the loch ness monster bias
We're familiar with the idea that none of us 'thinks as much as we think we think'.
It would also appear that we don't even see as much as we think we see.
Our thanks to Faris, who posted this Transport for London info spot from 2008 that demonstrates the idea of 'change blindness'.
'Change blindness' one of those little cognitive traps that shows the inherent flaws in how we process visual information.
'Whodunnit' is clearly a close relative of this 1998 study by Daniel Simons and Daniel Levin called 'The Door Study' in which a participant fails to notice when the person he is talking to is replaced by someone else, clearly demonstrating the phenomenon.
There's a full academic paper available; 'Change Blindness Blindness: The Metacognitive Error of Overestimating Change-detection Ability' if you are inclined to read more.
I'm reminded of what we doctors call 'The Loch Ness Monster bias'.
Roughly translated this means that rather than rather than using the maxim 'I'll believe it when I see it' we would be better advised to note that we will, 'see it when we believe it'.