Unit 2.1 Review – Perception

Unit 2.1 Review – Perception

Verified for 2025 AP® Psychology Exam

Overview

Perception is how we interpret sensory information using both raw input (bottom-up) and prior knowledge (top-down). Factors like schemas, context, attention, and Gestalt principles all play a role in shaping what we perceive and how we organize it.

1. How We Process Sensory Info

Perception isn’t just about seeing or hearing — it’s about how your brain interprets that sensory input.

Bottom-Up Processing

  • Starts with raw sensory data (sense receptors → brain)

  • Used when info is new, unclear, or unfamiliar

  • Example: Trying to identify an unfamiliar object by looking closely at its features

Top-Down Processing

  • Driven by what you already know — schemas, memory, expectations

  • Brain fills in the “gaps” or interprets ambiguous info

  • Example: Being able to read messy handwriting because you already know the topic

2. Internal Influences on Perception

What’s going on inside your mind affects how you perceive the world.

Schemas

  • Mental frameworks that help organize and interpret info

  • Built from experience — guide what we pay attention to or ignore

Perceptual Set

  • Tendency to perceive something a certain way due to expectation, emotion, or experience

  • Can cause you to “see what you expect to see”

  • Influenced by motivation, mood, or context

3. External Influences on Perception

Your surroundings and background also shape what and how you perceive.

Context

  • The setting or situation alters interpretation

  • Example: Listening to a sentence in a noisy room vs. quiet classroom

Culture & Experience

  • Cultural norms, communication styles, and previous experience can change what you notice or how you interpret things

  • Can impact how you understand facial expressions, symbols, or visual illusions

4. Gestalt Principles: How We Organize What We See

Gestalt psychology says we naturally organize sensory info into patterns or wholes instead of just individual parts.

Must-Know Laws

  • Closure: Brain fills in gaps to complete a whole shape

  • Figure-Ground: We separate objects (figure) from surface/background (ground)

  • Proximity: Things close together are grouped together

  • Similarity: We group things that look alike

Extra Laws (still useful to recognize)

  • Continuity: We follow continuous lines or patterns

  • Common Fate: We group items moving in the same direction/speed

  • Good Form (Prägnanz): We prefer simple, regular shapes over complex ones

5. Attention: What We Actually Focus On

Your senses might pick up a lot, but attention decides what gets processed at a deeper level.

Types of Attention

  • Selective Attention: Choosing to focus on one thing at a time

  • Divided Attention: Trying to attend to multiple things simultaneously

  • Sustained Attention: Staying focused for extended periods

Problems with Attention

  • Inattentional Blindness: Missing something right in front of you because focus is elsewhere

  • Change Blindness: Failing to notice changes in a visual scene

6. How We Perceive Depth (Visual Cues)

Your brain uses different tricks to see depth and distance — some require both eyes, others just one.

Binocular Cues (two eyes)

  • Retinal Disparity: Slight difference between the two eyes’ images is used to calculate depth

  • Convergence: The closer the object, the more your eyes turn inward

Monocular Cues (one eye is enough)

  • Relative Size: Smaller image = farther away

  • Interposition: One object blocking another looks closer

  • Relative Clarity: Distant objects appear blurrier

  • Texture Gradient: Less detail with distance

  • Linear Perspective: Parallel lines converge at a point

  • Height in Plane: Higher objects in visual field = farther away

Note: Only these specific monocular cues above are tested on the AP exam.

7. Perceptual Constancy: Stability in a Changing Visual World

Even when sensory input changes, we see objects as remaining consistent.

  • Size Constancy: We still see an object as the same size even when it’s farther away

  • Shape Constancy: We know a door is rectangular even when it’s partially open

  • Brightness Constancy: We perceive the same color/shade even in different lighting

8. Perceiving Motion — Even When It’s Not There 🚶‍♂

Movement isn’t always real — sometimes it’s just how our brain interprets it.

Apparent Motion

  • Phi Phenomenon: Lights blinking in sequence look like movement

  • Stroboscopic Motion: Rapid series of still images (like in movies or flipbooks) creates illusion of motion

These illusions are the foundation of animation, GIFs, movies, and other visual media.

Key Takeaways

Perception combines bottom-up sensory data with top-down expectations and experience.

Schemas and perceptual sets are internal influences that create mental filters for interpreting the world.

Context, culture, and past experience are external factors that shape perception.

Gestalt principles explain how we organize visuals into patterns: closure, similarity, proximity, and figure-ground are key.

Attention filters what we process; it has limits, often causing us to miss obvious things (inattentional/change blindness).

Depth cues include binocular (retinal disparity, convergence) and monocular (size, clarity, perspective, etc.) cues.

Perceptual constancies help us maintain stable perceptions despite changes in appearance (size, shape, brightness).

Apparent motion is the illusion of movement, created by visual tricks like phi phenomenon and stroboscopic motion.