# Stroop Effect Experiment for the Classroom, Timed on Phones Source: https://decka.dev/classroom/psychology/stroop-effect Every student times four index cards on their own phone, out loud: name the ink of coloured blocks, then of colour words printed in clashing inks, then read the words of two more cards. The big screen lays the room's times on a till receipt and sets each student against themselves. ## What it teaches Students measure the Stroop effect on their own voices: how much clashing colour words slow down naming the ink, and how little the ink slows down reading the words. Through that asymmetry they meet automaticity and interference. They see why subtracting each person's own times cancels out who is quickest, and why the cards' order works against each claim: A before B and D before C, so practice helped B and C. ## The Stroop effect, run on the room's own voices Four index cards lie face down on the big screen. Card A is coloured blocks and card B is colour words printed in clashing inks: on both, the room names the ink. Card D is another clashing card and card C is plain black words: on both, the room reads the words. Each student times each card on their own phone. They tap Start, the card appears, they say every item out loud, left to right, row by row, and tap Done. The card shows only while their own clock runs, and nothing on the phone counts or moves. Before sending, they say how many they said wrong or had to fix. When card B closes, it is laid large on the big screen and the room names its inks together, out loud. Then both cards' times land on a till receipt, one notch per person in one-second columns: card A's above the receipt and card B's below it, each card's middle inked through its pile. Next a second strip is laid under the receipt, its zero under card A's middle, and each person's own difference, card B minus card A, drops onto it. Zero is inked first, so the room sees which side every mark lands on, and the strip counts each side. After the room reads card D together, the reading differences, card D minus card C, land on the same strip under the naming pile. In most rooms they sit close to zero, and the board says so whichever way they fall. The two middles then stand side by side: words cost the room seconds when it names the ink, and the ink costs it almost nothing when it reads the words. Reading has become automatic for the room, and naming a colour has not. The screen shows counts only: no names, no ranking, no fastest time. Each phone shows its owner's own times and differences beside the room's middles, and which column their own mark is in. A student who finds some colours hard to tell apart can sit a colour card out, and anyone can say they couldn't do a card; both are counted apart, never as missing, and nobody sees who. Try the screen-and-phone preview, where the phone is yours to time and fictional classmates answer through the same runtime as the lesson. ## Classroom debrief On card B, did everyone slow down, or just most of us? What would it take for someone to land left of zero? Card B and card D were built the same way. Why did the words get in the way of naming, but the ink hardly got in the way of reading? The order was A before B and D before C, so practice helped B and C. How would doing card B first have changed the naming result, and why does helping C make the reading result harder to keep near zero? Did anyone go faster on card B by making more mistakes? How would you score speed and accuracy together? Where outside this room does a habit you can't switch off get in the way of a deliberate task? ## Stroop effect experiment questions, answered ### What do I need besides phones? Only a projector or big screen. Each phone shows its own copy of each card while its student times it, so there is nothing to print or hand out. The whole room says the colours out loud at once, so expect noise: everyone is timed in the same noise. ### What about students who find some colours hard to tell apart? Every colour card offers “I can't tell some of these colours apart”. A student who taps it sits that card out and is counted as “sat out: colours”, never as missing, and nobody, on the screen or on another phone, sees who. The four inks were checked against simulations of the common kinds of colour blindness, and the sit-out is there for anyone they still fail. Card C is printed in black, so everyone reads it. ### Is it fair to students who read slowly, or have dyslexia? Yes. Someone who reads slowly is slow on cards D and C alike, and someone who names colours slowly is slow on cards A and B alike, so subtracting each student's own times leaves what the clashing words cost them, not how fast they read. Anyone can tap “I couldn't do this one” on any card; it is counted apart, never as missing. ### Why coloured blocks rather than colour words in matching inks? A word printed in its own colour can be read instead of named, so the gap between it and a clashing card would mix reading speed with interference. Blocks keep the task the same, naming an ink, and add only the words. ### Why does the screen never show names? Every mark on the screen is one person, but none says whose: the screen counts, it never ranks. Each phone shows its owner's own times beside the room's middle and says which column their mark is in, so a student can find themselves without anyone else finding them. ### Does a slow phone change the result? A touchscreen adds a short delay to Start and to Done, but the same delay to both cards a student compares, so it drops out of their difference. That difference, person by person, is the lesson's answer. ### What if a student is interrupted? Before sending, a student can say “Something interrupted me” and take the card once more. That second take is counted as a retake, because they have seen the card. ### How long does it take? Four timed cards, two choruses and three reveals; the saved default shows under the headline as "About N min", and every timer is a setting you control before you run it. ## Run the lesson Present the boards in PowerPoint and Decka. Students scan a QR code or open the session link to join from their phone browsers.