Crazy observation on Ragestache Comics

[svrphy]

I just found this weird observation in Ragestache Comics. Anybody care to explain to me why one can Retain the troll face even after sometime ?? (Eg. I could Retain the figure in my mind for more than 4.5 mins ).http://cdn.ragestache.com/2012/1/23/ragestache.com_30398_1329012006.jpg [Broken] BTW, could this idea be used to memorise things better ??

 

[Evo]

This happens anytime you look at a light or dark image then look away, nothing to do with this comic.

Negative afterimages are caused when the eye's photoreceptors, primarily those known as cone cells, adapt from the overstimulation and lose sensitivity.

http://en.wikipedia.org/wiki/Afterimage

 

[Enigman]

A few more afterimages:
http://www.optical-illusionist.com/category/afterimages/