Mental load: how to avoid overheating your brain?
Is it possible to read emails while thinking about weekend plans and listening to someone on the phone? Welcome to so-called multitasking, which has become part of our daily lives with remote working and the rise of digital technology. We may feel like we're doing two things at once, but in reality, our brains unconsciously shift their attention very quickly from one task to another. After more than 50 years of scientific research, the term "mental load" has become more common in everyday life and in various professional circles in recent years. But this concept still raises many questions, both about its precise definition and how to study it or manage it on a daily basis.
Stéphane Perrey, University of Montpellier
Mental load, also known as mental workload, refers to the amount of mental work that must be performed in a given time, which can have consequences for the individual, such as accumulated fatigue or errors in task performance. Take, for example, the intensive practice of a manual skill, a difficult exam, driving on a busy highway, or searching through a cluttered visual display. These activities involve perceptual, cognitive, and/or motor processes in order to produce flexible and adaptive behavior. Engaging, maintaining, and controlling these processes requires varying levels of mental effort depending on the circumstances (routine activities versus sudden events). Sometimes, this massive mental effort leads to what scientists call "cognitive overload" or "mental overload."
A universal definition that is struggling to emerge
Researchers are still struggling to come up with a universal definition that spans the disciplines concerned with mental load, such as psychology, management, and cognitive science. For some, mental load corresponds to the notion of an individual's limited capacity (a "reservoir" of attentional resources) to process information. For others, it refers to the management of attentional resources and focuses on the demands of the task at hand. Among the many definitions proposed in the literature, it appears that mental load can be defined as the amount of effort invested by an individual in performing a task based on their available resources and the characteristics of the task.
In neuroscience, cognitive psychology, and ergonomics (the scientific discipline that studies the relationship between humans and their work), the study of mental load focuses in particular on applications that are considered "safety-critical." These include fields such as automotive, aviation, air traffic control, space flight, and defense. In situations where the cognitive cost exceeds the available resources, the resulting overload increases the risk of accidents, due to the individual's difficulty in detecting technical anomalies or warning signals. This is referred to as attentional deafness. This can be the case, for example, for an airplane pilot during landing or in poor weather conditions. More recently, studies on mental load have also attracted research interest in the fields of media, human-machine interaction, medical training, sports, and finance.
While laboratory studies have advanced our understanding of brain functions during a given task, it is important to evaluate individual performance and mental load in the complex work environments encountered in everyday life. This is one of the leitmotifs of neuroergonomics, a discipline dating back to the late20thcentury, which aims to synthesize the approaches and tools used by neuroscience with the field-based approach of ergonomics and engineering. Based on a multidisciplinary approach, neuroergonomics is defined asthe study of the human brain in relation to performance at work and in everyday life. One example is the measurement of brain activity in surgeons, for whomincreased mental load can lead to errors and negatively affect performance.
How can mental load be studied? From behavioral responses to neurophysiological markers
Just as there are many possible definitions of mental load, there are many ways to measure it. No single tool or method can provide a complete picture of how an individual responds to a task. Approaches that combine data from multiple sensors or measurements are therefore necessary and can be more accurate and reliable for estimating mental load in real time. This is especially true in changing environments (fluctuations in lighting, temperature, etc.) or contexts that require adaptation to the situation (discomfort, technical incidents, etc.).
Self-assessment questionnaires on perceived mental workload enable the collection of individuals' perceptions while performing the task. For example, by incorporating a multidimensional assessment procedure, the NASA-TLX questionnaire provides an overall score of mental workload during or after the task. It is based on a weighted average of scores (from 0 to 100) from six subjective subscales. These scales are mental demand (level of mental activity), physical demand (level of physical activity), time pressure (feeling of pressure to complete the task within a given time frame), performance (level of task goal achievement), effort (amount of effort expended), and frustration (feeling of dissatisfaction during task completion).
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Analyzing performance when performing a single task can also help estimate mental load. For example, more frequent errors or a decrease in information processing speed may indicate a higher mental load if the demands of the task increase. In the case of a dual cognitive-motor task (talking on the phone while driving, navigating while cycling or walking, etc.), the sharing of resources thus created can lead to a drop in performance compared to performing each of the two tasks separately.
In addition, neuroergonomics proposes integrating objective measures to assess mental workload using several ambulatory techniques in environments that vary over time (workplaces, classrooms, operating rooms, traffic, etc.). For example, eye-tracking analysis can provide information on mental workload by measuring where an individual directs their attention. Physiological measurements, such as heart rate and its variability, electrodermal activity, and even portable brain imaging, can provide specific neurophysiological indicators of mental workload.
In the brain, the prefrontal cortex is a privileged witness to mental load.
Mental load manifests itself particularly in the prefrontal cortex, the area of the brain that has undergone the most significant development in humans over the last few million years. This part of our brain is heavily involved in cognitive control, a mechanism for adapting and supervising the decision-making process. Cognitive control is involved in conflict resolution, error detection, and inhibition, and aims to ensure a sufficient level of performance in relation to task requirements and unexpected events, while maintaining an acceptable cognitive cost. Measuring the activation of the prefrontal cortex by observing how much energy it consumes, i.e., glucose and oxygen, can provide information about the amount of resources mobilized to meet the demands of the task. Indeed, difficult tasks or those requiring sustained attention lead to more pronounced activation of the prefrontal cortex and associated brain networks.
This is also the case during demanding physical exertion in complex environments, such as cycling in heavy traffic, where each individual can decide to engage differently in the exercise after assessing the costs and benefits. In this situation of dual physical and cognitive tasks, the decision on speed is cognitively controlled, probably guided by a strategic decision aimed at maximizing benefits in relation to costs.
Managing mental load
In demanding professional or educational contexts, or in other situations such as driving, mental load can vary over time until it becomes overwhelming under the influence of various external and internal factors. How can we cope with the multitude of factors we need to pay attention to?
Several recommendations can be applied on an individual level. On the one hand, it is often useful to draw up an overview of all the tasks to be performed in order to prioritize them. This allows you to build a sequence of tasks to be completed one after the other, and to abandon non-essential tasks in order to better value the work done. Each task should correspond to specific short-term objectives (around 20 minutes). It is also important to adapt breaks to the task at hand in order to effectively regulate mental load and reduce distracting interruptions. Finally, it is important to always allow yourself adequate recovery time (reading, sports, etc.).
Applying the principles of neuroergonomics can provide personalized and effective solutions for managing mental load. Research on mental load remains extremely relevant, particularly in terms of taking into account individual variability in how people process information and interact with their environment. As such, the use of artificial intelligence methods to extract congruent information from several combined measurements represents an interesting avenue for continuously assessing the mental load of an individual engaged in a task.
Stéphane Perrey, University Professor of Exercise Physiology/Integrative Neuroscience, Director of the Research Digital Health in Motion Research Unit, University of Montpellier
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