1. Chapter 3
Perception

2. Some Questions to Consider
Why can two different people experience different perceptions in response to exactly the same stimulus?
How does the brain become tuned to respond best to things likely to appear in the environment?
How does perception depend on a person’s knowledge about characteristics of the environment?
Are there neurons in the visual system that might help us understand other people’s actions?

3. The Complexity of Perception
Bottom-up processing
Perception may start with the senses
Incoming raw data
Energy registering on receptors
Top-down processing
Perception may start with the brain
Person’s knowledge, experience, expectations

4. Definitions
Sensation: absorbing raw energy (e.g., light waves, sound waves) through our sensory organs
Transduction: conversion of this energy to neural signals
Attention: concentration of mental energy to process incoming information
Perception: selecting, organizing, and interpreting these signals

5. Overview: Sensation and Perception
Energy contains information about the world (usually incomplete, full of noise, and distorted)
Accessory structure modifies energy
Receptor transduces energy into a neural response
Sensory nerve transmits the coded activity to the central nervous system
Thalamus processes and relays the neural response
Relayed to specialized areas of the cortex
Perception of the world is created

6. Perception Is…
The process of recognizing, organizing, and interpreting information from senses
Not an exact copy of “the world”
Based on our past experience and expectations

7. 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

8. Bottom-up Processing: Behavioral
Recognition-by-components theory (RBC)
We perceive objects by perceiving elementary features
Geons: three-dimensional volumes
Objects are recognized when enough information is available to identify object’s geons

9. Caption: (a) Some geons; (b) some objects created from the geons on the left. The numbers on the objects indicate which geons are present. (Adapted from “Recognition-by-Components: A Theory of Human Image Understanding,” by I. Biederman, 1987, Psychological Review, 24, 2, pp , Figures 3, 6, 7, and 11, Copyright © 1987 with permission from the author and the American Psychological Association.

10. Caption: An airplane represented (a) by nine geons and (b) three geons
Caption: An airplane represented (a) by nine geons and (b) three geons. (Source: Adapted from “Recognition-by-Components: A Theory of Human Image Understanding,” by I. Biederman, 1987, Psychological Review, 24, 2, pp. 115–147, Figures 3, 6, 7, and 11, Copyright ˝ 1987 with permission from the author and the American Psychological Association.)

11. Geons
Discriminability: geons can be distinguished from other geons from almost all viewpoints
Resistance to visual noise: geons can be perceived in “noisy” conditions
Distinct: 36 different geons have been identified

12. Top-down Processing (Constructive Perspective)
Top-down Processing (Constructive Perspective)
Top-down processing involves making inferences based on context, guessing from experience, and basing one perception on another
Occurs quickly, automatically

13. Caption: “Multiple personalities of a blob
Caption: “Multiple personalities of a blob.” What we expect to see in different contexts influences our interpretation of the identity of the “blob” inside the circles. (Source: Andrew Hollingsworth Memory for object position in natural scenes. Visual Cognition, 12, 1003–1016. Reprinted by permission of the publisher, Taylor & Francis Ltd, Photographs courtesy of Antonio Torralba.)

14. Perceiving Size: Taking Distance into Account
Perceived size is a function of both bottom-up and top-down processing
Bottom-up processing
the size of the image on the retina
Top-down processing
the perceived distance of the object
the size of the object relative to other objects in the environment

15. 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

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

17. Gestalt Laws of Perceptual Organization
Law of good continuation
Lines tend to be seen as following the smoothest path
Caption: We perceive this pattern as continuous interwoven strands because of good continuation.

18. Gestalt Laws of Perceptual Organization
Law of good figure (simplicity or prägnanz)
Every stimulus pattern is seen so the resulting structure is as simple as possible
Caption: Law of simplicity. We see five circles, as in (a), not the more complex array of nine objects, as in (b).

