Two letters appear side by side. Decide as fast as you can whether they are the same or different. You'll do two short blocks with two different meanings of "same". At the end you'll see how long your brain needs to retrieve a letter's name.
Based on Posner, M. I., & Mitchell, R. F. (1967). Chronometric analysis of classification. Psychological Review, 74(5), 392–409.
Your results
Analysis options
Name rule: "same" to Aa minus "same" to AA
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"different" to AB: name rule minus shape rule
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Both differences estimate the same thing: the extra time your brain needs to go from what a letter looks like to what it is called. Posner and Mitchell found roughly 70–100 ms. With only a few trials, your own estimate will be noisy, and the two numbers may not agree well. That is exactly why the original study tested a few people on many trials over several days. Change the analysis options above and watch how much your estimate depends on which trials you keep.
How it works. Each block has 34 trials: 4 lead-in trials while you settle into the rule, then 10 of each pair type in random order. Keyboard: A = same, L = different. On a phone or tablet, use the two buttons. By default the analysis drops the lead-in trials, errors, implausibly fast or slow responses (< 200 ms, > 2000 ms), and responses far from the typical RT of their condition: more than 2.5 median absolute deviations (MAD) from the median. The MAD rule is the default because with few trials one slow response inflates the standard deviation so much that a ±2.5 SD rule rarely catches it (Leys et al., 2013, J. Exp. Soc. Psychol., 49, 764–766). Nothing is sent anywhere; your data stay in this browser tab.