stimulus for neisser‟s visual search...
TRANSCRIPT
Stimulus for Neisser‟s
(1964) visual search
experiment
Where is the letter Z?
Why does „b‟ take longer
than „a‟?
Feature Search
Allows participants to respond quickly
regardless of number of distractors
Pop-out effect
Conjunctive Search (without pop-out)
Participants must study each item individually
until the target is identified.
Hyp: Search time increase with the number of
distractors
What search method is used to identify the blue-
yellow-red molecule in the pictures below?
Treisman‟s Visual search results
- Feature search:
-RT not affected by
increase in # distractors
-Pop-out effect
- Conjunction search:
-RT increased as the #
of distracters increased
-Focused attention
search
CogLab data
N = 11; Fall 2010
Why does Treisman‟s theory predict the visual search findings.
Treisman‟s Feature Integration
Theory
Automatic Controlled or focused attention
How do we perceive objects?
How do we perceive features as part of the
same object?
http://weblamp.princeton.edu/~p
sych/psychology/research/treis
man/index.php
Treisman & Schmidt (1982) Illusory conjunctions
1 8
Task: Report black numbers and then 4 objects
Hypothesis: If features exist independently, then
initially they can be incorrectly combined
Treisman & Schmidt (1982) Illusory conjunctions
Purpose: Find support for pre-attentive stage
Method 1: Flash display 200ms; mask
Ss report black #s then objects at 4 locations
Result 1: Incorrect combinations on 18% of trials
Purpose: Find support for attention stage
Method 2: Flash display 200ms; mask
Ss told to ignore #s, focus attention on objects to report
Result 2: Eliminates incorrect combinations
Treisman & Schmidt (1982)
Does prior knowledge change perception?
Method
Give Ss description of objects (“carrot, lake, tire”)
Flash display of #s/objects 200 ms; mask
Ask to report #s then objects
Results
Significantly reduce # of illusory conjunctions
Conclusion
“Top-down” knowledge changes perception
Or able to “bind” features together more rapidly?
Feature-based perception theories
Treisman conclusions:
Illusory conjunctions occur b/c beginning of perception
(before attention) features are independent -“free floating”
Binding features together or to objects requires attention
After focused attention stage can “perceive” object
Problems with feature theories:
How does brain pull all the feature information together?
How do theories deal with complex objects?
Selective attention
When does selective attention occur?
Is it different for:
Auditory vs. visual selective attention
Type of task
Memory load
Processing or decision stage
Green & Bavelier (2003) Flanker compatibility task
Task:
Detect target in the
rings and ignore
outside shape
IV: “flanker” (distractor)
is same or different as
target
IV: low or high load
DV: RT
Task: Is there a square or
diamond in any of the rings?
Green & Bavelier (2003)
Flanker task results Interference large when low-load target task
Interference small when high-load target task
Less resources to process irrelevant distractor
Low load High load
Normal Ss
Green & Bavelier (2003)
Flanker task results FOR VIDEO GAMERS! Interference large when low-load target task
Interference (still) large when high-load target task
Have enough resources to process the distractor!
Non-video game players
Video game players
Selective attention
Question: How much do we process when selectively attending
to information? Or when does selection occur?
Method: Auditory: Dichotic listening (w. or w.o shadowing) Visual: Stroop effect, Simon effect, Flanker test
Results/Theories Evidence for early, intermediate and late selection Evidence for interference for info not attending to
Discussion Effects depend on availability of resources and power
of unattended stimuli