A Thrifty Brain gave us Multi-tasking Abilities

Unlike a computer, which would recruit multiple “cores” to multitask, the brain has to use a pretty sophisticated workaround to multi-task. And it all comes down to how the brain allocates limited “reserved” resources to perform a task and how it compartmentalizes and prioritizes small units of information efficiently.

We have only 1 attention system. This system’s main job is to select a few stimuli that are competing with each other and bring only a few into our awareness at a time. So, we can focus on 1 thing at a time. But we can switch our attention to other things without losing the reference to the previous thing by storing information in our working memory. It’s like a very limited fast-acting ultra-short-term cache. Our everyday attention-system really is a partnership between attention and working memory. Neither are powerful enough by themselves.

Working memory – the space in which multi-tasking happens

Working memory has compartments^[1] that hold information of different kinds. Sound information, visual information, information pulled from long-term memory. This captures multiple facets of what you pay attention to. This compartment allows the brain to simultaneously keep multiple things on standby, and then focus on 1 of them as needed without losing track of other things.

It could remember the sounds and people in a cafe while working (current context). But it could simultaneously also store the movie dialogs and a future plan you are making with friends (relevant but not the current context). All because the information can be broken down into its components and stored in those compartments.

Let’s call them tasks or threads. E.g. shopping, talking to your partner, and calculating your overall expenses are all different threads. These are your top priorities which have gotten the privilege of your attention system.

Limited capacity – how the brain optimizes it

A general capacity of this working memory is 4 units of information^[2]. This can change a lot depending on how much a person trains to remember something specific. E.g., a historian would easily remember a large sequence of historical events. A programmer could remember a large flow of functions. This domain expansion occurs because of the schema – a large web of patterned information that we develop when we learn something deeply.

Depending on the load, the brain will invoke additional resources, like from a circuit called “multiple demand network”. This network is good at handling complex cognition that needs to prioritize many different things and quickly switch attention. Everything from the first few lessons in a new language to solving a big coding problem or even redesigning a house will use this mode of the brain. It will essentially gather and offer priority access to memory and our “processing” system called “executive functions”, which do the planning & decision-making.

A very unique property of our working memory is that we can compress items in it to fit more. Just like a zip file compresses files on a computer using patterns in data, humans compress information by finding patterns in it^[3]. Chunking is the most common way to compress this data. E.g., a person can remember 20 grocery items if they group (chunk) them together, but recalling a list of 20 items in order will be very difficult. Similarly, those schemas improve the compression.

This compression system really makes a lot space in working memory for the brain to accommodate more tasks.

The total burden of work the brain has to do is called “cognitive load“. Low cognitive load means there is very little space occupied by attention in our working memory or the information is really compressed well because a person is familiar with it or an expert at it. For example, folding clothes while humming a song is low cognitive load, but solving sudoku while listening all animals in alphabetical order would be high cognitive load.

Tip: (designers often try to reduce cognitive load in a visual design so it is easy to follow but educators try to keep it moderate so the brain undergoes purposeful processing that improves learning).

Maximum cognitive load would mean you are at the limit of your working memory and your attention or memory can’t keep up with the task’s requirements. Fatigue sets in at that point and we need to recover and replenish our attention by taking a break or engaging in unrelated light, fun activities.

So far, we’ve had attention being expanded by working memory and information in working memory being compressed to create more space. But now that we have more space, how does the brain actually do the “multi” tasking?

Cognitive flexibility – how we switch tasks

We also have a core cognitive feature called cognitive flexibility which allows us to switch threads and return to a task. It is a top-level “selector” that brings some group of information into awareness while de-prioritizing something else. It excels at changing priorities and keeping things on standby for future use. Like pausing brain-storming discussion to answer your boss.

This one is a very, very important cognitive feature of the brain. It is essentially responsible for us to quickly understand the context and switch between conversations or tasks. For example, you can have a conversation about a travel plan with a friend on WhatsApp and still continue tomfoolery on Instagram at the same time. You can then pause all of that to respond to a LinkedIn job application too. All thanks to cognitive flexibility. It is one of the core “executive functions” enabled by the frontal lobe of the brain that handles decision-making, thinking, planning, and problem-solving.

