Your Brain Responds to a Click Before You Know What It Is

An electrode on the scalp. A click, repeated hundreds of times, every few seconds, for several minutes. The person doesn’t have to do anything. And yet, in the wave the brain draws, there’s something related to their intelligence.

There’s no question to answer.

There’s no button to press.

Just a sound, repeated over and over, and a brain reacting to it without anyone asking it to.

The trick that lets you “see” a clean brain reaction

Psychologist Arthur Jensen devotes a section of The g Factor (1998) to what’s known as the evoked potential, one of the most direct measures that exist of how the brain reacts to a stimulus, with no task or decision involved at all.

The starting problem is that normal brain electrical activity is full of “noise”: random neural activity that makes it hard to detect a clear signal in a single recording.

The solution, borrowed from techniques similar to those used in radar and sonar, is as simple as it is elegant:

• An electrode is placed on the scalp (at the top of the head), with reference electrodes clipped to the earlobes.
• A brief stimulus, like an audible click, is repeated at intervals of a few seconds, over several minutes.
• A computer averages hundreds of fragments of brain activity, each one aligned to the exact instant the click occurred.

What’s random (the background neural “noise”) cancels out when averaged. What’s consistent (the brain’s real reaction to that specific click) stays intact and visible. The result is a clean wave, with characteristic peaks and troughs, reflecting how that particular brain processes a stimulus as simple as a sound.

A wave that “says more” the more complex it is

According to the studies Jensen compiles, including Richard Haier and colleagues (1983), this averaged wave relates to the person’s IQ.

It isn’t that the wave is simply “bigger” or “faster” in higher scorers.

• Some research finds a relationship with the amplitude of certain peaks in the wave.
• Others find a relationship with its complexity: how many distinct dimensions or “shapes” that curve seems to have.
• Jensen’s interpretation is that a more complex wave might reflect more differentiated neural activity, meaning more distinct processes taking part in that reaction, even in response to something as simple as a click.

None of this happens because the person “tries harder” to process the sound. It happens before any effort is even possible: the wave is already there in the first quarter-second after the stimulus, long before any conscious thought about what was just heard.

Why this isn’t the same as an ordinary EEG

It’s worth distinguishing this from another, better-known measure: the spontaneous electroencephalogram (EEG), that “background” brain activity recorded with no specific stimulus at all.

• The spontaneous EEG has also been studied in relation to IQ (the frequency of the so-called alpha wave, for instance), but its correlations are weaker and less consistent.
• The evoked potential, anchored to a precise stimulus repeated hundreds of times, offers a much cleaner signal and, according to Jensen, one more consistently related to g than the spontaneous EEG.

It’s the difference between listening to a conversation among a crowd of people talking at once, or asking a single person to repeat the same sentence hundreds of times and keeping only what repeats identically every time.

What this finding offers (and its limits)

No single click, on its own, reveals anything about a person.

• These are group correlations, obtained from studies with many participants, not a reliable individual measure.
• What matters isn’t the device itself, but what it suggests: that the g factor appears to leave a detectable trace in the brain’s most basic electrical activity, before any recognizable cognitive task even begins.
• Like the rest of the biological correlates Jensen compiles, this doesn’t turn IQ into a fate fixed by a wire and an electrode. It’s one more piece of a much larger puzzle.

What this experiment does leave behind is an idea that’s both uncomfortable and fascinating: part of what makes us who we are, cognitively speaking, can be traced in how our brain reacts to a sound as ordinary as a click, with not even a second of conscious thought involved.

If another equally basic and surprising biological correlate interests you, nearsightedness and intelligence explains a correlation even science can’t fully explain yet.

Sources

• Jensen, A. R. (1998). The g Factor: The Science of Mental Ability. Praeger.
• Haier, R. J., Robinson, D. L., Braden, W., & Williams, D. (1983). Electrical potentials of the cerebral cortex and psychometric intelligence. Personality and Individual Differences, 4, 591-599.