perception. question of the day why is recognizing an object so easy for humans, but so difficult...

Perception

Question of the Day

Why is recognizing an object so easy for humans, but so difficult for computers?

Points of Confusion

http://i.ivillage.com/E/325/Celebrities/FaceReader/FaceReaderIntro_325.jpg

http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg

Perception:attaching meaning to incoming sensory information

What isthis?

The number “4” from the check is compared to a list of

stored templates.

Bottom-Up Processes

Template matching

Problems with Template Matching Large number of stored templates

needed How are new templates made? An object can be “more or less” like the

templateWe can recognize many variations of a

template

Bottom-Up Processes

Figure 2-8

Bottom-Up Processes

Featural Analysis

features (“parts”) of a stimulus are recognized by feature detectors and added together to help us perceive an object

Lines or edges Geons Phonemes Parts of a face (eyes, nose…)

Bottom-Up Processes

Featural Analysis

Geons

Figure 2-14 A depiction of Selfridge’s (1959) Pandemonium model.

Featural

Analysis Letter

detection

Bottom-Up Processes

Featural Analysis

Feature PropertiesDetectors can respond at different

intensitiesConnections between detectors can

have different strengthsIt is possible to change what a

detector will respond to

Bottom-Up Processes

Prototype Matching

http://www.palm.com

Bottom-Up Processes

Prototype Matching

Figure 2-19

An example of context effects in perception.

Top-Down Processes

Top-Down Processes

Perceptual Learning

Top-Down Processes

Change Blindness

http://viscog.beckman.uiuc.edu/grafs/demos/10.html

Word Superiority Effect

Top-Down Processes

K

OWRK

WORK

K D

Bottom-Up and Top-Down Processing working togetherWord Perception Connectionist Model

Features(lines)

Letters

Words

I

B

Bat

_at

Flying Animal

Gestalt Psychology (Wertheimer, Koffka, and Kohler – 1920s)“The whole differs from the sum of its

parts”Perception is not built up from

sensations but is a result of perceptual organization

We use heuristics to make “best guesses” about the identity of stimuli

Theories of Perception

The Gestalt Approach Principles of perceptual organization

Pragnanz - every stimulus is seen as simply as possible

Figure 2-5

Gestalt principles of Perceptual Organization

Gestalt principles of Perceptual Organization

Similarity

http://www.aber.ac.uk

Gestalt principles of Perceptual Organization Good continuation

what most people would see

not this

http://www.aber.ac.uk

The Gestalt Approach Principles of perceptual organization

Good continuation Connected points resulting in straight or smooth

curves belong together Lines are seen as following the smoothest path

http://www.owlnet.rice.edu/~psyc351/Images/Wolfe-Fig-04-07-0.jpg

http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/continuation/continuation_a.gif

Gestalt principles of Perceptual Organization

http://www.aber.ac.uk

Proximity

The Gestalt Approach

Principles of perceptual organization Proximity - things that are near to each other are grouped

together

Gestalt principles of Perceptual Organization

Common fate

http://www.tutkie.tut.ac.jp/~mich/humanmotion.gif

Principles of perceptual organization Meaningfulness or familiarity - things form groups if they

appear familiar or meaningful

The Gestalt Approach

http://www.customflamepainting.com/noncgi_parts/upload/samples.901.11.jpg

Principles of perceptual organization Common region - elements in the

same region tend to be grouped together

Uniform connectedness - connected region of visual properties are perceived as single unit

Synchrony - elements occurring at the same time are seen as belonging together

The Gestalt Approach

Properties of figure and ground The figure is more “thinglike” and more memorable

than ground The figure is seen in front of the ground The ground is more uniform and extends behind

figure The contour separating figure from ground belongs

to the figure

Perceptual Segregation

Perceptual Segregation

Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background

Reversible figure-ground

http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg

Perceptual Segregation

Gestalt principles of Perceptual Organization

Closure

http://daphne.palomar.edu

Figure 3-26 (p. 91)Example of stimuli used in the PET scan study of processing words.

Word Perception Neuropsychological Perspective

Direct Perception vs. Constructivist Approach

Biological motion http://www.psico.univ.trieste.it/labs/acn-lab

/eng_p/e051c1m1_curr.html

Optic flow

Affordances: Information from the stimulus that specifies

how it can be used

Direct Perception

Visual Agnosia

http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg

Visual Agnosia

Associative Visual Agnosia Can copy, but unaware what it

is; cannot assign meaning to object

Difficulty in transferring visual info into words

Apperceptive Visual Agnosia Cannot recognize by shape Cannot copy drawings Often involves ‘prosopagnosia’

http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg

Agnosia

Identification of Faces and Members of Categories

Prosopagnosia

The Fusiform Face Area:

http://www.psy.vanderbilt.edu/faculty/gauthier/picts/mona_lisa.jpg

Perceptual Intelligence

light-from-above heuristic