Week 5 Lecture and Module Videos - Perception
Concise Version
Perception
Introduction
Perception is closely related to sensation.
Agenda: Overview of perception, approaches to perception, perceptual organization, and attention.
Learning Objectives:
Outline perception and the computational, constructivist, and ecological approaches.
Describe basic processes in perceptual organization.
Outline how we recognize and organize perceptual information.
Explain key processes in attention.
Sensation vs. Perception
Sensation: Input of information from the environment via sense organs and its transmission to the brain.
Perception: Process that selects, organizes, and interprets sensations into meaningful information.
The boundary between sensation and perception is thin.
Approaches to Perception
Textbooks outline three approaches to perception.
Computational Approach
Perception results from nervous system activity that modifies and processes raw sensations into experienced reality.
Neurons respond to aspects of stimuli (e.g., length, color, texture of a pen) and integrate this information into a meaningful percept.
Constructivist Approach
We construct reality by putting together raw sensory information, influenced by expectations of reality.
Analogy: connecting the dots; expectations help us perceive the environment.
Ecological Approach
The environment holds clues that allow us to perceive our surroundings.
Example: crossing the street and using visual and auditory cues to perceive traffic.
Perceptual Organization
Figure-Ground Discrimination
Basic process used to organize perceptual information.
Example: faces/vase picture. We tend to see one figure and lose the other, flipping between experiences.
Gestalt Psychology
Early 20th century psychologists who studied form perception systematically.
Outlined principles used to group pieces of information.
Basic rules to automatically and unconsciously organize sensory input into meaningful information.
Principles of Grouping
Proximity
We group objects together that are close to one another.
Closure
We perceive incomplete figures as complete.
Similarity
We group similar elements together.
Continuity
The brain organizes stimuli into continuous lines or patterns (good continuation).
Additional Grouping Principles (Palmer)
Common Region
Stimuli within a common boundary are perceived as together.
Connectedness
Objects sharing a common boundary are grouped together.
Synchrony
Objects that change together are grouped together.
Perceiving Motion
Motion Parallax
Objects moving at a constant speed appear to move more if they are closer to the observer.
Example: objects in the distance appearing to move slower when in a moving car.
Looming
Objects that enlarge quickly are perceived as moving toward the viewer.
Other Senses
Equilibrium and touch contribute to perceiving motion.
Stroboscopic Illusion
Continual movement perceived from still images flashed in rapid succession (e.g., cartoons).
Questions in the Study of Perception
Is the flow of images across the retina due to movement of objects or our movements?
How do we compensate for the time lag in the perception of movement?
Perceptual Constancy
Perception of objects remains stable despite changes in sensory receptor stimulation.
Size Constancy
Objects do not appear to change in size when viewed from different distances.
Illusions: Ponzo illusion, Muller-Lyer illusion.
Ponzo Illusion: Two figures are the same size, but one appears larger due to its position in the image.
Muller-Lyer Illusion: Two lines are the same size, but one looks bigger.
Shape Constancy
Perceived shape of an object remains the same even when seen at different angles.
Breaks down at extreme angles.
Object Recognition
Bottom-Up Processing
Uses basic feature analysis, starting with raw sensory data and feeding up to the brain.
Top-Down Processing
Begins with observer's expectations and prior knowledge about the world.
Relies on schemas (rules about the world) and perceptual sets (impacted by context and motivation).
Pareidolia
Perception of an image from ambiguous stimuli (e.g., seeing faces in burnt toast).
Driven by top-down processing.
Feature Analysis
Recognizing objects by assembling their features together.
Features are detected, combined, and the pattern is recognized.
Network Processing
Interaction among feature analyzers that detect stimuli and send messages to the brain.
Parallel distributed processing models: recognition occurs via simultaneous operation of connected units.
Object superiority effect: patterns are more likely to be detected in three-dimensional objects rather than random patterns of lines.
Word superiority effect: words are easier to detect than non-words in strings of random letters.
Parallel processing activates interpretations of letters, and the strongest links determine the perceived word.
Attention
Attention is tightly related to perception.
Characteristics of Attention
Selects specific information for further processing.
Allocates mental energy for processing.
Regulates the flow of resources needed to perform a task or coordinate several tasks at once.
Analogy: spotlight in a dark room. Directing attention to one place excludes others.
Improves mental processing.
Takes effort and is limited.
Directing Attention
Overt Orienting
Looking directly at something.
Covert Orienting
Listening to another conversation while seeming to listen to something else.
