The Science of Doing Too Many Things At Once

Picture this: You are watching your favorite show on Netflix and you receive a text message. Anxious to see who messaged you, you decide to break your gaze from the show, read the message, type a response, and click “send.” It’s only after shifting your attention back to the show that you realize that you have no idea what happened in the last two minutes. Has this ever happened to you?

Dual-tasking, defined as performing two tasks at once, is something that many folks think they can do well. In fact, like me, you’ve probably heard several people claim that they can even multitask well. Perhaps you’re one of those people? Unfortunately, I have to burst your bubble and tell you that it is not possible to perform two or more tasks simultaneously (as in performing both tasks exactly at the same time). According to several research studies, no one can dual or multitask. What you’re actually doing when you think you’re dual or multitasking is something called task-switching, or unconsciously shifting your attention between tasks.

You may be asking yourself why this is important for you to know. Well, with the information that I’m about to give you, you will develop a solid understanding of which paired tasks you can perform better than others. This could translate to creating a safer environment for yourself and those around you, or even boosting productivity at work. Now that your interest is peaked, let’s go ahead and take a closer look at dual-tasking.

Why Walking and Chewing Gum at the Same Time is Harder Than you Think

Research has shown that dual-task performance is worse when compared to single-task performance. Worsening of performance from single to dual-tasks, referred to as performance cost or interference, happens for a number of reasons (Koch et al., 2018). Mostly, it’s all about architecture – brain architecture, that is – and the mental effort required to perform a task or attend to a stimulus. In the 80s, a researcher by the name of Wickens proposed something called the Multiple Resource Model (MRM). The general assumption of the MRM is that while performance deficits occur when tasks are time-shared, the cost is less severe when the two tasks do not share common perceptual or cognitive resources. The model, as you see below, is characterized with respect to the task type (i.e., modality), the way the information is processed (i.e., spatial/verbal), the demands on information processing, and the type of response required for task completion (i.e., manual, vocal). Factors such as operator skill level and a task’s utilization of working memory can influence task performance, as both tasks increase the demands on the task performer (Wickes, 1988). So that it makes more sense, let’s consider an example.

Photo sourced from https://www.researchgate.net/figure/The-4-D-multiple-resource-model-by-Wickens_fig2_260704057

Let’s say you’re driving your car along the highway – a task that requires visuospatial skills, spatial processing/coding, and manual responding – and you receive a text message. While driving, you read the text message – a task that requires visual perception, verbal processing/coding, and manual responding. The two tasks, as you see, overlap with respect to the type of perception (visual) and the response required (manual). That overlap is why it’s so difficult to perform both tasks at the same time and why you’re advised not to do it! Now, on the other hand, if you were to receive and answer a phone call –  a task that requires auditory processing and vocal responding – as opposed to a text, there would be little overlap, meaning that you would dual-task those tasks better than you would texting and driving.

So…can you guess why you can’t walk and chew gum concurrently as well as you could separately? While you probably recognized that there isn’t much overlap on the MRM – if you identified the overlap at the response stage, you were spot on – it would still be difficult to perform the tasks at exactly the same time as opposed to by themselves. Remember, whether the tasks are simple or not, your still task-switching.  

 Reminders and Advice

If you have to dual-task, remember to choose tasks that are dissimilar. If the tasks are similar in form and function, you won’t perform them well concurrently!

– You will never be able to perform two tasks together as well as you could separately.

– To task-switch better, lessen the load on your brain. In other words, choose tasks that are simpler and less demanding.

– Don’t text and drive.

Reference Words and Examples:

Spatial: “Spatial” relates to the placement of objects in space.

Visuospatial Skills: The ability to visually perceive the relationship between objects in space. When you are navigating using a paper map or rotating objects in your mind (think Tetris), you’re using visuospatial skills!

Working Memory: A part of short-term memory that holds information temporarily. When someone tells you their phone number and you’re forced to hold it in memory because you don’t have a pen, you’re using working memory!


Koch, I., Poljack, E., Müller, H., & Kiesel, A. (2018). Cognitive structure, flexibility, and plasticity in human multitasking – an integrative review of dual-task and task-switching research. Psychological Bulletin, 144(6), 557-583. https://doi-org.proxy-bc.researchport.umd.edu/10.1037/bul0000144

Wickens, C. D. (1988). Modes and modalities in multiple resources: A success and a qualification. Human Factors, 30(5), 599-616.  https://doi.org/10.1177/001872088803000505

If you would like to learn more about dual-tasking or how you can improve single-task performance, please check out Dr. Fotuhi’s Brain Fitness Program at NeuroGrow.com

Written by Brianna Sirkis and edited by Dr. Majid Fotuhi

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