Your calamari wants a flat screen

Octopuses and their relatives are just incredible animals.  Not only do they manage to coordinate hundreds of suckers on 8 arms simultaneously without tripping over themselves (I can't even remember what I ate for breakfast) and have the most advanced eyes in the invertebrate world, but they can do other cool stuff like eat sharks,  fit through holes much smaller than themselves, use tools and learn from each other.  Now a new study has shown that they can tell the difference between regular TV and HD.  How did they determine this?  Simply, as it turns out.  The octopus show no reaction to footage of other octopus or crabs shown to them on regular TV screens.  When shown real crabs or crab footage in hi-def, however, the octopus lunged as if to attack the hapless decapod (video link).  In other words, octopus can tell the difference between real and imagery, if the image is not of high enough quality.

The explanation appears to lie not in the resolution of the screen (how small the pixels are) so much as how fast the picture can be draw and redrawn on the screen.  The picture on a TV screen is constantly being created line-by-line from the top of the screen in a process called rastering.  We don't perceive this rastering because it happens faster than we can see; faster than our "critical flicker frequency".  Well, not everyone has the same critical flicker frequency, and nor do all televisions have the same rastering rate.  Most hi-def TV's have a higher frequency (120 or even 240Hz, or times-per-second).  It may be that low-def TV is below the octopus critical flicker, but hi-def is above it.  In this way, they would see a sort of strobing effect in normal footage, but the hi-def stuff would look like, well, a crab.

The authors also noticed that the octopus showed "episodic personality", which is to say they were interested in the crab (or footage of another octopus) some times but not others.  I'm not sure I would class that as evidence of personality, just a less-than-100%-predictable response to a stimulus.  Having said that, ocotpus do have obvious personalities, which is one reason people are so drawn to them.  That, and sweet chilli sauce...

Pronk, R., Wilson, D., & Harcourt, R. (2010). Video playback demonstrates episodic personality in the gloomy octopus Journal of Experimental Biology, 213 (7), 1035-1041 DOI: 10.1242/jeb.040675