I was thinking you meant Instrument basics. I'll admit that there were times when I would turn off the PFD to force a primary student to look outside. I'll also say that I've had the same thing happen with steam gauges. Its fairly common for a student to fixate on whatever instruments there happen to be. Its up to the CFI to ensure that they do not. I think the phenomemnon you're describing is more attributable to lack of experience and proper instruction than the equipment.