botton up vs top down

7/28/2019 Botton Up vs Top Down

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Top-Down versus Bottom-UpPerception

• Top-Down – Perceive the whole and then individual parts as

needed.

– Experience-driven as opposed to stimulus or input-

data driven.

– Quick and highly inferential but also a source of

misperception.

• Bottom-up

– Perceive the individual parts and organize them into a

whole, if possible.

– Information available in the stimulus itself.

Arranged by Dr. Gordon Vessels 2005



Bottom-Up Processing

Prior Knowledge, Experience,etc.

Stimuli Processing

Perception

Stimuli Input

Created by Dr. Gordon Vessels 2005



David Marr’s ComputationalBottom-Up Approach

• Marr wanted to understand mechanismsof vision rather than just behaviorsassociated with it.

• …he wanted to link neurophysiologywith psychology.

• He took an information processing viewof the mind…

• …and aimed to describe perception interms of computations on sense data…

• …to extract high level visual experience.

Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved athttp://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.



Marr’s Stages of VisualProcessing

• Marr proposed there were distinct stages

of processing in visual perception:

» Stage 1: Raw Primal Sketch

» Stage 2: Complete Primal Sketch

» Stage 3: 2½D Sketch

» Stage 4: Full 3D Representation




Stage 1: Raw Primal Sketch

This involves the extraction of information

regarding edges and intensity changes.




Stage 2: Complete Primal Sketch

• After the Raw Primal Sketch…

• Marr [proposed]… we create a

Complete Primal Sketch by grouping

surfaces and common areas.

• The Gestalt Psychologists of the early

19th Century demonstrated manydifferent ways in which we can group

objects.




Stage 3: 2½D Sketch

• After gaining information aboutgroupings and surfaces, the viewer needssome spatial information.

• Marr called this stage the 2½D Sketch toemphasis that this stage does not give afull 3D representation.

• Rather, just an estimate of the spatiallocations of objects and materials inrelation to the viewer.




2½ D Sketch: Depth Cues

• We perceive much information

from which we infer depth:

» Binocular disparity

» Texture gradients

» Occlusion

» Convergence

» Relative Size




Stage 4: 3D Representation

• The final stage of Marr’s theory. • A full 3D description of our spatial

environment involving the

identification of the structure of objects and materials in our visualfield.

• It allows us to work out the 3Denvironment from a non-egocentric

point-of-view.




GregoryonTop-DownPerception • Gregoryproposesthatweuseourprior

“experienceoftheworldtoshapehowweperceive”stimuliweencounterinit.

• HistheoryofperceptioniscalledTop-Down,

•

Whichmeansweuseactivatedconceptualschemasandmemorynetworks(ourstoredknowledge),moreorlessautomaticallyandsubconsciously,toshapeourperceptionsortointerpretoursensoryinput―sometimescorrectlyandsometimesnot.

• Heconfirmedmanyofhistheoreticalpropositionsusingvisualillusionresearch.

Primary source Bell, Vaughan (2004). Perceptions and perceptual distortions, a PPT show accessed athttp://www.cf.ac.uk/psych/home/bellv1/conf/VaughanPerceptionLecture2004.ppt#1. Written permission granted 5-5-05.



Top-Down Processing

Stimuli Processing

Perception

Stimuli Input

Prior Knowledge,Experience, etc.

PersonalityTemperament

Culture

Social Class

ValuesBeliefs

Prejudices

Attitudes

Immediate

Mental Set

Presence of

Authority

Present Fatigue

Energy Level

Prior Stimuli

Perceived

OccupationEducation

Needs, MoodsMental Health

KnowledgeVocabulary

Specific Life

Experiences

Long-term MemorySchemas




If all of these people were at the same football game, who among them was most likely tohave perceived what actually happened on a controversial play where the receiver mayhave fumbled the ball before his knees touched the ground? Whose perceptions were themost bottom up? Whose perceptions were the most top-down and thus influenced andquickened in terms of inference by their present needs, biases, and heightened emotion?

Whose perception may have been the most accurate and objective based on his or herknowledge of the game? When the head referee reviewed the replays, did he use top-down or bottom-up perception primarily? What top-down influence may have made itpossible for his perceptions to have been highly accurate? Did these people literally seesomething different? Do they really believe what they claimed to have seen?



What do you see? A face looking

down? The word Liar in script or

cursive? Those who first read stories

about deception were more inclined

than others to see the word Liar.

What do you see? The

word liar in script or

cursive? A face looking

down? Those shown

artwork with faces were

more inclined thanothers to see the word

liar .

Arranged by Dr. Gordon Vessels 2004



Top-Down &Bottom-Up Processing

Prior Knowledge, Experience,etc.

Stimuli Processing

Perception

Stimuli Input


botton up vs top down

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