Intertwining Cognitive Load & Perceptual Load

Cognitive Load Theory discusses intrinsic and extraneous load, while Load Theory of Attention discusses perceptual load – how similar and how different are these two theories?

At researchED Vancouver in February, I had the opportunity to discuss Nillie Lavie’s Load Theory of Attention and how it relates to Cognitive Load Theory and AD/HD. If you didn’t get a chance to attend, you can find a YouTube version of my talk here. This blog post is a summary of how I think Cognitive Load Theory and Load Theory of Attention appear to complement each other.

Sweller’s Cognitive Load Theory discusses the concepts of intrinsic and extraneous cognitive load through the use of the two major players in cognitive architecture: the working memory and the long-term memory store. Currently, it is theorized that the long-term memory store is infinite in capacity; yet the working memory, or processing space, has limited capacity. Not only can facts/information enter the working memory from the environment, but it also has some ability to “search out” stored facts/information from our long-term memory. When the capacity of the working memory is filled, and processing power becomes limited, we say an individual is experiencing cognitive overload.

Information can enter the working memory from either the environment or the long-term memory store. Here, the white circles represent the limited capacity of the working memory. Each black X represents information coming from the environment; whereas, each red X represents information from long-term storage. Ideally, we want learners to have some working memory capacity open for processing (blank white circle), so as not to experience cognitive overload.

One could imagine that if a lot of information, or cognitive demand, is coming from the environment, that this may quickly take up working memory space and lead to cognitive overload. With respect to teaching, the way we set-up, explain, and execute our lessons is referred to extraneous cognitive load. In other words, Cognitive Load Theory states that the way we present information and tasks to the learner is important. For instance, inquiry-based learning has a high extraneous load for novice learners compared to worked-out examples; yet worked-out examples tend to have a high extraneous load for expert learners compared to inquiry-based learning (an oddity known as the expertise-reversal effect).

If a task is cognitively demanding due to the way it is presented, such as inquiry-based learning for novices, extraneous cognitive load is high. If too much working memory capacity is taken up, we experience cognitive overload, and our ability to process new information decreases.

The same is true in the other direction. That is, one could imagine that if a question is intrinsically hard, then our working memory might try to “search out” a bunch of past knowledge from our long-term memory. With respect to teaching, Cognitive Load Theory states that we need to be mindful of how much mental effort is required of our learners to perform a particular task – this is known as intrinsic cognitive load. This type of cognitive load is often measured using element interactivity. For example, solving a related rates problem in calculus has high intrinsic load, as learners are required to keep track of many interacting elements (the picture or model, variable representing changing quantities, implicit derivatives, the original word problem); yet finding the derivative of y = x^2 is likely to have low intrinsic load.

If a task is cognitively demanding due to the task having many interacting concepts, intrinsic cognitive load is high. If too much working memory capacity is taken up, we experience cognitive overload, and our ability to process new information decreases.

Keeping Sweller’s Cognitive Load Theory in mind, let’s turn our focus to Lavie’s Load Theory of Attention. We will keep the two major players from before (working memory and long-term memory), and add in one new player: the sensory memory. It is believed that the sensory memory holds stimuli coming from the environment just long enough to be transferred to our working memory. Lavie’s Load Theory of Attention (or Perceptual Load Theory) discusses attentional capacities through the use of task-relevant stimuli and distractors. She theorizes that our attentional resources are of finite capacity, and that the perceptual load of task-relevant stimuli determines whether or not distractors get processed.

Before entering the working memory, stimuli have to pass through our sensory memory. It is here, where our brain selects which stimuli to pay attention to. Our attentional resources are of limited capacity,
similar to the working memory, and are shown with white circles.

One could imagine that, for a given task, there will be task-relevant and task-irrelevant information (or stimuli). Let’s call task-irrelevant stimuli distractors; these are the items we would like to keep away from our processing space. Suppose that the task-relevant stimuli don’t demand all of our attentional capacity in the sensory memory. In these cases, under low perceptual load, the leftover capacity is taken up by any number of distractors, and both the task-relevant stimuli and distractors are sent to the working memory space. Now distractors begin competing for processing space. For instance, consider a lecturer using PowerPoint. Assuming that you know the material very well, and it is easy to read the slides, you are in a scenario of low perceptual load. The free attentional capacity allows distractors to get through to your working memory space. You might begin to think about what is for dinner, the last song that played on the radio, why the person in front of you is wearing socks and sandals, or what new notification you received on your cell phone.

Task-relevant stimuli are indicated with a black X; whereas distractors are represented with a black D. Under the case of low perceptual load, task-relevant stimuli do not take up all of our attentional capacity, so distractors fill up the remaining space. Both distractors and task-relevant stimuli now have the ability to enter working memory and compete for processing space.

In contrast to the above scenario, imagine that the task-relevant stimuli do demand all of our attentional capacity in the sensory memory. In this case, under high perceptual load, the deficit in available attentional capacity results in distractors not taking up any of this space. Now only task-relevant stimuli are sent to the working memory for processing. For instance, consider the case where we are listening to a lecturer again. This time, we don’t know the material as well, and she is writing at the board in a handwriting style that is slightly messy. In this case of high perceptual load, our attentional capacity is maxed out trying to decode the handwriting and language used to explain the concepts. It is more challenging to think about distractors, as they aren’t vying for processing space in your working memory.

Under the case of high perceptual load, task-relevant stimuli take up all of our attentional capacity. Only task-relevant stimuli have the ability to enter working memory. Distractors are not processed.

As you might be able to see, the two theories developed by Sweller and Lavie seem highly complementary. Of interest to me is that it does not seem as though either theory has acknowledged the other as of yet. However, it does seem as though Perceptual Load Theory and Cognitive Load Theory might offer insights into each other’s realm:

  • How much of the extraneous load of a task comes from processing distractors?
  • Do distractors affect intrinsic cognitive load?
  • If we decrease extraneous cognitive load, does this always lead to less processing of distractors?
  • How can we create lessons in such a way to ensure that perceptual load is “high enough”? And how high is “high enough”?

I’m sure there are other concepts that could be intertwined as well, but these are some of the first questions that come to my mind. As always, I welcome your thoughts and questions on this reflection.



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