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Chapter 3

Perception

Some Questions to Consider

  • Why can two different people experience different perceptions in response to the same stimulus?
  • How does perception depend on a person’s knowledge about characteristics of the environment?
  • How does the brain become tuned to respond best to things likely to appear in the environment?
  • How are perception and memory represented in the brain?

Perception Is…

  • Experience resulting from stimulation of the senses
  • Basic concepts
  • Perceptions can change based on added information
  • Involves a process similar to reasoning or problem solving
  • Perceptions occur in conjunction with actions

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Perception Is…

  • It is possible that true human perceptual processes are unique to humans
  • Attempts to create artificial forms of perception (machines) have been met with limited success, and each time have had problems that could not be solved

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Why Is It So Difficult to
Design a Perceiving Machine?

  • Inverse Projection Problem
  • Refers to the task of determining the object responsible for a particular image on the retina
  • Involves starting with the retinal image and then extending outward to the source of that image
  • The brain easily recognizes this as the page of a book, even though it could be many different things.
  • Machines have trouble knowing what it is given the possibilities.

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  • Objects can be hidden or blurred
  • People can often identify objects that are obscured and therefore incomplete, or in some cases objects that are blurry
  • The human brain handles this, machines have trouble.
  • Objects look different from different viewpoints
  • Viewpoint invariance
  • The bicycle looks different.
  • Then human brain handles this easily, machines have trouble.

Why Is It So Difficult to
Design a Perceiving Machine?

Approaches to Understand Perception

  • Direct perception theories
  • Bottom-up processing
  • Perception comes from stimuli in the environment
  • Parts are identified and put together, and then recognition occurs
  • Constructive perception theories
  • Top-down processing
  • People actively construct perceptions using information based on expectations

The Complexity of Perception

  • Bottom-up processing
  • Perception may start with the senses
  • Vision, heating, taste, smell, touch
  • Incoming raw data
  • Energy registering on sensory neurons and receptors
  • Top-down processing
  • Perception may start with the brain
  • Person’s knowledge, experience, expectations

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The Complexity of Perception

The Complexity of Perception

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Hearing Words in a Sentence

  • When you hear words in a sentence spoken in a foreign language, your ability to pick out or understand certain words based on context demonstrates top-down processing (e.g., listening to a baseball game that is broadcast in Spanish may make it easier to hear players names or certain “baseball-related” words)
  • Speech segmentation
  • The ability to tell when one word ends and another begins

Experiencing Pain

  • Direct Pathway model
  • An early model that emphasized nociceptors that would send pain messages directly to the brain
  • A bottom-up processing model

More recent models have found that expectations, attention, and distraction can affect how we experience pain in a “top-down” manner

Helmholtz’s Theory Of
Unconscious Inference (~1860)

  • Top-down theory
  • Some of our perceptions are the result of unconscious assumptions we make about the environment
  • We use our knowledge to inform our perceptions
  • We infer much of what we know about the world
  • Likelihood principle: we perceive the world in the way that is “most likely” based on our past experiences

Helmholtz’s Theory Of
Unconscious Inference (~1860)

Perceptual Organization

  • “Old” view – structuralism
  • Perception involves adding up sensations
  • “New” view – Gestalt psychologists
  • The mind groups patterns according to laws of perceptual organization

Gestalt Laws of Perceptual Organization

  • Law of good continuation
  • Lines tend to be seen as following the smoothest path

Gestalt Laws of Perceptual Organization

  • Law of pragnanz (simplicity or good figure)
  • Every stimulus pattern is seen so the resulting structure is as simple as possible

Gestalt Laws of Perceptual Organization

  • Law of similarity
  • Similar things appear grouped together

Gestalt Laws of Perceptual Organization

Gestalt Laws of Perceptual Organization

  • Gestalt laws often provide accurate information about properties of the environment
  • Reflect experience
  • Experience is important but does not overcome perceptual principles
  • Gestalt laws are intrinsic

Physical Regularities

  • There are certain characteristics of the environment that occur frequently
  • There are more vertical and horizontal orientations than angled or oblique
  • Oblique effect
  • People can perceive verticals and horizontals more easily than other orientations
  • Light-from-above assumption
  • Light comes from above
  • Is usually the case in the environment
  • We perceive shadows as specific information about depth and distance

Physical Regularities

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Semantic Regularities

  • The meaning of a given scene is related to what is happening within that scene, and semantic regularities are the characteristics associated with the functions carried out in different types of scenes.
  • A scene schema is the knowledge of what a given scene ordinarily contains (e.g., if you think of a professor’s office, what would you expect to find/see there?)

Bayesian Inference

  • Thomas Bayes (1701-1761)
  • One’s estimate of the probability of a given outcome is influenced by two factors:

The prior probability (our initial belief about the probability of an outcome)

The likelihood of a given outcome

  • These factors set up an equation, as seen in figure 3.26

Bayesian Inference

Neurons and the Environment

  • Some neurons respond best to things that occur regularly in the environment
  • Neurons become tuned to respond best to what we commonly experience
  • Horizontals and verticals
  • Experience-dependent plasticity
  • The structure of the brain can be influenced by experience
  • The brain is not fixed at birth; experience is very important and changes the brain itself throughout life.
  • Rosenzweig, Bennett, & Diamond (1972)
  • Three groups of 12 rats
  • Standard housed group
  • Impoverished group
  • Enriched group
  • Results for enriched group
  • Cerebral cortex bigger
  • Greater enzyme activity
  • More glial cells
  • Larger neurons and more chemical activity
  • Synapses 50% larger

Neurons and the Environment

  • London taxi-drivers must show mastery of map of the city.
  • Those who pass the test develop more grey matter in the posterior hippocampus (which is involved in memory).
  • BUT, they struggle more than most drivers to adapt to changes in the road network or to driving in unfamiliar cities.

Neurons and the Environment

Movement Facilitates Perception

  • Movement helps us perceive things in our environment more accurately than static, still images
  • For example, a horse in the distance standing still may be more difficult to discern than the horse walking across the field
  • Walking around that same horse to see it from different angles will also facilitate accurate perception

The Interaction of Perception and Action

  • Our actions within or upon the environment around us involve a constant stream of updating perceptions and recognition of very subtle changes

Perception and Action: What and Where

  • What stream: identifying an object
  • Where stream: identifying the object’s location

Perception and Action: What and Where

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