And then, if a task is very familiar, it’ll rely on automatic resources. We call them habits. Like walking and talking. It doesn’t need your attention unless something dramatic happens. A habit is a way for the brain to optimize the resources needed to do a task. Your brain will literally use fewer resources.

Attention – How it prioritizes

Research shows^[4] that novel tasks engages the brain’s executive functions a lot but the first time but once a person is familiar with it, the executive functions are less used and the brain relies on past (or new) learning to complete the task. An expert, would do a complex thing habitually because the solutions have been automated and optimized through practice. Such a task would need very few mental resources. So, the brain is now free-ed up to use its executive functions to tackle more and new information, like multi-tasking or dealing in a really odd problem. This is also why our brain ends up mind-wandering when it is doing a highly automated task – the freed-up spaces gets occupied by default activity (unsurprisingly called the “Default Mode Activity”). That activity often leads to random thoughts, odd creative ideas, or unexpected anxiety.

This optimization occurs for both mental^[5] and motor skills^[6]. So mental math, speaking fluently, or throwing darts. But not all everyday tasks require one thinking task and one automatic task. Sometimes, it is 2 automatic tasks like cleaning and singing a familiar song. Or it is 2 or more cognitive tasks like studying for Math and English.

In either case, the brain is equipped to handle many inputs of information. Let’s look at the case of being safe on the road. Your automatic task is walking and pausing at the right spots. Your cognitive task is evaluating when and how you should cross the street.

Now imagine, suddenly, you hear a loud honking. You can’t spot where it is. You were not expecting it either. How does your brain know it?

For this, our attention has evolved to be purposeful and simultaneously vigilant by having 2 different attention systems – one for you to control (endogenous attention) and one for outside stimuli to capture^[7] (exogenous attention). The endogenous attention component is purposeful. You’ll focus on your task. But the exogenous attention will stay vigilant and capture distracting details. Like someone calling out your name or a loud siren going off. The priority quickly changes when both these attention systems get triggered simultaneously. Still, the brain won’t always forget the things it was just paying attention to. Thanks to that working memory. You won’t forget where you were walking or what you had to do.

But… sometimes we do forget. A loud, distracting sound can make us forget what we were doing. One of the main reasons this happens is that the working memory is already full. For example, in the 3 components of the working memory we looked at (auditory, visual, and episodic buffer), the auditory component could be full of information. Then, the loud noise could put a lot of strain on its capacity and make you temporarily forget what it already had, simply because the loud noise is given more priority.

All of this wet dynamic, seemingly unstable machinery works together to allow the brain to multi-task, switch tasks, and handle many inputs and still make decisions.

Our cognitive architecture is quite beautiful!

If the brain CAN multi-task, why not do it?

So far we know 2 things (explained above) – we have attention that gets occupied by a task and we also have space remaining for another task in our working memory. Because of these 2 things, we can multi-task in a productive way… as long as we don’t reach the limits of our working memory (like overloading the visual compartment or relying too much on long-term memory that you start fatiguing).

We can listen to familiar music while working on a relatively boring task and actually improve efficiency. We can also do 2 relatively light tasks simultaneously to stay stimulated and avoid boredom. But because we have a limited bandwidth, it gets hard to multi-task during complex activities. Or, conversely, multi-tasking while doing a complex task tends to make us less efficient at it. I’ve explained this situation more here.

But, we can conclude the following:

• Automatic task + moderately complex task –> Ok
  E.g., Familiar music + homework
• Complex task 1 + complex task 2 –> Inefficiency, Not Ok
  E.g., Coding + recording music
• Easy task 1 + Easy task 2 –> Ok
  E.g., Chatting + reading news

However, there are some people who can multitask^[8] even when things get very difficult because their brains can direct their attention system to 2 simultaneous places with ease. They are generally better at multi-tasking than most, just like how some people are taller or more flexible than most others.

So, saying the brain can only focus on 1 thing is a gross oversimplification. You’ll see that, even without being one of the rare dual-attention people, the brain is capable of managing a lot of information at a time.

Visual summary

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