Semantic Priming

What it is

The paradigm is minimal. Show a word, then show a string of letters, and ask the person to decide as fast as they can whether the second is a real word. If the two are related in meaning, the decision is faster. The difference is measured in milliseconds.

David Meyer and Roger Schvaneveldt established it in 1971. The standard explanation is spreading activation: recognising a word raises the readiness of concepts connected to it, so a related word arrives at an already partly primed representation.

What makes the effect durable is the design rather than its size. Each participant contributes hundreds of trials, so each person acts as their own control and the between-person variability that swamps small effects is removed by construction. The effect is not large. It is measured with enough precision that it does not need to be.

In effect

The Semantic Priming Project measured it at scale: 768 subjects, 1,661 target words, four prime types at two intervals. Lexical-decision priming ran at roughly 19 ms and was stable across a long session, which is not what a fragile effect looks like. First-associate priming ran at 26 ms at the shorter interval.

It has since been confirmed in a Registered Report across nineteen languages with more than 25,000 analysed participants, with the design and analysis accepted before any data were collected. Very few effects in psychology have been tested that way, and fewer have survived it.

The honest caveats sit at the item level rather than the group level. Split-half reliability for individual word pairs is low, so the group effect is rock solid while any particular pair's estimate is noisy. And masked or subliminal semantic priming, where the prime is presented too briefly to be consciously seen, is much weaker than the standard version, with part of the apparent effect attributable to stimulus-response mapping from repeated primes rather than to meaning.

What it does not say

It says nothing about behaviour. Recognising a word faster is not walking more slowly, judging a stranger as warmer, or wanting soap.

The two literatures share a word and almost nothing else. Semantic priming is measured within subjects, in milliseconds, across hundreds of trials. Social priming was almost always measured once per person, between subjects, on an outcome with far more variance. That difference in design predicts the difference in replication record without any appeal to the content of the primes.

David Meyer, who co-authored the founding paper, made the distinction himself in a letter to Science in 2014: some priming effects are real and easily replicable, the failures concern the more exotic behavioural claims, and popular authors touting the latter should treat them with caution. His footnotes named Blink and Thinking, Fast and Slow.

Letting this paradigm's security transfer to the other is exactly the move a reader should refuse.

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