[email protected] (Carl Fogel) writes:
> Tim McNamara <
[email protected]> wrote in message news:<m265dirnx1.fsf@Stella-
> Blue.local>...
>
> > Well, you had some perceptual learning that the average
> > customer wouldn't have had, which should make you a
> > little more sensitive. However, picking up a bike and
> > judging which is lighter is a matter of perceptible
> > differences (there is a limit called "least perceptible
> > difference" below which people cannot reliably perceive
> > the difference). Most people could probably be accurate
> > as to which is lighter within a pound or so.
>
> I'm not sure whether "least perceptible difference" is a
> subtly different notion than the common "just noticeable
> difference."
Close enough.
> One problem here is that comparing bicycles is different
> than the usual psychology class experiment. A different
> range is involved.
Well, there are lots of differences including range of
weights involved as well as various other potential
confounds. However, the fundamental idea is the same as in
your examples below.
> In psychology classes, students get about ten seconds to
> pick up two small weights (around 100 grams). They can
> pick up both at once, switch them from hand to hand, and
> do anything they please to compare them. One weight is
> increased, usually a gram at a time, until students can
> finally notice a difference.
There have been many, many variations on this type of thing;
of course, I am also thinking about critical literature as
well as common classroom illustrations of the principles
involved. Not only weights, but electrical stimulus,
pinpricks, temperature, etc. Any college textbook on
perception would cover this information adequately for the
purposes of our discussion. I would suggest, however, that
if you're interested in this topic, James J. Gibson's _The
Senses Considered as Perceptual Systems_ (1966) and, to a
lesser extent the somewhat misleadingly titled _The
Ecological Approach to Visual Perception_ are gold mines of
information; the work of Eleanor J. Gibson (who created the
field of perceptual learning) and Anne D. Pick is also very
illuminating.
> But it's not very good (and you have to go all the way
> through it to find the right table). It would be wonderful
> if you have any links to better JND data. I really don't
> know of any tests for the JND for twenty-pound objects.
Heh! That's because the average psych lab doesn't have a
convenient set of 20 lb weights handy. There is a
mathematical relationship between the mass and the
differences between masses in terms of what is perceptible.
You're more likely to be able to discern the difference
between a 10 and 20 gram pair of weights than between a 200
and 210 gram pair.
What the Gibsons (and others) demonstrated is that
perception of differences becomes more accurate with
practice in all of the sensory systems- perception is fairly
self-educating. Someone posted about having built 8,000
pairs of wheels and being able to tell by touch and sound
whether the wheel is adequately tensioned. I don't have too
much trouble believing that because this is someone who's
had a lot of perceptual learning over time. I doubt he could
tell you what the tension *is* (e.g., squeezing a pair of
spokes or plucking a spoke and telling you "106 kgf" or
"1024N") but his range of perceptible differences is likely
to be more finely calibrated than mine having built just
several hundred wheels. The nature of haptic (motor-sensory)
perception being what it is, I'd probably be able to tell
you if a wheel is undertensioned more accurately than if
it's overtensioned by squeezing because of the larger range
of motion and the increasing tension in the spokes as they
are squeezed together.
> (Baseball umpires occasionally test major league pitchers
> by saving rejected balls and offering them again an inning
> later. They report that the pitchers routinely reject the
> balls again, indicating that for a million dollars a year
> some people can distinguish tiny differences in 5-ounce
> objects.)
You'd probably be able to find minor league pitchers capable
of the same discernment. It's not the paycheck but the
perceptual learning that's the key. These folks handle more
baseballs than we do and hence their range of perceptible
difference is finer.
> The other problem is the test effect. What we can notice
> when deliberately trying to tell the difference between
> two weights on a test is probably a smaller difference
> than what we notice when we're unaware that there might be
> a change and are getting on our bikes and riding off.
Yes, whether you are paying attention makes a difference.
If you are not, then the difference has to be significant
enough to intrude into awareness. That's why differences
that develop gradually are harder to notice- they are less
likely to announce themselves to our awareness than an
acute change.
> One test would be whether people notice the difference
> between an empty water bottle and a full one, but then
> they know that there should be a difference.
But if they don't know, I'd highly doubt they could reliably
be accurate. It's a small difference in a complex dynamic
system. And that's a fair amount of weight, given that water
weighs 8 lbs to the gallon; a full 20 oz water bottle should
weigh about 1.25 lbs. People rarely complain about the
weight of their bidons, yet claim they can feel a 6 ounce
difference in frame weight.
> So here's a more entertaining test. How large a lead
> weight can you sneak into the bottom of someone else's
> tool bag before they catch on?
>
> I think that your post suggests a pound or so, which seems
> plausible, but I'd love to know of any formal studies or
> wicked private tests---half a pound, a full pound, two
> pounds, three, four, or even five?
I think it'd be more weight than that. Picking up a bike is
one thing, there are many sources of information about its
weight through the hands, arms, shoulders, neck and back.
These parts of the body are finely attuned to judging
weight. Riding a bike is different, because it's supporting
your weight rather than you supporting its weight. IMHO it
would be much harder to make this discernment from riding
compared to hoisting the bike in your hands.
