Perception:
Top-Down and Bottom-Up Processing

Top-Down
Goal-driven
 Processing dominated by context, expectations,
hypotheses, "the big picture"


Bottom-Up
Data-driven
 Processing dominated by characteristics of
stimulus, "details”
 Feature analysis


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Both types of processing occur simultaneously
and are highly interactive.
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Some examples

Problem-solving
 Wheel
of Fortune
 Crossword
puzzles
 Design

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Hearing: conversation, listening to music,
etc.
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An example …

Listen to the song and write down the words as
you hear them.

To discuss …
 What
were doing during “bottom-up” processing (with
and without visual cues?
 What
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were you doing during “top-down” processing?
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Perception of print

Feature analysis:



Bottom-up, we perceive features
of letters, letters, words
Involves pattern matching
Top-down, we use context of
surrounding letters and words to
limit alternative interpretations
Examples:
Sawple
Sample
"The majority of people who take this class are Ixx majors."
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Context-Data Tradeoff

Assuming limited display size for text, trade off
context and data quality:

Many words:
High contextual redundancy (easy to comprehend)
 Poor data quality (hard to read)


Few words:
Good data quality (easy to read)
 Low contextual redundancy (hard to comprehend)

 Example:
weather alerts on a heads-up display
WEATHER
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Will encounter bad
weather
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Creating context: Redundancy gain




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The information is presented
in more than one way.
If the viewer is not able to
process the information in
one mode (e.g., color blind)
can rely on another.
Reaction time is faster if
information is presented
redundantly.
Promotes top-down
processing.
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Object perception

Objects are perceived holistically

Empirical evidence on card-sorting tasks:

objects categorized more quickly and accurately
than "separate" displays such as numbers or
words
♣ ♣
4 of Clubs
Carrot
♣ ♣
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Advantages & disadvantages …

Advantages

Disadvantages
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Object perception

Wickens et al. studies:
 object
displays facilitate performance on information
integration tasks
 separable
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Wt., tons
3.4
3.8
4.1
2.2
2.6
2.9
2
2.7
1.9
3.4
8
gpm
GPM, y
5.5
5.9
6.5
3.3
3.6
4.6
2.9
3.6
3.1
4.9
6
4
2
0
0
1
2
3
4
5
Weight, tons
displays support diagnosis tasks
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Examples …
4
A
B
Easy
Difficult
0
2
1
3
# Errors
Phone
2
Difficult
2
Difficult
1
Difficult
Easy
C
0
3
0
Easy
A
Easy
C
B
Phone
4
4
3
3
Total Errors
Total Errors
3
2
2
2
2
1
1
1
0
0
0
A Easy
A Difficult
B Easy
B Difficult
Phone / Dialing Difficulty
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C Easy
C Difficult
A Easy
0
A Difficult
B Easy
B Difficult
C Easy
C Difficult
Phone / Dialing Difficulty
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Implications for display design

Optimize bottom-up processing
 size,
contrast, font (for text), appropriate upper/lower
case
 raw data on object displays

Optimize top-down processing
 avoid
abbreviations & acronyms whenever possible
 provide context (more words in text, recognizable
object displays)
 restrict “vocabulary” (text and picture) and optimize
distinction between words/pictures


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Evaluate tradeoffs
Usability testing in context
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Some fun examples:
http://exp.kyb.tuebingen.mpg.de/web-experiment/list.html
http://www.grand-illusions.com/index.htm
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