Why would one need a study for this? It's obvious. I always have to look at the touchscreen to press a button on it, not so for buttons. The touchscreen doesn't always "take" it, either, and I have to try several times.
It's a large difference in time.
Properly designed buttons should also have various shapes and textures so your fingers learn which ones are which by feel. Airplanes do this - for example, the knob to lower the landing gear is a little tire. The knob to lower the flaps has a knob shaped like a wing on it.
I come from the aircraft industry where this is a big deal, but the auto people go for a "cool" look rather than a "safe and reliable" look.
With haptic feedback you could even receive morse with nobody the wiser.
There is a very real problem in the sciences that doing "unsexy" science is treated a waste of time.
For example, the fuel icon is a picture of a fuel pump with an arrow on one side of it, say on the right side pointing to the right.
Does this mean:
1. The fuel pump goes on the left side of the car and one inserts the pump to the right
2. The fuel pump goes on the right side of the car and one inserts the pump to the left
Both are quite reasonable interpretations. I always have to stop and think which one it is. If it said "cap on right" then there's no ambiguity.