[Sorry, I did'n know this system does not support punctuation marks
supported by word processors. Repost.]

David,

I was too laconic in my previous message and did not explain what
meaning of "interference" was used.

Webpage scrolling is an automatic activity involving perceptual and
motor skills working in concert. This automatic activity is
unconscious and effective. A portion of user's cognitive load
allocated to scrolling is very low. In other words, the user do not
"think" about how to scroll a page, he simply scrolls it, and it
scrolls.

When you place second scrolling mechanism (slider) on a webpage, you
introduce a dissonance into automatic scrolling activity. Now for the
same task -- scrolling -- there are two modes of operation: one for
the scrollbar, another for the slider. (Slider cannot be operated by
a mouse wheel; it is not clear how to scroll down exactly by one page
etc.) As a result, a user is faced with two different scrolling
controls and his automatic skill became damaged. Unconscious became
conscious: the user starts thinking about how to act in each case.

This is what I meant by "interference", a cognitive interference.

Then, imagine a realistic situation when at the current moment of
page scrolling only a half of the slider is visible on screen while
its another part is hidden below the bottom edge of the browser
window. This is a real dilemma for a user: which of two scrolling
mechanisms to use: scrollbar or slider?

Finally, I do not think the concrete example of a slider you
mentioned in your initial message is very different visually from a
scrollbar. Mentally rotate that slider by 90 degree right and imagine
that current webpage is long and therefore its scrollbox is small: in
this case a slider and a scrollbar will look as twins...


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Posted from the new ixda.org
http://www.ixda.org/discuss?post=42001


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