Stimulus for Neisser‟s visual search...

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