19. Gestalt Laws of Perceptual Organization
Law of similarity
Similar things appear grouped together
Caption: Law of similarity. (a) This display can be perceived as either vertical columns or horizontal rows; (b) more likely perceived as columns of squares alternating with columns of circles, due to similarity of shape

20. Gestalt Laws of Perceptual Organization
Law of familiarity
Things are more likely to form groups if the groups appear familiar or meaningful
Caption: The Forest Has Eyes by Bev Doolittle (1985). Can you find 13 faces in this picture? (Source: “The Forest Has Eyes” 1984 Bev Doolittle, courtesy of The Greenwich Workshop, Inc.)

21. Gestalt Laws of Perceptual Organization
Law of proximity
Things near each other appear grouped together
Law of common fate
Things moving in the same direction appear to be grouped together

22. Gestalt Laws of Perceptual Organization
Gestalt laws often provide accurate information about properties of the environment
Reflect experience
Used unconsciously
Occasionally misleading
Gestalt laws are heuristics

23. Heuristics and Algorithms
Heuristic: “rule of thumb”
Provides best-guess solution to a problem
Fast
Often correct
Algorithm: procedure guaranteed to solve a problem
Slow
Definite result

24. Other Perceptual Heuristics
Light-from-above heuristic
Light comes from above
Is usually the case in the environment
We perceive shadows as specific information about depth and distance
Occlusion heuristic
When object is partially covered by a smaller occluding object, the larger one is seen as continuing behind the smaller occluder

25. Caption: (a) Some of these discs are perceived as jutting out, and some are perceived as indentations. The explanation for this perception is that light coming from above will illuminate (b) the top of a shape that is jutting out and (c) the bottom of an indentation.

26. Neurons and the Environment
Some neurons respond best to things that occur regularly in the environment
Neurons becomes tuned to respond best to what we commonly experience
Horizontals and verticals
Experience-dependent plasticity

27. Caption: Magnitude of brain responses to faces and Greebles (a) before and (b) after Greeble training. The colored areas in the brain records indicate brain activity. The FFA is located within the white squares. (Source: Reprinted with permissions from Gauthier, I., Tarr, M. J.,Anderson, A. W., Skudlarski, P., & Gore, J. C Activation of the middle fusiform “face area” increases with experience in recognizing novel objects. Nature Neuroscience, 2, 568–573.)
Caption: Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble.

28. Perception and Action: What and Where
What stream: identifying an object
Where stream: identifying the object’s location

29. Perception and Action: Using Dissociation Logic
If you are trying to understand a complex system, you can logically deduce conclusions from “malfunctions”
Damage to different areas of the brain cause very different deficits
We can conclude that a specific area is necessary for a specific function
Brain Ablation method allows scientists to damage specific areas of otherwise normal brains (usually in monkeys or cats)
Controlled damage allows for clear conclusions to be drawn

30. Perception and Action: Dissociation Logic
Single dissociation
One function is lost, another remains
Example: Monkey A has damage to temporal lobe. This monkey is no longer able to identify objects (what) but can still identify locations (where)
Therefore, what and where rely on different mechanisms, although they may not operate totally independent of one another

31. Perception and Action: Dissociation Logic
Double dissociation
Requires two individuals with different damage and opposite deficits
Example: Monkey A with temporal lobe damage has intact where but impaired what; Monkey B with parietal lobe damage has intact what but impaired where
Therefore, what and where streams must have different mechanisms AND operate independently of one another

32. Caption: The two types of discrimination tasks used by Ungerleider and Mishkin.
(a) Object discrimination: Pick the correct shape. Lesioning the temporal lobe (purple shaded area) makes this task difficult. (b) Landmark discrimination: Pick the food well closer to the cylinder. Lesioning the parietal lobe makes this task difficult. (From Mishkin, Ungerleider, & Macko, 1983.)

33. Caption: (a) Alice can’t name objects but can accurately reach for them; (b) Bert can name objects, but has trouble accurately reaching for them. This illustrates a double dissociation.

34. Mirror Neurons
Neurons that respond the same way when actually performing an act and when observing someone else perform the act
Located in the premotor cortex
One function of the mirror neurons might be to help understand another person’s actions and react appropriately to them (Rizzolatti & Arbib, 1998; Rizzolatti et al., 2000, 2006)