Whilst in the cage with my other half she started nutting off about drivers not indicating. For me, I hadn't noticed it for ages, so I started thinking why. I hadn't even noticed that the cages that hadn't used the indicators, instead I had already anticipated their move. Since then I have returned to my comfort zone (on the bike) I've noticed that in most cases a lane change or turn is quite obvious long before the indicator is used.
Part of my wondering lead me to looking at what we react to it seems that the flashing lights of an indicator are secondary compared to a minute movement of the drivers head or position on the road.
Change in colour:
http://www.happyhub.com/network/reflex/
Movement:
http://www.bbc.co.uk/science/humanbody/sleep/sheep/
Bookmarks