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Perception. Question of the Day. Why is recognizing an object so easy for humans, but so difficult for computers?. Points of Confusion. Perception:

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Question of the day
Question of the Day

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

Points of confusion
Points of Confusion



attaching meaning to incoming sensory information

What is


Figure 2 1 distal stimuli proximal stimuli and percepts
Figure 2-1Distal Stimuli, Proximal Stimuli, and Percepts.


Perceptual Constancies

  • Shape Constancy

    • Tendency to see an object as keeping its form despite changes in orientation.


Perceptual Constancies

  • Size Constancy

    • Tendency to view an object as constant in size despite changes in the size of the retinal image.

Gestalt approach figure ground figure 2 2
Gestalt ApproachFigureGround Figure 2-2

Gestalt approach subjective contours figure 2 3
Gestalt ApproachSubjectiveContoursFigure 2-3

Gestalt principles of perceptual organization
Gestalt principles of Perceptual Organization

  • Proximity

Gestalt principles of perceptual organization1
Gestalt principles of Perceptual Organization

  • Similarity


Gestalt principles of perceptual organization2

not this

what most people

would see

Gestalt principles of Perceptual Organization

  • Good continuation


Gestalt principles of perceptual organization3
Gestalt principles of Organization

  • Closure

Gestalt principles of perceptual organization4
Gestalt principles of Organization

  • Common fate

Figure 2 5
Figure 2-5

Gestalt principles of Perceptual Organization

Two interacting aspects of perception
Two Interacting Aspects of Perception

  • Bottom-up processing

    • Processing based on incoming stimuli from the environment

    • Also called data-based processing

  • Top-down processing

    • Processing based on the perceiver’s previous knowledge

    • Also called knowledge-based processing

The number 4 from the check is compared to a list of stored templates

Bottom-Up Processes

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




Bottom-Up Processes

Problems with Template Matching

  • Large number of stored templates needed

  • How are new templates made?

  • An object can be “more or less” like the template

    • We can recognize many variations of a template

Figure 2 8

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…)


Featural Analysis


Figure 2 14 a depiction of selfridge s 1959 pandemonium model
Figure 2-14 depiction of Selfridge’s (1959) Pandemonium model.





Bottom up processes
Bottom-Up Processes

Featural Analysis

Feature Properties

  • Detectors can respond at different intensities

  • Connections between detectors can have different strengths

  • It is possible to change what a detector will respond to

Bottom up processes1
Bottom-Up Processes

Prototype Matching


Bottom-Up Processes

Prototype Matching