New research from the Netherlands explores a placebo effect around high-definition TV. Of course, HD does look sharper, but the mind apparently can easily be tricked into thinking that regular TV is HD. From New Scientist (Wikimedia Commons image):
Sixty people in turn were shown the same video clip on the same television. Half were told to expect clearer, sharper pictures thanks to HD technology: an impression backed up by posters, flyers and the presence of an extra-thick cable connected to the screen. The other half were told to expect a normal DVD image.Think yourself a better picture
Questionnaires revealed that the people who had been led to expect HD reported seeing higher-quality images. "Participants were unable to discriminate properly between digital and high-definition signals," says Lidwien van de Wijngaert at the University of Twente in Enschede, the Netherlands, who carried out the study with colleagues from Utrecht University...
The results of the experiment might have been different had it taken place in North America, though, where conventional television uses the NTSC instead of the PAL technical standard. Picture quality is lower with NTSC, "so the difference compared with HD is much larger than for Europeans", says van de Wijngaert.