The neurological basis of intuition

Most of us have experienced the vague feeling of knowing something without having any memory of learning it. This phenomenon is commonly known as a "gut feeling" or "intuition"; more accurately though, it is described as implicit or unconscious recognition memory, to reflect the fact that it arises from information that was not attended to, but which is processed, and can subsequently be retrieved, without ever entering into conscious awareness.

According to a new study, our gut feelings can enhance the retrieval of explicitly encoded memories - those memories which we encode actively - and therefore lead to improved accuracy in simple decisions. The study, which is published online in Nature Neuroscience, also provides evidence that the retrieval of explicit and implicit memories involves distinct neural substrates and mechanisms.

The distinction between explicit and implicit memory has been recognized for centuries. We know, from studies of amnesic patients carried out since the 1950s, that implicit memories can influence behaviour, because such patients can learn to perform new motor skills despite having severe deficits in other forms of memory. Thus, the term implicit memory refers to the phenomenon whereby previous experience, of which one is not consciously aware, can aid performance on specific tasks.

Ken Paller of Northwestern University and Joe Voss, who is now at the University of Urbana-Champaign in Illinois, set out to investigate further the influence of implicit recognition on decision-making, and used electroencephalography (EEG) to try to identify the brain activity associated with it.

12 healthy participants were presented with kaleidoscopic images under two different conditions. In one set of trials, they paid full attention to the images, and then perform what is referred to as a forced-choice recognition test, in which they were shown another set of images and asked to decide whether or not they had seen each of them before. In the other condition, they were made to perform a working memory task whilst the initial first set of images were presented to them - they heard a spoken number and were asked to keep it in mind, so that during the next trial they could indicate whether it was even or odd. Thus, in these trials, their attention was diverted away from the stimuli.

Thus, under the first condition, the participants are consciously aware of having seen some of the images before, and had formed explicit memories of the presented images. During the forced-choice test, they could base their decisions on these memories, and report afterwards that they remembered or knew whether or not they had seen each image before.

By contrast, during the diverted memory trials, they did not form explicit memories of the stimuli, and under these conditions reported either that they had guessed at the answer. This therefore signifies that the participants were unaware of any memories of the images presented to them.

Nevertheless, the decisions which were reportedly made by guessing were found to be significantly more accurate than those based on explicit memories of the visual stimuli,. This suggests that visual information can be encoded accurately even when one is not paying attention to it -something which has been demonstrated before -  and also leads to the counterintuitive conclusion that retrieval of a memory is actually enhanced one's attention is diverted during encoding of that memory. 


The researchers measured event-related potentials as the participants performed these tasks - that is, they used an elastic cap, containing 59 electrodes evenly distributed over the scalp, to measure the electrical activity of the brain. This showed that each type of decision - those based on explicit and implicit memory - was associated with a distinct spatio-temporal pattern of brain waves (above). During trials in which decisions were based on explicit memories, bursts of activity were recorded from one cluster electrodes, beginning approximately 400 milliseconds after the onset of the stimuli.

By contrast, trials involving implicit memory (during which the participants' attention was divided) were associated instead with a decrease in activity recorded from another electrode cluster, which began at around 200 ms after the stimulus onset.   

That distinct electrophysiological signatures were associated with explicit and implicit memories suggests that the retrieval of each involves distinct neural mechanisms - retrieval of the former was associated with reduced activity in the occipital lobes and left prefrontal cortex. One would therefore predict that implicit memory retrieval can be disrupted by perturbing activity in those parts of the brain, and this could be tested to confirm these findings, perhaps by using transcranial magnetic stimulation. Future work may also identify the specific occipital and prefrontal areas involved.

This study, then, suggests that when we try to remember something, we actually know more than we think we know,  because of implicit memory recall of which we are unaware, and that  what we call intuition may in fact play a large role in decision-making.  

Voss, J. L. & Paller, K. A. (2009). An electrophysiological signature of unconscious recognition memory. Nat. Neurosci. DOI: 10.1038/nn.2260.