Voluntary (Goal-Directed) Attentional Control
Uses top-down processing.
Involuntary Attentional Control
Uses bottom-up processing.
Attention and Resources
Change Blindness
Limited attentional resources.
Difficulty recognizing changes in a quickly changing scene.
Inattentional Blindness
Directing attention to one thing excludes other aspects of the environment.
Example: driving while texting is dangerous because attention is directed to the phone, not the road.
Dividing Attention
Attention is a limited resource, so division is imperfect.
Easier if:
One task is automatic.
Tasks use different resources.
Stroop Task
Read the color of the ink, not the word (e.g., the word "blue" printed in red ink).
Harder because the brain automatically processes the meaning of each word, which competes for attention.
Perception: Making Sense of the Senses
The Role of Perception
Perception allows us to make meaning out of our senses and experience the world around us.
Without it, our senses are meaningless. For example, lacking it, a mother's face would be just shapes, and toast couldn't be distinguished from a grease fire.
Perception as Interpretation
Perception is how we order the chaos of our environment, influenced by expectations, experiences, moods, and cultural norms.
Sometimes, what you see is not what you get, as we can fool ourselves.
Raw Data vs. Interpretation
Our eyes feed raw data to the brain, which does the work of perception.
What we see is the realm of the mind, not the eye.
The Influence of Expectations
Expectations influence what we perceive.
By cuing "mammal" or "bird" in the duck-bunny illusion, the demonstrator influenced what the audience saw.
Perceptual Set
Perceptual set refers to the psychological factors that determine how we perceive our environment.
Believing is seeing: sometimes our beliefs influence our perceptions.
Factors Influencing Perceptual Set
Context
Context is a factor. If the duck-bunny image is pictured with Easter eggs, one is more likely to see a bunny.
Culture
Culture is an important part of our perceptual set.
Emotions and Motivations
Emotions and motivations sway our perceptions. A hill may seem steeper if someone is listening to sad music alone than if they're listening to happy music with a friend.
Misleading Perceptual Sets
Perceptual sets can be misleading or even harmful, and they are the basis of optical illusions.
Form Perception
Complexity of Perception
Transforming marks on paper into words, or lumps into a recognizable face, requires complex processing.
Figure-Ground Relationship
How we organize a scene into main objects (figures) and surroundings (ground).
The classic faces-vase illusion showcases the reversible figure-ground relationship.
Also applies to non-visual fields: one's crush at a party vs. all the other background sounds.
Rules of Grouping
Our minds follow rules of grouping to organize stimuli into something coherent.
Proximity
We group nearby figures together.
Continuity
We perceive smooth, continuous patterns.
Closure
We fill in gaps to create whole objects.
Depth Perception
Crucial for Navigating the World
Depth perception helps us estimate an object's distance and shape.
Innate Ability
It is partially innate, as even most babies have it.
Visual Cues
We perceive depth using both binocular and monocular visual cues.
Binocular Cues
Require both eyes; the retinas receive slightly different images.
Retinal Disparity
The brain compares the two images to judge distance.
The closer the object, the greater the difference between the two images.
Monocular Cues
Help determine scale and distance of an object.
Relative Size and Height
Determine the size and distance of objects based on their comparative size.
Linear Perspective
Parallel lines appear to meet as they move into the distance.
The sharper the angle of convergence, the greater the distance will seem.
Texture Gradient
Texture becomes less detailed as your eye follows ridges into the distance.
Interposition or Overlap
When one object blocks another, we perceive it as being closer.
Motion Perception
Inferring Speed and Direction
It can gauged based partly on the idea that shrinking objects are retreating and enlarging objects are approaching.
Easily Tricked
The brain can be easily tricked regarding Motion Perception.
Perceptual Constancy
Consistency in Perception
Perceptual constancy allows us to continue to recognize an object regardless of its distance, viewing angle, motion, or illumination, even as it might appear to change color, size, shape, and brightness depending on the conditions.
Conclusion
How the Brain Works
Your brain constructs your perceptions: senses collect Legos, and your brain builds and rebuilds whatever it perceives.
Summary of the lesson
Forms your perceptual set, how form perception works, and the many visual cues that influence your depth perception.
Detailed Version
Perception
Introduction
Perception is closely related to sensation, acting as the cognitive process that interprets and organizes sensory information to produce a meaningful experience of the world.
Agenda: Overview of perception, approaches to perception, perceptual organization, and attention; exploring how these elements contribute to our understanding of sensory inputs.
