Try reading the following sentences : ”He took a sip from the transmitter.” – “I take coffee with cream and dog.” – “He planted string beans in his car.” Did you experience anything unusual? Probably not, but if you had been hooked up to a set of scalp-electrodes and an electroencephalographic analyser which was recording the electrical activity of your brain, the system might well have logged an N400 event.
The N400 wave (so-called because it’s a negative-going pulse which appears around 400ms after the stimulus) was first described in a 1980 paper for the flagship journal Science : Kutas, M., & Hillyard, S. A. (1980). Reading senseless sentences: Brain potentials reflect semantic incongruity.
Lab-based investigations had demonstrated that when experimental subjects read an ‘incongruous’ sentence like the examples above the enigmatic N400 signal consistently showed up.
Since its discovery, a swathe of scientific papers (more than a thousand in fact) have attempted to refine, understand, and utilize what some researchers have dubbed the “Incongruity Wave” – in a host of imaginative ways.
As a recent example, see this 2011 paper, from a joint Spanish/German research group which attempted to quantify the ‘counterintuitiveness’ levels in various sentences that were either deemed ‘religious’ in nature, or not. The team showed various sets of sentences to experimental participants, e.g.
[Counterintuitive religious] “From his beard came out asteroids.”
[Counterintuitive non-religious] “From his beard came out wardrobes.”
[Intuitive] “From his beard came out gray hairs.”
The N400 data from the experiments showed, say the investigators, that : “… religious ideas appear as less semantically anomalous for the human cognitive system than other types of world-knowledge violations.”
Intriguing though the results might be, readers should bear in mind that the exact nature of the N400 and any possible implications it might or might not have are still quite a way from being fully understood.
Note: The graph shown above, from the original 1980 paper, displays the N400 as an upward rising peak following the sentence “He spread the warm bread with socks.” Unusually perhaps for a graph depicting electrical activity, the Y axis shows negative voltage swings above the zero line rather than below.
Further reading :
‘Thirty Years and Counting: Finding Meaning in the N400 Component of the Event-Related Brain Potential (ERP)’
Laughter and electroencephalographic activity* and
Humor appreciation as an adaptive esthetic emotion