Top-Down and Bottom-Up Processes in Web Search Navigation

target category, bypassing link evaluation altogether. These
findings are consistent with the possibility that participants
generated their own category names through top-down
processing prior to carrying out the search process.
Given the equivalent and overall fast selections in the two
category-unambiguous conditions, it is reasonable to believe
that participants generated their own category names even in
the absence of them based on their knowledge of the
descriptions and the information architecture. In contrast,
use of a bottom-up strategy seems implausible for the faster
selection times (i.e. < 3 seconds). After accounting for page
refresh, mouse movement and link selection, little time
remains for an item-by-item evaluation of the category
labels, which must take at least 230 ms per link to account
for the time needed for each eye movement (Card, Moran,
& Newell, 1983).
The present findings also suggest that the presence of
category names facilitates category selection at least when
the search target does not have a clear category selection. In
these cases, the participants may still use the more efficient
top-down strategy, relying on the category name in the
description to perform the visual search for its physical
properties. Category ambiguity still incurs a greater time
cost, possibly to confirm category membership or consider
alternate categories before making the selection.
Not surprisingly, the trial number was a significant factor
for the amount of time used to select a link. In particular, the
selection time decreased with the number of trials. This
result is consistent with increased use of top-down strategies
as users become more familiar with the categories and their
location on the page.
The presence of efficient top-down strategies has
implications for the effective design of web pages and menu
systems. In applied web design usability research, the
superordinate category names are sometimes referred to as
“trigger words” to signify in a post-hoc manner their being a
user’s internally formulated search goal and triggering a
selection response from the user (Spool, Perfetti, & Brittan,
2004). To the extent that users form key “trigger words” and
then scan for their physical properties, care must be taken to
include these words in the selection labels. Otherwise, users
may miss the targeted selection even if its label is highly
relevant to the user’s information goal. This consideration is
consistent with Spool’s advice of identifying common
trigger words for users and including them in link labels.
Certainly any postulation of dichotomy is prone to
oversimplification. The question is whether making such a
distinction is useful in the understanding of different
mixture of processes that may go on in link-based search.
Although computational modeling in web search has seen
great improvements, empirical investigation of the issue in
our opinion is still lacking. The present research represents a
step in finding factors that elicit top-down processing and
measures that indicate when top-down processing occurs.
1853
Acknowledgments
This work was funded by grant NNA06CA99A from
NASA’s Human Research Program. We are indebted to Jim
Lofton who developed the "UI Nav Test" web application,
which we used to administer our navigation studies. We also
thank Paul Roth, Mike Niebling, Ben Burton, Nils Hanson,
Devin Carter and Anna Eskra for testing and commenting
on preliminary versions of the web application, Jaymie
Massoletti for assistance with data analysis, Usha
Viswanathan for participants recruit, and Joel Lachter for
equipment setup.
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