Learning Objectives:
Outline perception and the computational, constructivist, and ecological approaches, detailing how each explains the perceptual process.
Describe basic processes in perceptual organization, including Gestalt principles and figure-ground discrimination.
Outline how we recognize and organize perceptual information, integrating both bottom-up and top-down processing.
Explain key processes in attention, such as selective attention, divided attention, and the impacts of attention on perception.
Sensation vs. Perception
Sensation: Input of information from the environment via sense organs and its transmission to the brain, involving the detection of stimuli and their conversion into neural signals.
Perception: Process that selects, organizes, and interprets sensations into meaningful information, giving context and understanding to the raw sensory input.
The boundary between sensation and perception is thin, as perception is influenced by prior knowledge, expectations, and cognitive processes.
Approaches to Perception
Textbooks outline three primary approaches to perception: computational, constructivist, and ecological.
Computational Approach
Perception results from nervous system activity that modifies and processes raw sensations into experienced reality, using algorithms and neural computations to transform sensory data.
Neurons respond to aspects of stimuli (e.g., length, color, texture of a pen) and integrate this information into a meaningful percept, demonstrating how individual features are combined to create a cohesive perception.
Constructivist Approach
We construct reality by putting together raw sensory information, influenced by expectations of reality, which suggests perception is an active process shaped by cognitive frameworks.
Analogy: connecting the dots; expectations help us perceive the environment by filling in missing information and guiding our interpretation of sensory inputs.
Ecological Approach
The environment holds clues that allow us to perceive our surroundings directly, without the need for complex computations or cognitive constructions.
Example: crossing the street and using visual and auditory cues to perceive traffic, illustrating how we directly use environmental information to navigate and interact with our surroundings.
Perceptual Organization
Figure-Ground Discrimination
Basic process used to organize perceptual information, distinguishing between an object (figure) and its background (ground).
Example: faces/vase picture. We tend to see one figure and lose the other, flipping between experiences, which demonstrates the brain's ability to switch between different interpretations of the same visual input.
Gestalt Psychology
Early 20th century psychologists who studied form perception systematically, identifying principles that govern how we perceive patterns and forms.
Outlined principles used to group pieces of information, explaining how our minds automatically organize sensory input into coherent wholes.
Basic rules to automatically and unconsciously organize sensory input into meaningful information, enhancing our ability to perceive structure and order in the world.
Principles of Grouping
Proximity
We group objects together that are close to one another, perceiving them as a unit.
Closure
We perceive incomplete figures as complete, filling in gaps to create a coherent image.
Similarity
We group similar elements together based on features like shape, color, or size.
Continuity
The brain organizes stimuli into continuous lines or patterns (good continuation), following the smoothest path rather than abrupt changes.
Additional Grouping Principles (Palmer)
Common Region
Stimuli within a common boundary are perceived as together, indicating that enclosed elements are seen as a group.
Connectedness
Objects sharing a common boundary are grouped together, suggesting that physical connection leads to perceptual grouping.
Synchrony
Objects that change together are grouped together, indicating that simultaneous changes lead to unified perception.
Perceiving Motion
Motion Parallax
Objects moving at a constant speed appear to move more if they are closer to the observer, creating a depth cue based on relative motion.
Example: objects in the distance appearing to move slower when in a moving car, illustrating how perceived speed varies with distance.
Looming
Objects that enlarge quickly are perceived as moving toward the viewer, triggering an immediate sense of approach.
Other Senses
Equilibrium and touch contribute to perceiving motion, providing additional sensory information that enhances our awareness of movement.
Stroboscopic Illusion
Continual movement perceived from still images flashed in rapid succession (e.g., cartoons), demonstrating how discrete images can create the illusion of continuous motion.
Questions in the Study of Perception
Is the flow of images across the retina due to movement of objects or our movements? This question addresses how we differentiate between self-generated and externally generated motion.
How do we compensate for the time lag in the perception of movement? This explores how our brain corrects for delays in sensory processing to create a seamless experience of motion.
Perceptual Constancy
Perception of objects remains stable despite changes in sensory receptor stimulation, allowing us to recognize objects regardless of varying conditions.
Size Constancy
Objects do not appear to change in size when viewed from different distances, maintaining a stable perception of size despite changes in retinal image size.
Illusions: Ponzo illusion, Muller-Lyer illusion.
Ponzo Illusion: Two figures are the same size, but one appears larger due to its position in the image, demonstrating how depth cues can distort size perception.
