.  It seems to be flashing slower than the example in the talk, and I can’t tell if it still works, because now that I know the change, I can’t unsee it!  However, that page has several other examples, which did all work for me.

After talks like this, I never want to trust anything I see again!  But what really caught my attention about the change blindness segment of the talk was a seeming contradiction between what I was witnessing here, and something I’ve experienced before.  A blink comparator is used in astronomy to  to detect planets and other rapidly moving bodies.  Two images of the night sky are switched back and forth, and any object moving against the essentially motionless stars leaps out to the viewer.  How can a blink comparator work if we suffer from change blindness?

I asked Stephen about this after his talk.  The answer: it’s all in the timing.  The blink comparator blinks faster than do the change blindness images.  Blinking fast enough engages our motion detectors; blinking slower does not, and we become change blind.



  1. It works well, I've spent a whole minute searching for it.

    1. But now you've seen it, it's really obvious, isn't it?