In general, your visual response time is about 200 ms. Anything below that is fine for regular visual feedback such as highlighting a button after it has been p

In general, your visual response time is about 200 ms. Anything below that is fine for regular visual feedback such as highlighting a button after it has been pressed. This is due to latency in the processing of visual information in the brain. Touch screens are somewhat unique however in that they track physical movement directly. This means that they do not only have to compete with the latencies in the visual system, but also with the predictions of physical movement that we do. Even though we can percieve visual information only at a 200 ms delay, our predictions of the physical world are compensated for that. Thus, even small latencies are percievable. I think Microsoft did some research on this and they concluded that even single-millisecond delays in touch screen tracking were noticeable. They even claimed that sub-millisecond delays felt "completely different" and much more real.