[Phys-L] Re: Reaction Time (was Re: Human Error?)

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

George wrote:

> Typical reaction times are on the order of .25 s; the stopwatches we use
> display precision on the order of +/- 5 ms.  I suggest to my students
> that claiming the instrumental limit as the uncertainty of their
> measurement is unreasonable, especially for a single trial.  Repeated
> trials characteristically show a standard deviation consistent with
> reaction time, rather than the stopwatch's displayed precision.

That's not at all what I find.  In my experience, good technique with
a stopwatch of sufficient instrumental precision easily results in
measurement uncertainties (derived properly from repeated
measurements) that are far smaller than typical reaction times.  For
instance, I can readily obtain a series of measurements for a ball
rolling down an inclined plane that has a standard deviation less
than 50 ms.

Moreover, even if the two were more consistent, I would argue
strongly that the uncertainty in such timing measurements--where
nothing is taking anyone by surprise--has essentially nothing to do
with the phenomenon that is properly called "reaction time."

John Mallinckrodt
Cal Poly Pomona
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