Unit 2.1: Perception

Key Point: Perception combines BOTH processes — bottom-up provides the data, top-down gives it meaning[web:111].

💡 Examples

Schemas

Schemas are organized mental frameworks or patterns of thought that help us categorize and interpret information based on past experiences[web:111].

How Schemas Work:

• Develop through experience and learning
• Become more complex over time
• Guide top-down processing
• Help you predict and interpret sensory input quickly
• Can lead to biased interpretations or stereotypes

Perceptual Set

A perceptual set is a predisposition or mental tendency to perceive things in a certain way based on expectations, context, motivation, and emotion[web:111].

Effects of Perceptual Sets:

• Cause us to see what we expect to see
• Lead to selective attention
• Result in misinterpretation of ambiguous stimuli
• Can be influenced by motivation and emotion
• Filter what we notice and ignore

Context Effects

Context refers to the surrounding environment and circumstances that influence how we interpret sensory information[web:111].

How Context Influences Perception:

• The same stimulus can be perceived differently depending on surroundings
• Lighting conditions affect color and brightness perception
• Social context influences interpretation of behavior
• Temporal context (time of day, season) shapes expectations

Cultural Influences

Culture shapes perception through learned norms, values, and experiences[web:111].

Cultural Factors:

• Social norms and values — what's considered important or appropriate
• Cultural expectations — how people should behave
• Communication styles — verbal and nonverbal
• Interpretation of symbols and gestures
• Different attention patterns (holistic vs. analytic perception)

Key Insight: People from different cultures can perceive the same stimulus differently because their schemas and perceptual sets are shaped by different experiences[web:111].

Figure-Ground

The ability to distinguish objects (figure) from their background (ground)[web:111][web:114][web:115].

Example: Reading black text on white paper — the text is the figure, the paper is the ground. The famous Rubin's vase illusion shows how figure and ground can reverse (vase vs. two faces)[web:111].

Proximity

Objects that are close together are perceived as belonging to the same group[web:111][web:114][web:115].

Example: Dots arranged in clusters appear as groups rather than scattered individual dots. The closer objects are, the more likely we perceive them as a unit[web:115].

Similarity

Objects that look similar (same color, shape, size, or texture) are perceived as belonging together[web:111][web:114][web:115].

Example: A collection of blue circles and red squares — you naturally group all blue circles together and all red squares together based on similarity[web:115].

Closure

The brain fills in missing information to perceive complete, whole objects even when parts are missing[web:111][web:114][web:115].

Example: Seeing a circle even when there are gaps in the outline, or recognizing a word when some letters are missing (like "A_PL_" → "APPLE")[web:115].

Continuity

The brain perceives smooth, continuous patterns rather than disjointed or discontinuous ones[web:111][web:115].

Example: Looking at intersecting lines, you perceive smooth, flowing lines rather than multiple disconnected segments. Movies appear as continuous motion rather than individual frames[web:115].

Additional Gestalt Principles

💡 Why Gestalt Matters

Gestalt principles explain how we make sense of complex visual information quickly. Instead of analyzing every detail, the brain groups stimuli into meaningful wholes, allowing efficient perception[web:115].

What is Attention?

Attention acts as a filter that helps us focus on relevant information while ignoring distractions, essential for effective perception[web:111].

Types of Attention:

• Selective Attention: Focusing on specific stimuli while filtering out others
• Divided Attention: Processing multiple inputs simultaneously (multitasking)
• Sustained Attention: Maintaining focus over extended periods

Selective Attention: Cocktail Party Effect

The cocktail party effect demonstrates selective attention — the ability to focus on one conversation in a noisy room while still noticing personally relevant information (like your name) from other conversations[web:111].

How It Works:

• Top-down processes (expectations, goals) bias what your brain monitors
• Bottom-up salience (sudden loud voice, your name) can grab attention
• Attention filter lets most unattended input stay out of awareness
• Highly meaningful items can still break through the filter

Inattentional Blindness

Inattentional blindness occurs when we fail to notice obvious stimuli because our attention is focused elsewhere[web:111].

Famous Example: The "Invisible Gorilla" experiment — people watching a video and counting basketball passes fail to notice a person in a gorilla suit walking through the scene[web:111].

Change Blindness

Change blindness is the failure to detect significant changes in a visual scene when attention is not focused on the changing element[web:111].

Example:

• The "door study" — a person asks for directions, and during the conversation, workers carry a door between them. When the door passes, the person asking for directions is swapped with someone else, and many subjects don't notice the change[web:111]
• "Flicker" experiments where objects appear and disappear in photos

Key Point: Change blindness shows how perception relies on selective attention and top-down expectations. We don't perceive everything — only what we attend to[web:111].

Binocular Depth Cues

Binocular cues require both eyes and provide crucial information about distance through the slight differences between the images each eye receives[web:111][web:114].