Muller-Lyer Illusion: Two lines are the same size, but one looks bigger, illustrating how arrowheads at the ends of lines can influence perceived length.
Shape Constancy
Perceived shape of an object remains the same even when seen at different angles, allowing us to recognize objects despite changes in perspective.
Breaks down at extreme angles, indicating that shape constancy has its limits.
Object Recognition
Bottom-Up Processing
Uses basic feature analysis, starting with raw sensory data and feeding up to the brain, building perception from basic sensory elements.
Top-Down Processing
Begins with observer's expectations and prior knowledge about the world, using existing cognitive frameworks to interpret sensory information.
Relies on schemas (rules about the world) and perceptual sets (impacted by context and motivation), which guide our interpretation of sensory inputs based on prior experiences and expectations.
Pareidolia
Perception of an image from ambiguous stimuli (e.g., seeing faces in burnt toast), driven by the brain's tendency to find familiar patterns.
Driven by top-down processing, where expectations and prior knowledge influence the interpretation of vague sensory information.
Feature Analysis
Recognizing objects by assembling their features together, involving the detection and integration of individual sensory attributes.
Features are detected, combined, and the pattern is recognized, illustrating how perception is built from basic sensory components.
Network Processing
Interaction among feature analyzers that detect stimuli and send messages to the brain, allowing for parallel and distributed processing of sensory information.
Parallel distributed processing models: recognition occurs via simultaneous operation of connected units, indicating that perception arises from the interaction of multiple neural networks.
Object superiority effect: patterns are more likely to be detected in three-dimensional objects rather than random patterns of lines, suggesting that meaningful structures enhance perceptual processing.
Word superiority effect: words are easier to detect than non-words in strings of random letters, demonstrating that context and meaning facilitate perception.
Parallel processing activates interpretations of letters, and the strongest links determine the perceived word, illustrating how multiple interpretations compete to shape perception.
Attention
Attention is tightly related to perception, serving as the mechanism that selects and filters sensory information for further processing.
Characteristics of Attention
Selects specific information for further processing, filtering out irrelevant stimuli to focus on what is important.
Allocates mental energy for processing, directing cognitive resources to the selected information.
Regulates the flow of resources needed to perform a task or coordinate several tasks at once, managing cognitive workload and preventing overload.
Analogy: spotlight in a dark room. Directing attention to one place excludes others, illustrating the selective nature of attention.
Improves mental processing, enhancing the efficiency and accuracy of cognitive operations.
Takes effort and is limited, indicating that our attentional resources are finite.
Directing Attention
Overt Orienting
Looking directly at something, involving physical movements to focus attention.
Covert Orienting
Listening to another conversation while seeming to listen to something else, directing attention without physical movements.
Voluntary (Goal-Directed) Attentional Control
Uses top-down processing, guiding attention based on internal goals and intentions.
Involuntary Attentional Control
Uses bottom-up processing, capturing attention through salient or unexpected stimuli.
Attention and Resources
Change Blindness
Limited attentional resources can lead to change blindness, the difficulty in noticing changes in a quickly changing scene.
Difficulty recognizing changes in a quickly changing scene, demonstrating the limitations of our attentional capacity.
Inattentional Blindness
Directing attention to one thing excludes other aspects of the environment, leading to a failure to notice unexpected objects or events.
Example: driving while texting is dangerous because attention is directed to the phone, not the road, illustrating the risks of divided attention.
Dividing Attention
Attention is a limited resource, so division is imperfect, leading to reduced performance in multiple tasks.
Easier if:
One task is automatic, requiring minimal attentional resources.
Tasks use different resources, reducing interference between tasks.
Stroop Task
Read the color of the ink, not the word (e.g., the word "blue" printed in red ink), which demonstrates the interference between automatic and controlled processes.
Harder because the brain automatically processes the meaning of each word, which competes for attention, creating a cognitive conflict.
Perception: Making Sense of the Senses
The Role of Perception
Perception allows us to make meaning out of our senses and experience the world around us, transforming raw sensory data into a coherent and understandable reality.
Without it, our senses are meaningless. For example, lacking it, a mother's face would be just shapes, and toast couldn't be distinguished from a grease fire, illustrating the critical role of perception in everyday recognition and understanding.
Perception as Interpretation
Perception is how we order the chaos of our environment, influenced by expectations, experiences, moods, and cultural norms, shaping how we interpret sensory inputs.
Sometimes, what you see is not what you get, as we can fool ourselves, demonstrating the subjective nature of perception.
