Lab Talk

flexibility and forgetting

For Cognitive Flexibility, Forget the Past

Being flexible in our approach to the future often requires the ability to inhibit or forget the past.

In 1942, Abraham Luchins published a seminal experiment called the “Water Jug Problem”. In this experiment he asked his participants to answer a series of numerical problems where they had to define an equation based on the capacity of each jug that delivered the desired quantity.

The problem could be solved using one solution, or sometimes both the first solution and an alternative simpler one.

The experiment was designed in a particular way to explore how their experience of solving the initial problems using a specific formula, prevented them from realizing that the latter ones could be solved using a different, more efficient approach.

See the problems he set below:

Problem Capacity of Jug A Capacity of Jug B Capacity of Jug C Desired Quantity
1 21 127 3 100
2 14 163 25 99
3 18 43 10 5
4 9 42 6 21
5 20 59 4


6 23 49



7 15 39



8 28 76 3


9 18 48 4 22
10 14 36 8 6

All problems except 8 can be solved by B – 2C – A and for problems 1 through 5 this solution is simplest. However, for problem 7 and 9 the simpler solution is A + C and problem 8 cannot be solved by B – 2C – A, but can be solved by A – C. Problems 6 and 10 can be solved more simply as A – C. as well as the more complex formula of B – 2C – A.


Choosing the simplest solution?

He had two experimental groups. In the first group, the participants answered all problems in order, whilst in the second group, they were only given the last 5 problems. The idea was that the first 5 problems which were all solved by the B – 2C – A would interfere with their ability to answer the later problems.  In other words, that their “familiar” routes of thinking and problem solving would block, or inhibit, their ability to use a more novel approach to solve the problems which was more efficient.

And this is exactly what he found. In the first group of participants 83% of participants used B- 2C – A on problems 6 and 7 and 79% used B – 2C – A on problems 9 and 10 (compared to ~1% in group 2) instead of choosing to use the simpler solution. In addition, 64% completely failed to solve problem 8 (compared to 5% in group 2) which could be solved by a relatively simplistic formula but not the familiar B- 2C – A one used in the first five problems.

When good thoughts blocks better ones.

And so arose the “Einstellung Effect” – the situation where our familiar thoughts, our mental roads well traveled, block, or inhibit, our ability to generate novel solutions and ideas. Stopping us being flexible in our thinking, encouraging us to stay with the status quo and introducing a degree of rigidity in our thinking where we steadfastly stand by what we know and think, often blind to other possibilities or alternatives. And like many “biases” in our thinking, it happens without us even realizing. Infiltrating our attentional systems to ensure that we only pay attention to the information which reinforces the familiar road of thinking, whilst ignoring any information which might be trying to convince us otherwise.

The Einstellung effect is one example where our learned experience can actually (unhelpfully) inhibit our ability to select the best behavioral outcome, something shown by researchers such as Merim Bilalić from Oxford University, and where “forgetting” can be beneficial.  For example, another study from researchers at the University of California showed that participants who were better at “forgetting” recent distracting information (in this case, ideas provided by the experimenter), were actually able to generate more novel ideas on a divergent thinking creativity task.

 Regretful thinking and fear inhibit flexibility

There are also other examples of how our inability to “let go of the past” prevents us from being flexible and forward thinking. Take the example of regret, a feeling which, like fear, can prevent us from choosing the optimal action to take, and causes us to “shut down”, paralyzed by the fear of making the wrong decision based on recollected unpleasant outcomes of our past choices.

Classical studies of fear conditioning and extinction have identified a framework within which individuals can re-program their memories according to what is still to be feared, and what is no longer fearful, something that enables them to update and adjust their behavior within a changing environment.

As humans, our tendency to overanalyze the past and speculate on the future, something that activates similar brain networks, means that we require more sophisticated cognitive mechanisms such as counterfactual thinking, the generation of alternate ‘what if’ scenarios to overcome these tendencies, and use our experience as a strategy for future change, rather than an excuse for inaction.

Measuring flexibility in the brain with EEG

Can we measure how the brain handles this flexibility using EEG?   This is no simple task.  However researchers have made a start. Researchers from Justus-Liebig University Giessen and Harvard Medical School (Mueller et al) measured  EEG activity when participants underwent a 2-day conditioning and extinction paradigm. They found that the recall of extinguished fear conditioned stimuli was associated with changes in gamma (~36.5–44 Hz) activity across ventromedial prefrontal sites whilst, recall of non-extinguished fear conditioned stimuli was associated with changes in theta (~4–8 Hz) activity across anterior mid cingulate cortical sites.  Thus the nature of association between the stimulus and fear is apparent in aspects of the dynamical outcome.

Staying flexible

Cognitive flexibility is our ability to update, inhibit and overcome learned neural pathways to ensure that we are capable of adapting to our diverse and ever changing physical, technological and social environment.

How much should we forget? What should we inhibit?  If are able to measure our cognitive flexibility perhaps we will understand better how to evolve our minds more efficiently for our ever changing world.



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