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Chapter 9

Chapter 9 reading


Department
Psychology
Course Code
PSY270H1
Professor
Gillian Rowe
Chapter
9

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PSY270 Lecture 8
Chapter 9
Knowledge & Categorization
Concept: mental representation that is used for a variety of cognitive functions (memory, reasoning, language)
Categorization: function of concepts, process by which things are placed into categories.
oEssential tool for understanding of the world, especially things weve never seen before.
oProvides information about item in category
How are objects placed into categories
Why definitions dont work for categories
Definitio n al ap proa c h to c a teg o riz a tio n: we pla c e obje c ts into c a teg o ri e s b a s e d o n whether it
me e ts the d efinition of the c a teg o ry. (eg. sq u are plane wit h 4 equal side s)
However, many n atural obje c ts an d h u man made obje c ts, d efinitio n s do not work well.
oChair: pie c e of furniture consistin g of s e a ts, legs, b a ck… most chairs h ave such, b u t there
Witt genstein : family re s e mblanc e ” ide a : things in a p ar ticular c a teg o ry re s e mble o n e an o ther in
a n u mber of ways, which allows for v ari atio n.
o c a teg o riz ation is b a s e d o n d etermining h ow si mil ar an o bje c t is to some stan d ard
The prototype approach: finding the average case
prototy p e ap proa c h to c a teg oriz a tio n: membership in a c a teg o ry is d etermined by comparin g
o bjec t to a prototy p e (ty pic al member) that repre s e nts the c a teg ory.
Rosc h: propos e d that the ty pic al prototy p e is b a s e d o n an average of members of a c a teg ory
that are com m o nly ex p eri enc e d.
oBird eg. spar r ows, ro bins, blue jays
oPrototy pic ality: v ari atio n s wit hin c a teg o ri e s a s repre s e ntin g differenc e s (owls, p enguins)
oHigh prototy pic ality: c a teg o ry member clos ely re s e mble s c a teg o ry prototy p e
oLow: d o e s n o t clos ely re s e mble ty pic al member of c a teg ory.
oExp eri ment: pre s e nted p ar ticipants wit h c a teg o ry titl e bird/furnit ure an d a list of
ab o u t 5 0 members of the c a teg ory.
Par ti cipants rate extent member repre s e nted c a teg o ry o n 7 p oint s c ale (1: hig h, 7:
Most agre e d o n “ s parr ow an d chair/sofa a s the ty pic al member.
Most agre e d o n bat an d telep h o n e ” a s least ty pic al member.
Prototypical objects have high family resemblance
oRosch & Mervis: asked participants to describe characteristics ofchair, sofa, mirror, telephone
found that when items characteristics has a large overlap with other items of a category, meant family
resemblance is high. (little = low)
strong relationship b/w family resemblance & prototypicality.
Statements about prototypical objects are verified rapidly
oSmith et al : used procedure called “sentence verification technique” to determine how fast people could answer
questions about an objects category.
given statements, say “yes” if agree,no” if not.
Responded faster for objects high in prototypicality
typicality effect – ability to judge highly prototypical objects rapidly
Prototypical objects are named first
oMervis et al : named objects high in prototypicality first when asked to list a category
Prototypical objects are affected more by priming
oPriming: presentation of one stimulus facilitates response to another usually followed closely in time
oRosch : demonstrated that prototypical members of a category are affected by a priming stimulus more than
nonprototypical members.
Participants first given the prime (eg. color green), then 2 seconds later saw two colours side by side
and indicated by pressing a key as quickly as possible if colours were same or different.
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PSY270 Lecture 8
Chapter 9
Side by side colours paired in 3 ways
oSame – good examples
oSame – poor examples
oDifferent colours
Found that priming resulted in fastersame” judgments than different.
When heargreen, they imagine a “good” (hyighly prototypical) green.
The Exemplar approach: thinking about examples
exemplar ap proa c h to c a teg oriz a tio n: involve s d eterminin g whether an o bje c t is si mil ar to a
oinvolve s many example s (u nlike prototy p e o n e)
oExemplers: a c tual members of the c a teg o ry that a p erso n h a s encountered in the p a s t
Eg. if p erso n h a s encountered spar r ow/ro bins in the p a s t, the s e wo uld b e an
exemplar for the c a teg o ry birds
oExplains the ty pic ality effe c t o bje c ts that are like more of the exemplars are cla s sifi ed
Which works better – prototypes or exemplars?
Exemplars: by u sing re al example s, it c a n e a sily take into a c c ount aty pic al c a s e s (eg. fligh tle s s
birds) inste a d of comparin g a p enguin to an “ a verage ” bird.
oDoe s nt dis c ard information that mi ght b e u s eful later
oRepre s e nts aty pic al birds (pen g uins, o striche s)
oReq uir e s u s to remember only some of the s e v aryin g example s .
Stu die s: co n clud ed that p eo ple may u s e b o th ap proa c he s .
oWhen we initi ally le arn a c a teg o ry, may average exemplars into prototy p e s an d later
some of the exemplar information b e c ome s st ro n g er.
During e a rly le arnin g, p oor at takin g a c c ount “ exc e ptio n s but later exemplars for
the s e c a s e s wo uld b e ad d ed to the c a teg ory.
oExemplar may work b e s t for small c a teg o rie s (eg. US pre sidents) an d prototy p e b e s t for
we kn ow g enerally what c a ts are (prototy p e), b u t we spe cific ally o u r own c a t the b e s t
oblen ding of prototy p e s & exemplars
Is there a psychologically “privileged” level of categories?
hierarchic al organiz a tio n: g eneral c a teg o ri e s are divided into small er, more spe cific c a teg o ri e s ,
cre a ti n g n u mber of levels of c a teg o ri e s
Roschs approach: whats special about basic level categories?
glob al (su p erordinate) b a sic spe cific (subordinate)
furnit ure table kitchen table
reaso n ed that gre a ter n u mber of fe a ture s provide s more information ab o u t a c a teg ory
ofrom b a sic 9 com m o n fe a ture s
glob al 3, los e a lot of informatio n
spe cific 1 0 . 3 , g ain just a littl e information
How knowledge can affect categorization
Tanaka & Taylor: “ ex p er t ex p eri ment.
oExp er t s u s e d more spe cific c a teg o ri e s to n ame birds
oNon ex p er t s: u s e d b a sic c a teg o ri e s .
Peo ple wit h more ex p eri enc e an d familiarity wit h a p ar ticular c a teg ory ten d to focus on more
spe cific information wit h the spe cific level.
oAbility to c a teg oriz e is le arned from ex p erienc e.
Representing relationships between categories: semantic networks:
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