Perception Flashcards
Define ‘perception’
Conscious experience that results from stimulation of the senses
What are the basic characteristics of perception?
- Can change based on added information
- Can involve a process similar to reasoning or problem solving
- Can be based on a perceptual rule
- Occurs in conjunction with action
- Gateway to all other cognition
Why is perception difficult for machines?
- Stimulus on receptors is ambiguous (inverse projection problem)
- Objects can be hidden or blurred
- Objects look different from different viewpoints (viewpoint invariance)
Inverse projection problem
Task of determining the object that caused a particular image on the retina. Humans typically solve this problem easily as compared to computers
Viewpoint invariance
People’s ability to recognize an object seen from different viewpoints
Two types of information used by the human perceptual system
- Environmental energy stimulating receptors
2. Knowledge and expectations
Bottom-up processing aka data-based processing
Processing that starts with information received by the receptors (starts at the bottom, when environmental energy stimulates receptors). Sequence of events from eye to brain.
Top-down processing aka knowledge-based processing
Processing that involves a person’s knowledge or expectation. Enables people to rapidly identify and determine a story behind a scene.
“Multiple personalities of a blob”
Example of top-down processing. What we expect to see in different contexts influences our interpretation of the identity of the “blob”
Speech segmentation
Example of top-down processing. The process of perceiving individual words within the continuous flow of the speech signal. If a listener understands the language, their knowledge of the language creates the perception of individual words
Transitional probabilities
Example of top-down processing. in speech, the likelihood that one speech sound will follow another within a word. Something we learn without realizing.
Likelihood principle
Part of Helmholtz’s theory of unconscious inference that states we perceive the object that is most likely
Unconscious inference
Helmholtz’s idea that our perceptions are the result of unconscious assumptions we make about the environment.
Goes hand in hand with his likelihood principle.
Max Wertheimer
Led Gestalt Psychologists to reject the idea that perceptions were formed by “adding up” sensations.
Stroboscope created an illusion of movement by rapidly alternating two slightly different pictures
Apparent movement
The principle behind the illusion of movement created by the stroboscope.
Occurs when stimuli in different locations are flashed on after another with the proper timing.
Three components of stimuli that create apparent movement:
- One light flashes on and off
- A period of darkness, lasting a fraction of a second.
- The second light flashes on and off
Why don’t we see the period of darkness during apparent movement?
Our perceptual systems adds something during the period of darkness - the perception of light moving
Wertheimer’s two conclusions on apparent movement:
- Apparent movement cannot be explained by sensations because there is nothing in the dark space between flashing lights.
- The whole is different than the sum of its parts
Gestalt psychologists believe that perception is determined by…
specific organizing principles (aka “intrinsic laws”) built into the system
What are the three principles of perceptual organization?
- Good continuation
- Pragnanz
- Similarity
Good continuation
States that points, when connected, result in straight or smoothly curving lines that are seen as belonging together.
Objects that are overlapped are seen as continuing behind the overlapping object.
Pragnanz
“Good figure”
States that every stimulus pattern is seen in such a way that the resulting structure is as simple as possible.
Ex; Olympic circles are seen as 5 circles, not 9 shapes
Similarity
States that similar things tend to be grouped together
Regularities in the environment
Characteristics of the environment that occur frequently
Physical regularities
Regularly occurring physical properties of the environment.
Ex; there are more vertical and horizontal lines in the environment than oblique (angled) lines
Physical regularities: Oblique effect
Vertical and horizontal orientations are perceived more easily than other (slanted) orientations
Physical regularities: Light from above assumption
Our perception of illuminated shapes is influenced by how they are shaded, combined with the brain’s assumption that light is coming from above.
Semantic regularities
The characteristics associated with the functions carried out in different scenes
Semantic regularities: Scene schema
A person’s knowledge about what is likely to be contained in a particular scene. Can help guide attention to different areas of the scene.
Regularities in the environment provide information we can use to…
resolve ambiguities
Bayesian inference
Our estimate of the probability of an outcome is determined by the prior probability (our initial belief) and the likelihood (the extent to which the available evidence is consistent with the outcome)
Experience-Dependent Plasticity
Experience can shape nervous system.
The brain’s function can be tuned to operate best within a specific environment
Empirical evidence: Gauthier - Greeble stimuli
Interaction of perception and action
Coordination is continually occurring between perceiving stimuli and taking action towards them.
Ex; picking up a cup of coffee
“What” pathway
AKA ventral pathway. Associated with perceiving and recognizing objects
Object discrimination problem
Must remember an object based on its shape and choose it when presented with another object after a delay.
This was presented to monkeys in order to conclude that it was associated with the “What” pathway
“Where” pathway
AKA dorsal pathway.
Associated with ability to locate objects
Landmark discrimination problem
Must remember an objects location and choose that location after a delay.
This was presented to monkeys in order to conclude that it was associated with the “Where” pathway
Ungerleider and Mischkin experiment with Monkeys
Studied how removing part of a monkey’s brain (brain ablation) affected its ability to identify an object and determine the objects location
Milner and Goodale experiment with perception and action streams
Studied a woman with damage to her temporal lobe. Her behaviour to the tasks showed that there is one mechanism for judging orientation and other for coordinating vision and action
Perception pathway
Associated with perceiving and recognizing objects.
Corresponds to the “What” pathway
This was damaged in the woman’s brain
Action pathway
Associated with neural processing that occurs when people take action.
Corresponds to the “Where” pathway
Mirror neurons
Discovered in monkeys, no evidence for them in humans.
In the premotor cortex, respond when a monkey observes someone else carrying out an action AND when the monkey itself carries out that action
Cortical areas in the human brain associated with mirror neuron system
Frontal, parietal, and temporal
