Top-Down versus Bottom-Up Perception Top-Down –Perceive the whole and then individual parts as...

Top-Down versus Bottom-Up Perception

Top-Down versus Bottom-Up Perception

• 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.

• 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 ProcessingStimuli Processing

PerceptionPerception

Stimuli InputCreated by Dr. Gordon Vessels 2005

David Marr’s Computational Bottom-Up Approach

• Marr wanted to understand mechanisms of vision rather than just behaviors associated with it.

• …he wanted to link neurophysiology with psychology.

• He took an information processing view of the mind…

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

• …to extract high level visual experience.Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at

http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Marr’s Stages of Visual Processing

• 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

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

Stage 1: Raw Primal Sketch

This involves the extraction of information regarding edges and

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

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 many different ways in which we can group objects.


Stage 3: 2½D Sketch

• After gaining information about groupings and surfaces, the viewer needs some spatial information.

• Marr called this stage the 2½D Sketch to emphasis that this stage does not give a full 3D representation.

• Rather, just an estimate of the spatial locations of objects and materials in relation to the viewer.


2½ D Sketch: Depth Cues2½ D Sketch: Depth Cues

• We perceive much information from which we infer depth:

» Binocular disparity

» Texture gradients

» Occlusion

» Convergence

» Relative Size

• 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 visual field.

• It allows us to work out the 3D environment from a non-egocentric point-of-view.


Gregory on Top-Down Perception • Gregory proposes that we use our prior

“experience of the world to shape how we perceive” stimuli we encounter in it.

• His theory of perception is called Top-Down,

• Which means we use activated conceptual schemas and memory networks (our stored knowledge), more or less automatically and subconsciously, to shape our perceptions or to interpret our sensory input ― sometimes correctly and sometimes not.

• He confirmed many of his theoretical propositions using visual illusion research.

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

Top-Down Processing



Stimuli Input

Prior Knowledge, Experience, etc. Prior Knowledge, Experience, etc.

Personality Temperament

Culture Social Class

Values Beliefs

Prejudices Attitudes

Immediate Mental Set

Presence of Authority

Present Fatigue Energy Level

Prior Stimuli Perceived

Occupation Education

Needs, Moods Mental Health

Knowledge Vocabulary

Specific Life Experiences

Long-term Memory Schemas

Created by Dr. Gordon Vessels 2005

If all of these people were at the same football game, who among them was most likely to have perceived what actually happened on a controversial play where the receiver may have fumbled the ball before his knees touched the ground? Whose perceptions were the most bottom up? Whose perceptions were the most top-down and thus influenced and quickened 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 her knowledge 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 it possible for his perceptions to have been highly accurate? Did these people literally see something 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 than others to see the

word liar.

Arranged by Dr. Gordon Vessels 2004

Top-Down & Bottom-Up Processing





Stimuli InputCreated by Dr. Gordon Vessels 2005

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