Schacter, D.L. (1987). Implicit memory: history and current status. J. Exp. Psychol. Learn. Mem. Cogn. 13: 501-518. [PDF]

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Aha! I just wrote a book about unconscious decision making... Too bad this research came out after the book was published! I may have to refer to it in a newer version.

Great article. Thanks for bringing this research to our attention.

Nice post, because "intuition" is gaining momentum and is recieving too much attention in many fields actually: experimental philosophy, cognitive psychology...

This study in particular substantiate neurally one apsect of what J. F.Kihlstrom called the "cognitive unconscious": unconscious systems that operate beyond volitional control but with all cognitive characteristics of conscious information processing.

Kihlstrom 1987

From article above:

"(T)rials involving implicit memory were associated instead with a decrease in (neural)activity." So they conclude, "retrieval of each involves distinct neural mechanisms."

Of course, they're overlooking one important possibility that is probably difficult for them to imagine -- maybe intuition is not a neural mechanism at all.

Explicit memory showed increased neural activity in particular regions, but people asked to guess or use intuition showed decreased neural activity. Could there be a reason we call it a "gut feeling?"

They actually show no evidence of the information originating in any neural activity. What other options might be worth consideration?

By Artemystic (not verified) on 10 Feb 2009 #permalink

This is in line with several other studies about the subconscious and decision making. One in particular - which focused on the the decision of which car to purchase, conducted at the University of Amsterdam - almost parallels this study. The results there also suggested that we make better decisions "subconsciously" or intuitively. Good for companies to know as they shape products and services for customers.

Thanks! This reinforces what I keep telling my clients - sometimes things sound strange and 'New-Agey' but it is only because we have yet to understand the science behind it.

Great discussion -- permit me. #1 The mass of neurons in the gut is said to be equivalent to the mass in the head. If anyone suggested all the mass in the head was necessary to move my hand, and served no other function people would laugh -- . #2 It feels to me the brain is very good at close intellectual examination, and the gut more the master of impression and correlation, taking visual cues, sensory impressions, body signals, hormonal messages and ending with an immediately available this or that conclusion in the form of an over all " gut feeling ". #3 The GUT feeling would seem a helpful attribute for survival, many important reactive decisions would be useless if the brain took it's time in giving a result. #4 Brain and gut look like 2 different software programs, intellectuals seem to favor the brain's work, the religious and right wing seem to favor the gut's conclusions. #5 Can't agree that the " best " decisions are the subconscious ones, my gut keeps telling me the best car for myself is the Ferrari -- and I would be SO in jail......

By greg zurbay (not verified) on 10 Feb 2009 #permalink

Thanks for this! Can anyone provide a real-world example of when this research would be applicable, e.g., when an implicit memory would be formed? Is it akin to driving down a road, in conversation, but somehow knowing where a particular business is along that road, without having made an effort to commit it to memory?

Another study seems to add a similar data point:

Here, people listening to an audio clip who coloured in shapes (*) could recall more of the content from the clip than those who just listened.

(*) Unlike the project author, I refuse to call that "doodling"; as a lifetime doodler, I would stick to "colouring" as a description

By Desirée (not verified) on 01 Mar 2009 #permalink

This is key stuff, showing that the Unconscious Mind can encode memories and produce "intuitive" recall entirely without the Conscious Mind being involved. In fact, this seems to prove that "interference" by the Conscious Mind may hamper recall!

The Conscious Mind may well alter the immediate recall due to its own rational(izing) needs... or there may yet be other issues in play (e.g. uncertainty introduced when the Unconscious Mind feels "scrutinized").

Please don't forget that this is very preliminary and only slightly more sophisticated than phrenology. we still are not fully aware of which of more activity or less activity is the more significant. less activity could be a more significant signal that the reverse.

And gut feelings and intuition also relate to the ugly world - the world of racism, stereotyping and seeing other people as different. However this does point to the great difficulty of changing those intuitively held, gut feelings because they are not completely subject to conscious volition.