Raw Data vs. Interpretation
Our eyes feed raw data to the brain, which does the work of perception, transforming sensory signals into meaningful experiences.
What we see is the realm of the mind, not the eye, emphasizing that perception is a cognitive construction rather than a direct reflection of sensory data.
The Influence of Expectations
Expectations influence what we perceive, guiding our interpretation of sensory inputs based on prior knowledge and beliefs.
By cuing "mammal" or "bird" in the duck-bunny illusion, the demonstrator influenced what the audience saw, illustrating how priming can shape perception.
Perceptual Set
Perceptual set refers to the psychological factors that determine how we perceive our environment, influencing our interpretation of sensory information.
Believing is seeing: sometimes our beliefs influence our perceptions, demonstrating the power of expectations to shape our experiences.
Factors Influencing Perceptual Set
Context
Context is a factor. If the duck-bunny image is pictured with Easter eggs, one is more likely to see a bunny, showing how surrounding information can influence perception.
Culture
Culture is an important part of our perceptual set, shaping our beliefs, values, and interpretations of the world.
Emotions and Motivations
Emotions and motivations sway our perceptions. A hill may seem steeper if someone is listening to sad music alone than if they're listening to happy music with a friend, illustrating how emotional states can alter perception.
Misleading Perceptual Sets
Perceptual sets can be misleading or even harmful, and they are the basis of optical illusions, demonstrating how expectations can distort our perception of reality.
Form Perception
Complexity of Perception
Transforming marks on paper into words, or lumps into a recognizable face, requires complex processing, illustrating the sophisticated cognitive operations involved in perception.
Figure-Ground Relationship
How we organize a scene into main objects (figures) and surroundings (ground), differentiating between what is central and what is background.
The classic faces-vase illusion showcases the reversible figure-ground relationship, where the same image can be seen as either faces or a vase depending on how attention is directed.
Also applies to non-visual fields: one's crush at a party vs. all the other background sounds, showing how we selectively focus on certain auditory stimuli.
Rules of Grouping
Our minds follow rules of grouping to organize stimuli into something coherent, facilitating our ability to perceive structure and meaning.
Proximity
We group nearby figures together, perceiving them as a unit.
Continuity
We perceive smooth, continuous patterns, following the smoothest path rather than abrupt changes.
Closure
We fill in gaps to create whole objects, completing incomplete figures to form a coherent image.
Depth Perception
Crucial for Navigating the World
Depth perception helps us estimate an object's distance and shape, allowing us to interact effectively with our environment.
Innate Ability
It is partially innate, as even most babies have it, suggesting a biological basis for depth perception.
Visual Cues
We perceive depth using both binocular and monocular visual cues, integrating information from multiple sources.
Binocular Cues
Require both eyes; the retinas receive slightly different images, allowing for stereoscopic depth perception.
Retinal Disparity
The brain compares the two images to judge distance, using the difference between the images to create a sense of depth.
The closer the object, the greater the difference between the two images, allowing for precise depth estimation.
Monocular Cues
Help determine scale and distance of an object, using information from a single eye to infer depth.
Relative Size and Height
Determine the size and distance of objects based on their comparative size, using known sizes to estimate distance.
Linear Perspective
Parallel lines appear to meet as they move into the distance, creating a sense of depth through convergence.
The sharper the angle of convergence, the greater the distance will seem, enhancing the depth perception.
Texture Gradient
Texture becomes less detailed as your eye follows ridges into the distance, providing a cue for depth based on changes in texture density.
Interposition or Overlap
When one object blocks another, we perceive it as being closer, using occlusion as a cue for relative depth.
Motion Perception
Inferring Speed and Direction
It can gauged based partly on the idea that shrinking objects are retreating and enlarging objects are approaching, using changes in size to infer motion.
Easily Tricked
The brain can be easily tricked regarding Motion Perception, leading to illusions of movement.
Perceptual Constancy
Consistency in Perception
Perceptual constancy allows us to continue to recognize an object regardless of its distance, viewing angle, motion, or illumination, even as it might appear to change color, size, shape, and brightness depending on the conditions, ensuring a stable perception of the world.
Conclusion
How the Brain Works
Your brain constructs your perceptions: senses collect Legos, and your brain builds and rebuilds whatever it perceives, illustrating the active and constructive nature of perception.
Summary of the lesson
Forms your perceptual set, how form perception works, and the many visual cues that influence your depth perception, providing a comprehensive overview of the key concepts in perception.
Images
