Top-Down versus Bottom-Up Perception

1
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.

Arranged by Dr. Gordon Vessels 2005
2
Form Perception Feature Analysis
Bottom-Up Processing Relies on properties of the
stimulus such as patterns of light and dark
areas.
Top-Down Processing Relies on higher-level
information such as prior knowledge and
experience.
What is in this picture?
Modeled after a PPT slide created by Kevin
Richardson in 1998 and made available through the
American Psychological Society
3
Bottom-Up Processing
Prior Knowledge, Experience, etc.
Perception
Stimuli Processing
Stimuli Input
Created by Dr. Gordon Vessels 2005
4
David Marrs 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/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
5
Marrs 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/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
6
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/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
7
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.

Source Bell, Vaughan (2004). Perception and
perceptual distortion. A PPT presentation
retrieved at http//www.cardiff.ac.uk/psych/home/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
8
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.

Source Bell, Vaughan (2004). Perception and
perceptual distortion. A PPT presentation
retrieved at http//www.cardiff.ac.uk/psych/home/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
9
2½ D Sketch Depth Cues

• We perceive much information from which we infer
  depth
• Binocular disparity
• Texture gradients
• Occlusion
• Convergence
• Relative Size

Source Bell, Vaughan (2004). Perception and
perceptual distortion. A PPT presentation
retrieved at http//www.cardiff.ac.uk/psych/home/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
10
Stage 4 3D Representation

• The final stage of Marrs 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.

Source Bell, Vaughan (2004). Perception and
perceptual distortion. A PPT presentation
retrieved at http//www.cardiff.ac.uk/psych/home/b
ellv1/ Used here with the authors written
permission. Slide arrangement by Vessels, 2005.
11
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/Vaug
hanPerceptionLecture2004.ppt1. Written
permission granted 5-5-05.
12
Top-Down Processing
Culture Social Class
Values Beliefs
Prejudices Attitudes
Personality Temperament
Occupation Education
Prior Knowledge, Experience, etc.
Immediate Mental Set
Prior Stimuli Perceived
Presence of Authority
Present Fatigue Energy Level

Needs, Moods Mental Health
Knowledge Vocabulary
Specific Life Experiences
Long-term Memory Schemas
Perception
Stimuli Processing
Stimuli Input
Created by Dr. Gordon Vessels 2005
13
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?
14
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.
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.
Arranged by Dr. Gordon Vessels 2004
15
Top-Down Bottom-Up Processing
Prior Knowledge, Experience, etc.
Perception
Stimuli Processing
Stimuli Input
Created by Dr. Gordon Vessels 2005