In recent years, strategies drawn from cognitive science have become essentials in many teachers’ classroom toolkits. These strategies have a variety of implications for practice but many of them originate from a single fundamental idea: that the human brain is a system of finite resources, with only a limited capacity for processing information. 

From this idea of limited capacity comes the belief that we can impose a “load” on our processing systems. That load, the thinking goes, can be too little, too great, or in the “Goldilocks” zone: just right. In academic literature, these ideas about limited capacity and its effects are termed “load theories”.

The educational implications of limited capacity have been widely debated, but what there has been far less discussion about is the fact that there are actually a number of different bottlenecks in the human processing stream. So, there is more than one single “load” theory, and each has its own implications for how we learn. 

Before we get too far into our discussions of load, then, it might be worth clarifying what we are really referring to.

Cognitive science: perceptual load

The first process in which capacity limitations affect our ability to process information is attention. Our ability to attend to any of the huge range of stimuli present in our environment at any one time is actually surprisingly limited, and relatively fixed.

In experiments, finding a target, such as the letter “X” from a display of six letters, can be enough to seemingly exhaust our attentional capacity.

We can see whether capacity has been reached by measuring whether or not other stimuli that are not related to the task (distractors) affect people’s performance in searching for the target letter. 

At high levels of perceptual load, the effect of the distractor is significantly reduced, causing almost no slowing down of the response at all. At lower levels of perceptual load, the distractor is processed to a much greater degree, and so causes a larger impairment. This is because, when task-relevant material is not enough to fill our capacity, we automatically process other things in the environment.

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I find it helpful to imagine attention as a pint glass that we always have to fill. If we don’t fill it with task-relevant information, then the remainder will automatically be topped up by other stimuli from the environment.

Let’s think of an example. Imagine doing a spot-the-difference task with only three objects in the picture. You would likely find the different object very quickly, and also very easily. You would probably also find that you don’t lose yourself in the task; you are still aware of background noises or movement in your surroundings. This is because the low level of attentional load in the task is not exhausting our attentional capacity (it doesn’t fill the pint glass), so we process other things as well.

Now, imagine a more difficult spot-the-difference task, with one change hidden in a complex picture of 30 or so objects. You will likely find this task much harder, but you would also probably be much less aware of other things happening in your surroundings as you completed it. This task would fill the pint glass of attention, owing to its increased perceptual load, leaving you less likely to process anything else.

Imagine attention as a pint glass that we always have to fill

That’s what perceptual load theory is. But what are the implications for classroom practice? 

1. Teachers might like to experiment with ways of increasing the attentional load of presentations. By delivering complementary information across multiple sensory modalities, you can aim to fill the pint glasses of students’ attention. Dual coding, when done successfully, might be an example of this.
    
2. Aim to set appropriately challenging tasks, as these are more likely to fill attentional capacity.
    
3. Reduce the number of obvious potential non-task-related distractors in classrooms. For example, eye-catching displays should not be around the board or at the front of the room, where you want attention to be focused.
    

Working memory load

Once we have allocated attention to a particular piece of information, it is able to proceed further down the processing stream.

Now we enter a second limited-capacity environment - working memory - and so find ourselves operating under a new load theory: working memory, or cognitive load.

Confusingly, the psychology and cognitive neuroscience research treats these terms as pretty much interchangeable, and neither of them refers to the “cognitive load theory” (CLT) that teachers might be most familiar with - the one that deals with the educational implications of limited capacity. We’ll return to CLT shortly, but for now we’ll stay on just analysing “working memory load”.

The capacity of working memory has been estimated at around four “chunks” of information. A chunk might be something as small as a single letter (if we have no meaningful connections to the information or no prior experience with such tasks) but it can contain considerably more information in other circumstances, depending on our expertise. For example, a whole chess board arrangement could occupy only a single chunk in very experienced chess players.

Working memory is also crucial for keeping track of our current goals and prioritising the processing of task-relevant chunks. This means that overloading working memory with too much information or too complex a task can make people more susceptible to distraction and poor task performance.

You may notice that, interestingly, this is the opposite of the effect of exhausting our perceptual capacity. When perceptual load is high, we become more resistant to distraction, as we do not process competing task-irrelevant information. 

Overloading working memory with too much information can make people more susceptible to distraction

Conversely, when working memory load is high - making it hard to track and prioritise which of the items we should be processing - distraction will be increased. This is assuming that initial perceptual load is low and so some attentional processing will have spilled over on to task-irrelevant items.

Some of the implications of working load theory in the classroom might be:

1. Teachers should reduce the number of steps in instructions that are given at any one time, or break down tasks into manageable chunks.
    
2. It is helpful to provide students with instructions for a task in written form, or in some other format that can be referred back to.
    
3. Teachers should manage the complexity of tasks to avoid them becoming overloading - although this does not mean making things as easy as possible, given that appropriate challenge will occupy perceptual capacity more effectively. 

Both perceptual and working memory capacity appear to develop throughout childhood. Perceptual capacity reaches adult levels by age 12 or so; earlier than this, a smaller amount of information is required to fully load children’s capacity. 

Working memory, meanwhile, seems to develop slightly later, into the mid-teens. 

Cognitive load theory

But what about CLT, that staple of evidence-based teaching and learning presentations for the past few years? Cognitive load theory builds on the implications of both of the load theories above to produce a more education-specific theory of “instructional design”. In other words, it considers how we should design learning and educational experiences, given the existence of limited capacity bottlenecks in our processing system.

It is sometimes suggested that CLT is a theory based on working-memory limitations but, in fact, a number of the “effects” noted by the theory are also the consequence of a limited attention capacity. The “split attention effect” (where performance is impaired by having to split attention between complementary information in two different sources or locations) is the most obvious of these, but another example is the “transient information effect” (where information is removed before the learner has had time to process it properly).

The latter is partially a product of our limited perceptual load capacity and the fact that we always fill our perceptual capacity fully. This means that as soon as the target information is removed, other task-irrelevant information will stream in and compete for processing in a limited working memory. 

If we process redundant material, there is not enough space to attend to all the necessary information

The so-called “redundancy effect” (where information that is not needed, or is needlessly repeated, leads to less successful learning) is also likely to be partially due to our limited attentional capacity. If we process some of the redundant material, there is not enough space to attend to all the necessary information.

In contrast, the “modality effect” (where complementary material presented through both auditory and visual channels leads to better learning) takes advantage of the fact that the capacity of both attention and working memory seems to be slightly larger when split across different sensory modalities.

We, therefore, have a system of two separate, and sometimes seemingly slightly paradoxical, theories of limited capacity, with a further educational theory built on top.

It’s a complicated picture, and that’s without factoring in other overlapping educational theories, such as Richard Mayer’s “cognitive theory of multimedia learning”.

It is perhaps understandable that there might be some confusion at times, then. 

Still, the next time a CPD session starts to overload you with ideas about limited capacity, it might be worth checking whether the speaker knows exactly which load they are talking about.

Michael Hobbiss is a psychology teacher and cognitive neuroscience researcher