1. Challenging Information Foraging
Theory: Screen Reader Users are not
Always Driven by Information Scent
24th ACM Conference on Hypertext and Social Media
Hypertext 2013
Markel Vigo1 & Simon Harper2 University of Manchester (UK)
1: @markelvigo
2: @sharpic
markel.vigo@manchester.ac.uk
simon.harper@manchester.ac.uk
http://dx.doi.org/10.6084/m9.figshare.695073

2. Problem
• We do not know all the navigation
tactics employed by screen reader
users
• Key to build navigation models
• Lack of navigation models for screen
reader users
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3. Goal
• Bridge the gap on the lack of
knowledge on navigation tactics
• Survey existing navigation models (for
sighted user)
• Inform navigation models to make
robust models
• Consider coping strategies
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4. Navigation models
• High certainty about a constrained
universe
• Predict user behaviour
• Interaction models: GOMS, KLM
• Evaluation of interfaces
• Often used in research settings
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5. Navigation models
• Built on Information Foraging Theory (IFT)
– Web page ≈ information patch
– User ≈ consumer
• Link selection=
• Information scent (IS) measures the
relevance of proximal cues that lead
towards distal goals
ACM Hypertext 20132 May 2013
Max
E(Info_Value)
E(Cost)
é
ë
ê
ù
û
ú
5

6. Navigation models
• Models for sighted user differ on
– The conceptualisation of information scent
– On the strategy for page reading
• Few empirical studies are based on link
selection or navigation strategies
• Low predictive power
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7. Who are screen reader
users
• Blind users
• Low vision users
• Potentially generalisable to users of
auditory interfaces:
– Applications on the move: car, walking, cycling
– Situationally disabled users
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8. How do screen readers
navigate
• What do we know so far?
• Behaviours occurring on ideal situations
• How is the navigation when
encountering:
– Accessibility barriers
– Design issues
– Usability problems
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9. Stereotypical behaviours
ACM Hypertext 20132 May 2013
1. Miscellaneous top links
2. Mast header
4. Main content
5. Banner
3. Primary
navigation
links
6. 2ndary
navigation
links
7. Footer
8. Miscellaneous bottom links
1. Miscellaneous top links
2. Mast header
3. Primary navigation links
4. Main content
1. Miscellaneous top links
2. Mast header
3. Primary navigation links
4. Main content
(a) Listening to content (b) Exhaustive scanning
9

10. Stereotypical behaviours
ACM Hypertext 20132 May 2013
1. Miscellaneous top links
2. Mast header
4. Main content
5. Banner
3. Primary
navigation
links
6. 2ndary
navigation
links
7. Footer
8. Miscellaneous bottom links
H
1. Miscellaneous top links
2. Mast header
3. Primary navigation links
4. Main content
(d) Information scent driven gambling
scanning: headings navigation
H
H
H
H
H1. Miscellaneous top links
2. Mast header
3. Primary navigation links
4. Main content
(c) Gambling scanning: skip
line navigation
skip 6 lines
skip 5 lines
skip 5 lines
skip 5 lines
10

11. Analysis of coping tactics
• Secondary analysis of 2 user studies
– Ethnographic longitudinal
– User test
• 17 users
• Isolated 9 coping tactics grouped by
– Link selection tactics
– Exploration tactics
– Navigation tactics
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12. Link selection tactics
T1: Deliberately clicking on low
scented links
• Accessibility problems:
– “I'm just going to click on one of these
things, I don’t know what it is for ”
• Information overload:
– “when I was listening I heard the target
link... you can have 30 or 230 links that
you have to sit and listen to! ”
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13. Link selection tactics
T2: Clicking on any link
• When coming across unexpected
functionalities or content
– On a linked keyword search where search
box expected: “does not tell me where to
do this ”
– On a SERP that did not contain expected
results: “found a few links, none directly
what I want ”
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14. Intra-page exploration
tactics
T3: Escaping from useless or
inaccessible content by tabbing down
T4: Fast tab/arrow down the page
without completely listening to content
– By default
– On familiar pages
– On content arranged according to some
criterion
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15. Intra-page exploration
tactics
T5: Gaining orientation
• By going to the top of the page
– “not sure where I am...if in doubt go back
to the beginning ”
• Users pay more attention in the second
reading
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16. Inter-page navigation
tactics
T6: Backtracking to a shelter
• When user mobility is reduced
– Getting stuck: “I seem to have come to a
dead end here”
– Looping behaviours: “I’ve got back to
shorts again...shorts again!”
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17. Inter-page navigation
tactics
T7: Re-checking
• Fast revisitations as reassurance
mechanisms
T8: Retracing
• Users retrace their steps from a shelter
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18. Withdrawal
T9: Giving up
• Provoked by sequence of failures and
unsuccessful interactions.
• Observed on users who navigate with
trouble and encounter an obstacle
different to ones experienced.
• E.g.: encountering accessibility barriers
after escaping from a loop of pages
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19. Implications
Informing navigation models
• Navigation models for sighted users
mimic screen reader user behaviour in
ordinary circumstances
• To cover extraordinary circumstances
minor modifications are needed:
– Gaining orientation (T5)
– Re-tracing (T8)
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20. Implications
Challenging established conceptions
• In ordinary circumstances IS is a reliable
indicator
• In extraordinary circumstances users are
not driven by IS but escape from problems
– Click on low scented (t1) or any link (t2)
– Fast tabbing down (t3, t4)
– Backtracking to a shelter (t6)
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21. Implications
Challenging established conceptions
• IFT: a hyperlink will be selected when the tradeoff
between information gaining and cost of accessing
is low
• SR users: cost of accessing is minimised at the
expenses of gaining low quality information
• Alternatively, SR users have low satisficing levels:
any web patch is good enough
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Max
E(Info_Value)
E(Cost)
é
ë
ê
ù
û
ú

22. Implications
Challenging established conceptions
• This behaviour reminds of that of animals
making risk-sensitive foraging decisions
– Risk prone individuals: those undergoing
extreme situations take the risk of selecting low
scented link (t1,t2)
– Risk averse individuals: less severe problems
take a more conservative strategy by moving to
another web patch (t3, t4, t6)
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23. Implications
Challenging established conceptions
• IFT: users leave a website when the scent of the
current page is below the average of the pages
visited
• SR users give up after overcoming a number of
problematic interactions
• We have 2 thresholds: information scent and
frustration threshold
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24. Follow up
2 May 2013 24
Contact
@markelvigo | markel.vigo@manchester.ac.uk
Presentation DOI
http://dx.doi.org/10.6084/m9.figshare.695073
Datasets
http://wel-data.cs.manchester.ac.uk/investigations/2
24th ACM Conference on Hypertext and Social Media
Hypertext 2013