Monocular Depth Cues

Monocular cues allow depth perception using just one eye. These cues are essential for creating depth in 2D images like paintings and photographs[web:111][web:114].

What are Perceptual Constancies?

Perceptual constancies help us maintain stable perceptions of objects despite changes in the retinal image caused by viewing conditions[web:111][web:116].

These constancies allow us to recognize objects under different conditions and navigate our environment effectively[web:116].

Size Constancy

We perceive objects as maintaining their size regardless of distance from us, even though the retinal image changes[web:111][web:116].

Example: A person walking away from you doesn't appear to shrink, even though their image on your retina gets smaller. You know they remain the same size[web:116].

Shape Constancy

We perceive objects as maintaining their shape despite changes in viewing angle[web:111][web:116].

Example: A door viewed at different angles (open vs. closed) appears to maintain its rectangular shape, even though the retinal image changes from a rectangle to a trapezoid[web:116].

Brightness (Color) Constancy

We perceive objects as maintaining their brightness and color despite changes in lighting conditions[web:111][web:116].

Example: A white shirt appears white whether viewed in bright sunlight or dim indoor lighting, even though the amount of light reflecting off it changes dramatically[web:116].

💡 Constancies and Visual Illusions

Visual illusions often exploit perceptual constancies by providing misleading depth or context cues. For example, the Müller-Lyer illusion tricks size constancy, and brightness illusions exploit contrast and assumptions about lighting[web:111].

What is Apparent Movement?

Apparent movement is the perception of motion when viewing static images or discrete stimuli[web:111].

The brain uses patterns over time (bottom-up sensory input) plus expectations and Gestalt grouping to "fill in" motion between separate events[web:111].

Stroboscopic Movement

The illusion of movement created by the rapid succession of still images[web:111].

Examples:

• Movies and animation — 24+ frames per second create smooth motion
• Flip books — pages flipped rapidly appear as moving images
• Digital displays — rapidly refreshing screens

Phi Phenomenon

The illusion of movement between two stationary stimuli that are flashed in quick succession[web:111].

Example:

• Neon signs — lights blink in sequence, creating the appearance of movement
• Marquee lights — appear to "chase" around theater signs
• Two lights flashing alternately appear as one light moving back and forth

Key Point: The brain links successive sensory events into a single moving object, showing how top-down processing helps interpret ambiguous input as motion[web:111].

Multiple Choice Tips

• Distinguish bottom-up (sensory data) vs. top-down (expectations/schemas) processing[web:111]
• Master Gestalt principles: figure-ground, proximity, similarity, closure, continuity[web:111][web:115]
• Know attention phenomena: cocktail party effect, change blindness, inattentional blindness[web:111]
• Memorize depth cues: Only 5 monocular cues tested (relative clarity, relative size, texture gradient, linear perspective, interposition) + 2 binocular cues (retinal disparity, convergence)[web:111]
• Understand constancies: size, shape, brightness/color[web:111][web:116]
• Recognize apparent movement: stroboscopic movement, phi phenomenon[web:111]

Free Response Question (FRQ) Tips

• Use precise terminology: schemas, perceptual set, Gestalt principles, depth cues, constancies[web:111]
• Apply concepts to scenarios: Explain how schemas create perceptual sets, how Gestalt principles organize visual information[web:111][web:115]
• Distinguish internal vs. external factors: schemas/expectations vs. context/culture[web:111]
• Provide concrete examples: cocktail party effect for selective attention, door study for change blindness[web:111]
• Link to processing types: Show how bottom-up and top-down processing interact[web:111]

🔑 The Big Picture

Perception organizes and interprets sensory information through bottom-up (sensory data) and top-down (expectations, schemas) processing. Internal factors (schemas, perceptual sets) and external factors (context, culture) influence what we perceive. Gestalt principles (figure-ground, proximity, similarity, closure, continuity) explain how we organize visual information into wholes. Attention acts as a filter (selective attention, cocktail party effect, change blindness, inattentional blindness). Depth perception uses binocular cues (retinal disparity, convergence) and monocular cues (relative clarity, relative size, texture gradient, linear perspective, interposition). Perceptual constancies (size, shape, brightness) maintain stable object recognition. Apparent movement (stroboscopic, phi phenomenon) creates motion perception from static images[web:111].

💡 Essential Concepts

• Bottom-up processing
• Top-down processing
• Schemas
• Perceptual set
• Context effects
• Cultural influences
• Figure-ground
• Proximity
• Similarity
• Closure
• Continuity
• Selective attention
• Cocktail party effect
• Inattentional blindness
• Change blindness
• Retinal disparity
• Convergence
• 5 monocular cues
• Size constancy
• Shape constancy
• Brightness constancy
• Stroboscopic movement
• Phi phenomenon