A Cognitive Psychology Lab in 30 Minutes: Replicating Classic Experiments with Reaction Time, Stroop, Digit Span, Mental Rotation, Trail Making, Tower Planning, and N-back

The most frustrating moment in a cognitive psychology course is when the textbook's classic experiments are only read about. The seven tasks bundled here each take two to five minutes, run in the browser, and show their classic effect right in the class's anonymous distribution. Pick two or three per session. For each task there is one set: what it measures, which number from which paper, and what to look for in your class distribution. The running procedure is shared, so it appears once at the end.

1. Stroop — automaticity and interference

Naming the ink color of the word RED printed in blue is slow. Stroop's (1935) original experiment showed the delay with color words printed in mismatching ink, and MacLeod's (1991) review of half a century of research confirmed it as one of the most reliably replicated effects in psychology. The class measure is interference = incongruent reaction time − congruent reaction time. The fact that nearly everyone in your class distribution sits above zero is itself the evidence that reading is an automatic process you cannot switch off. For the mechanism in depth, pair this with the site's Stroop effect guide.

2. Digit span — 7±2 or 4?

Read out digit strings that get longer and ask students to repeat them; somewhere it breaks down. Miller (1956) called the limit 'the magical number seven, plus or minus two'; Cowan (2001) recomputed the true capacity as about four items once rehearsal and chunking are prevented. See where your class median falls between Miller's 7 and Cowan's 4 — a digit-span task allows rehearsal, so it usually comes out above Cowan, and that gap is the starting point for discussing how measurement conditions change capacity. Activity: read a phone number chunked 3-4-4 and test how much the span grows.

3. Mental rotation — the time it takes to turn an object in your head

Students judge whether two shapes are the same object (merely rotated). Shepard & Metzler's (1971) finding was that reaction time rises linearly with the angle of rotation — at roughly 60 degrees per second, as if the object were actually being turned in the mind. The paper launched the debate over whether mental images are picture-like representations. In your class, plotting mean reaction time by angle reproduces the line. Discussion hook: why can't the brain answer 'all at once' instead of spending time in proportion to the angle?

4. Trail Making — norms and age

A neuropsychological test in two parts: A connects numbers in order, B alternates numbers and letters. Reitan (1958) established it as an indicator of brain damage, and Tombaugh (2004) published norms from 911 people aged 18–89, stratified into 11 age groups and 2 education levels, showing times lengthen with age and with less education. The class measure is B − A (switching cost). A same-age classroom cannot show the age effect, which makes it a good place to teach why norms are stratified by age and education — compare students' times with Tombaugh's norms for their twenties.

5. Tower planning — planning ahead

The Tower of London: move beads to a target arrangement in the fewest moves. Shallice (1982) adapted it from the Tower of Hanoi and showed a specific planning deficit in patients with frontal-lobe lesions, evidence that underpins the concept of executive function. Class measures: moves beyond the minimum, and the time spent thinking before the first move. When your class splits into 'thought long, moved little' and 'moved at once, backtracked a lot', that is individual difference in planning strategy.

6. N-back — same name, different thing

Students say whether the current item matches the one n steps back; Kirchner (1958) introduced it. Jaeggi et al. (2008) reported that N-back training raised fluid intelligence, fueling the 'brain training' wave, but Redick & Lindsey's (2013) meta-analysis (20 studies, 2,178 participants) found the correlation between N-back and complex span tasks to be only r = .20 — both called 'working memory', yet sharing just 4% of their variance. In class, put the digit-span and N-back distributions side by side and ask whether the same student lands in the same place on both. One task that teaches 'same name ≠ same construct' and the replication debate at once.

7. Reaction time — the pitfalls of the simplest measure

Press as fast as you can when the signal appears — simple reaction time. Conceptually the simplest, yet the task with the most to teach: the same person's values scatter across trials (within-person variability), absolute values differ by device and browser, and you have to decide what to do with premature presses (anticipations). In your class distribution, look at the fastest trial and the median rather than the mean, and discuss why reaction-time research so often uses medians or trimmed means. It is the foundation for reading the reaction-time measures in the other six tasks.

Shared procedure (10 minutes per task)

1. Before class: create one group link per task ('Create a group link' on the test page) and collect the links (or QR codes) on one slide. No sign-in needed.
2. Predict, 1 min: after explaining the task, have students write a prediction of their own result ('Will my interference be above zero?', 'How many digits will I hold?'). The gap between prediction and result is the best discussion material.
3. Test, 2–5 min: quietly, notifications off, same posture. For reaction-time tasks, comparisons are fairest within the same device type.
4. Distribution, 2 min: put the group hub's anonymous histogram on screen and check the 'what to look for' noted above. Keep the rule that nobody announces their own position.
5. Discuss, 2 min: one discussion hook for that task. If time remains, ask 'if someone did not show the effect, why might that be?' — practice in separating measurement error, strategy, and device issues.

• 🎨Stroop testInhibition under color-word interference.Take the test →
• 🔢Digit spanShort-term memory span for digits.Take the test →
• 🔄Mental rotationSame shape or mirrored? Rotate it in your head.Take the test →
• 🔗Trail makingConnect in order, fast — processing speed.Take the test →
• 🗼Tower planningPlan the minimum moves to build the tower.Take the test →
• 🔁N-back (2-back)Working-memory updating.Take the test →
• ⚡Reaction timePure speed of response.Take the test →
• 🟦Spatial span (Corsi)Spatial working memory for locations.Take the test →