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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
- http:// www.nbcnews.com/video/rock-center/49849152
- The Placebo Effect
- https:// www.youtube.com/watch?v=udJ31KKXBKk
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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