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CognitivePsychology
PSY 504
VU
Lesson
14
PATTERNRECOGNITION
We
know how information is
first recorded by senses
andselected for processing
by attentional
mechanisms.The
most criical questionfor a
theory of perception is how is
thisinformation
recognizedfor
what it is?
Mostresearch
has focused on letter
recognition or recognition of letters
identity: forexample
how
do
we recognize
A
as
an instance of
A
TemplateMatching
Models
Thetemplate-matching
theory of perceptionassumes
that a retinal image of an
object is faithfully
transmitted
to the brain. An attempt is
made to compare it directly to
various
storedpatterns.
Thesepatterns
are calledtemplates. So,
the basic is that the
perceptual systemtries to
compare
theletter
to templates it hasfor each
letter andreports the
template thatgives the
bestmatch.
Figureillustrates
various attempts to make
template matching work. In
each case, an attempt
is
made
to achieve a correspondence
betweenthe retinal cells
stimulated by the A and
theretinal
cellsspecified
for a
templatepattern.
Inputrepresents
retinalcells.
Templatematching
Thepattern
is stored for eachretinal
cell activated; if different
retinal cells areactivated
there
won't
be a match. As the figure is
shown:
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CognitivePsychology
PSY 504
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a
successfulmatching
b
wrongmatching
c
successfulmatching
d
wrongpart
of retina
e
wrongsize
f
wrongorientation
g
and
h non-standard images
Examples
in machines
Sometemplate
matching machinesare;
Finger-printmatching
machines. Fingerprints
machine are templatematching
machines.These
machinesmatch
finger prints withcriminal
fingerprints.
Barcode
reading machines in shopping
stores are alsoexample of
template
matchingmachines.
ATM/
Credit card readingmachines.
These machinesmatch the
numbers of ATM card
with
passwords.
Butthese
are machines thatrecognize
exact matches. Any minor
change means there is
no
match.
Humanflexibility
In
Humanswe
canrecognize LARGE letters
andsmall characters,
Characters in the wrong place
and
in strange.
It
means if you meet
youruncle after many
yearseven he is in different
appearanceyou can
recognizehim.
This is humanflexibility to
recognize things,people or
places.
Problemswith
templates
Humanperceptual
system is muchmore
flexible.
Mostpatterns
we encounter undergo at least
some minor
changes.Like,
Lettersare
different font sizesand
styles
Shapeschange
slightly
Orientationsare
different
Butstill
we can
recognizethings.
FeatureAnalysis
model
In
this model, Stimuli
arethought of as combination of
elemental or primitive
features.
Thefeatures
for alphabets mayconsist of
horizontallines
_
verticallines
I
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CognitivePsychology
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Lines
at approx 45 degree
angle/
And
curves (
Likealphabet
T
hastwo
line one verticaland
other is horizontal lineboth
make alphabet
T.
Allletters
are consisted on these four
patterns. Ourmind analyzes
lettersaccording to
thesefeatures.
How
is it better than
templatemodel?
Featuresare
mini-templates butfeatures
are simpler.
Onecan
identify criticalfeatures
for a letter
For
A, 2 45 degree angles (/ \) intersect at
the top and a
horizontalline _
intersects
both
of these near the
middle.the pattern of A
consists of these lines plus
a specification
as
to how they should be
combined.
Thesefeatures
are very muchlike
the output of edgeand
bar detectors in thevisual
cortex.
Example
Many
other details
areunimportant
So,
A
A
A
A
A
A
AAA
All
of the above can be
recognized as the
sameletter. Even they
are in different shapes
and
differentstyles.
In
the feature model we do
notneed a template for
eachletter but only
forevery feature,
this
would
be a great saving. We have 26
letters small and capital.
If letters have
manyfeatures in
common,subjects
are prone to confuse
them.
By
these four features we
canstore all 26
letters.English model is
alsoapplicable in
Urduletters
withthe
addition of Dot (nukta).Urdu
writing is much morecomplex
than English. Urdureading
is
alsodifficult
as well.
Thefeature
model has a number of
advantages over thetemplate
models.
First,since
the features aresimpler, it
is easier to seehow the
system mighttry to correct
forthe
kinds
of difficulties caused by
templatesmodel.
A
second advantage of
thefeature combination
scheme is that it is possible to
specifythose
relationshipsamong
features that aremost
critical to
thepattern.
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