You read that headline even though a slice of nearly every letter is missing. Your brain filled the gaps before you noticed there were any. That’s perception, and this lab is about how much of what you “see” your brain is quietly building for you.
About 45 minutes. Part 3 uses your phone’s camera. Your answers save on this device; photos don’t, so screenshot your photo cards before you leave the page.
1
Your brain builds what you see
Sensation brings in raw data. Perception turns it into a story, and your expectations help write that story.
What did you see?
Symbols will flash one at a time. Watch closely and remember the last one.
Ready when you are
What was the last symbol?
12
A
C
14
Read across and it’s a B. Read down and it’s 13. The shape never changed. Only the context did.
Perceptual set: a mental readiness to perceive things one way, created by expectations, context, and recent experience. It’s a kind of top-down processing: your knowledge and expectations shape what the raw input becomes.
Ask a neighbor what they saw. Half the class was shown letters first, half numbers.
Read it out loud
Tap start, read the passage out loud (or whisper it), then tap done. Do both.
Yuor bairn deos not raed evrey lteetr. It gseuses the wrod form its fsrit and lsat ltetres and form waht mkaes snese in the snetncee, so tihs is sitll pssoible to raed qiukcly.
Brof tasel meno dwirp ol fant sorvy kleem. Ap vuttle nis grob plimp cav dorn alt mesh pruve ib ven tolk ratch ib wemmer, ro sunt ik pradgel ot fesh blirtly.
Passage A–
Passage B–
Top-down processing uses what you already know (words, grammar, meaning) to interpret input fast. Passage A had broken data but real words underneath. Bottom-up processing builds a perception piece by piece from the raw input, the way you were forced to sound out passage B letter by letter.
The hidden word
Something is covering parts of a word. Try to read it from the fragments alone, then use the tools below one at a time.
Word 1 of 3
Notice which tool helped more. The hint gave you context, a top-down boost. Showing the cover lets your brain treat the gaps as “something in front” instead of “missing,” so it completes the letters behind it. That’s your brain assuming a whole object continues behind whatever blocks it.
In class: your teacher will play a short audio clip that sounds like two completely different words depending on which one you’re told to listen for. Same sound waves, different perception. Write down which word you heard each time.
Where top-down comes from:schemas (mental frameworks for organizing information), perceptual set, context, expectations, emotions and motivation, and culture. Two people can get identical sensations and perceive different things.
2
Attention is a bottleneck
Your senses take in far more than you can process. Attention decides what makes it through, and what you never consciously notice at all.
Count the bounces
Count how many times the gold dots hit an edge of the box. Ignore the gray dots. It lasts 15 seconds. Focus hard.
Did you notice anything unusual on the screen?
Selective attention is focusing awareness on a limited part of what you sense. The cost is inattentional blindness: failing to see a fully visible object because your attention is elsewhere. In studies built just like this one, a large share of people miss the unexpected object.
Spot the change
The picture flips between two versions with a quick blank in between. One thing is different. Tap “I see it” as soon as you find it.
What changed?
Without the blank, the change jumps out right away. Your visual system detects motion and flicker automatically; the blank hides that signal, so you’re forced to compare from memory.
Change blindness is failing to notice changes in your environment, a form of inattentional blindness. We keep far less detail in memory from moment to moment than it feels like we do.
Your name cuts through
Think of a loud place: the cafeteria, a game, a party. You’re locked into one conversation and can’t follow anything else, until someone across the room says your name and you snap toward it.
Cocktail party effect: the ability to focus on one voice among many while still catching personally important sounds, like your name. It shows unattended input is still being monitored at some level, just not consciously.
3
Your brain organizes and fills gaps
It groups pieces into wholes, turns flat images into depth, and keeps the world stable even when the input keeps changing.
Name the Gestalt principle
Gestalt psychologists argued the whole we perceive is more than the sum of its parts. For each image, pick the principle your brain is using.
Proximity: things close together get grouped. Similarity: things that look alike get grouped. Closure: you fill in gaps to see a complete shape. Figure-ground: you split a scene into an object (figure) and its background (ground).
Depth cue photo hunt
A photo is flat, yet you see depth in it. That depth comes from monocular cues, which work with just one eye. Find each cue in the room or hallway, take a photo, tap the photo to pin where the cue is, and explain it in one sentence. Get at least 3.
Photos stay on your phone and are never uploaded. Screenshot each finished card to submit it.
Two eyes, more depth
Binocular cues need both eyes. Try each one, then check it off.
In the jumping finger test, when did your finger jump more: far or close? Why?
Retinal disparity: each eye gets a slightly different image. The closer the object, the bigger the difference, so the finger jumped more up close. Your brain reads a big disparity as “near.” The hot dog is the two images failing to line up. Convergence: your eyes turn inward more for close objects, and your brain uses that muscle strain as a distance signal.
The world stays steady
Which gray square is lighter?
They’re the exact same gray. Your brain judges lightness relative to what surrounds it, which is what lets a white shirt look white in sunlight and in shadow even though very different amounts of light reach your eye. That stability is lightness (color) constancy.
Now open the door. Watch the shape it makes.
The image on your retina becomes a narrower and narrower trapezoid, but you never think the door is changing shape. That’s shape constancy. A friend walking away down the hallway casts a smaller and smaller image too, yet you don’t think they’re shrinking: size constancy.
Perceptual constancy: perceiving objects as unchanging in size, shape, and lightness even as the image reaching your eyes changes.
Make motion that isn’t there
Two dots take turns blinking. Neither one moves. Slide the speed until the two blinking dots turn into one dot sliding back and forth.
Apparent motion (the phi phenomenon): perceiving movement when stationary lights flash in quick succession. It’s why arrow signs seem to “run,” and the same idea behind movies and animation: separate still frames perceived as continuous motion.
4
Apply it like the AP exam
The exam won’t ask you to define these. It will hand you a scenario and ask you to apply them.
Scenario practice
Exit ticket
Dev is walking through a crowded hallway between classes, scrolling on his phone. He walks right past a coach holding up a huge sign about tryouts and never notices it. But when someone behind him says “Dev,” he looks up immediately. Down at the far end of the hall, he spots his friend Maya. She makes a tiny image on his retina, but he knows she’s normal-sized and just far away.
Submit your lab
Your PDF includes your name, every written answer, your results from each station, and your depth cue photos with pins.
Walk out with these three
Perception is built, not recorded.Bottom-up processing starts with raw input; top-down processing uses schemas, perceptual set, context, expectations, and culture to interpret it.
Attention is a bottleneck.Selective attention lets you focus, with costs: inattentional blindness and change blindness. The cocktail party effect shows unattended input is still monitored.
Your brain organizes and fills gaps.Gestalt principles group parts into wholes; monocular and binocular cues create depth; constancy keeps the world stable; apparent motion creates movement from stillness.