Above the 75th percentile
Switch cost is a difference, not a time: the mean response on trials where the rule changed, minus the mean on trials where it stayed. So the scale does not reward a fast hand — overall speed subtracts itself out. A surcharge of thirty to a hundred and fifty milliseconds means you were applying the new rule in time rather than remembering it after already answering by the old one. What it does not mean is an ability to do two things at once. Switching is precisely the absence of simultaneity — you are always working under one rule, and the only question is what the change costs. The feeling of being easily derailed is measured by a different scale: attention drift, in the impulsivity test, which is self-report rather than milliseconds.
Middle: 25–75
A surcharge of one hundred and fifty to three hundred and fifty milliseconds is the ordinary price of a rule change, and everyone pays it: it is never zero. Most of it arrives on the first trial after the switch. The old rule does not turn off on command — it keeps competing with the new one for a while, and it is on that trial that the hand reaches to sort by colour when the question is about shape. Later in the block the cost falls. The practical reading is narrow: in this zone the surcharge is moved not by attention training but by whether you read the switch cue before the figure appeared.
Below the 25th percentile
A surcharge of four to five hundred milliseconds and up is a high price for a change, and here more than on the other scales it matters what it is made of. There are only fifteen trials and the switches are the smaller share of them, so a single thoughtful trial moves the difference visibly: this is the noisiest scale in the battery. Second: if you missed the switch cue, the first answers after it went by the old rule — and that reads as a high cost even though no switching happened at all. The number does not describe multitasking ability and has no clinical meaning. The feeling of switching easily is a separate scale: attention drift, in the impulsivity test.