A study conducted in the UK found that fNIRS can differentiate mental workload levels in reading tasks of varying difficulty
A study in the UK, led by researcher Serena Midha from the University of Nottingham and published in the International Journal of Human-Computer Studies, found that Functional Near-Infrared Spectroscopy (fNIRS) of prefrontal cortex activity can effectively differentiate workload levels in reading tasks, though not in writing tasks. fNIRS is a non-invasive neuroimaging technique that detects changes in blood flow and brain oxygenation, providing insights into cognitive and emotional processes. In the study, the technique was also able to detect changes in workload levels due to interruptions.
The term mental workload refers to the amount of cognitive effort and resources required to perform a specific task or set of activities. It’s a concept used to describe the demands placed on an individual’s cognitive system, including attention, memory, and decision-making processes. Mental workload can vary depending on the task complexity, individual expertise, and environmental conditions. When it hits a high level, it can lead to a decrease in performance, an increase in0 errors, and mental fatigue, while low mental workload may result in the underutilization of cognitive resources – and, ultimately, boredom.
Assessing mental workload is crucial in areas such as human factors, ergonomics, and cognitive psychology to enhance tasks, promote safety, and maximize overall performance. However, unlike physical workload, measuring mental workload is a complex challenge. So far, various methods have been employed for this assessment, including subjective reporting, physiological measuring, and performance-based metrics. However, they all have limitations.
One significant obstacle is the difficulty of measuring mental workload in real-world environments. That requires robust equipment, usually only available in specialized labs. Additionally, its use may interfere with performance or limit certain activities. Serena Midha and her team have explored the feasibility of employing fNIRS to monitor brain activity during tasks similar to office work, aiming to estimate mental workload.
fNIRS has two distinctive advantages over other techniques, such as Functional Magnetic Resonance Imaging (fMRI): how portable and lightweight it is. The system generally consists of a control unit for data acquisition and processing, as well as a set of optodes positioned on the scalp to monitor changes in light absorption. Optodes are components that integrate light sources, such as light-emitting diodes or lasers, and photodetectors to capture near-infrared light.
This groundbreaking study involved 20 participants – all healthy adults aged 31, including 8 women and 12 men. During the study, they underwent a series of reading and writing tasks, while their brain activities were monitored through fNIRS imaging.
The tasks were categorized into three groups according to the difficulty level: easy, moderate, and hard. In the easy reading task, participants read basic material related to their respective fields of study. In the moderate level, they read an academic paper they were unfamiliar with. Lastly, the hard task required them to continuously read the same paper, while performing another activity at the same time.
When it comes to writing, the easy task required the participants to send an email to the researcher describing their activities in the study so far. In the moderately difficult task, they detailed their study, suggested dates for a possible meeting, and explained their work. In the hard task, in addition to these requirements, participants had to continuously repeat the word “blah” while writing. Each task lasted 5 minutes.
During these activities, participants were interrupted three times by experimenters initiating generic conversations, which added an element of realism to the tasks. Additionally, they were allowed to consume coffee, tea, or water during the activities as a way to simulate typical work environments.
After each task, participants assessed their own mental workload by completing the NASA-TLX questionnaire, allowing for a deeper understanding of the cognitive challenges faced in different work contexts.
The results revealed that participants perceived difficult tasks as more challenging compared to those categorized as either easy or moderate. However, differences between the average ratings of easy and moderate difficulty tasks were not sufficient to prove that discrepancies were not just random variations. This pattern was consistent across all mental workload indicators evaluated in the questionnaire.
Analyses of fNIRS images showed that brain activity was lower during the moderate difficulty reading task, slightly higher in the easy task, and peaked in the hard reading task. Surprisingly, no significant differences in brain activity were observed between the three writing tasks. However, fNIRS was able to detect specific variations in brain activity during interruptions, especially regarding the tasks categorized as easy and hard.
The authors highlight that the positioning of optodes over the prefrontal cortex may influence the sensitivity of fNIRS to detect differences in mental workload between different types of tasks. Additionally, verbal interruptions during activities showed an impact on perceived mental workload, increasing when performed simultaneously with other tasks and decreasing when they temporarily became the main concern.
This study provides valuable insights into the dynamics of mental activity during reading and writing tasks in a simulated work environment. However, due to the small sample size and limited duration, results may vary in larger groups and with longer activities. The article “Measuring Variations in Mental Workload in Office Work Tasks using fNIRS” was written by Serena Midha, Horia A. Maior, Max L. Wilson, and Sarah Sharples.
