A surreal illustration depicting a tired brain navigating a confusing website.

Is Your Brain Sabotaging Your Website's Usability? The Truth About Cognitive Fatigue and User Experience

Kai Mendoza in Mind & Education August 2025 • 5 min read.

"Uncover how mental exhaustion impacts user testing and what it means for your site's design. Are your usability scores giving you a false sense of security?"

Cognitive fatigue—that feeling of mental exhaustion after prolonged periods of focused activity—is a well-known culprit in accidents and errors across various fields. From workplace mishaps to aviation incidents, a tired mind can significantly impair performance. But what about its impact on something less critical, yet still vital, like website usability?

We often assume users will interact with our websites when they're alert and focused. However, the reality is that people frequently browse the web after a long day at work, during their commute, or while juggling multiple tasks. This raises a critical question: does cognitive fatigue influence how users perceive and interact with a website, and, more importantly, does it skew traditional usability testing results?

This article delves into a study that investigates the effect of cognitive fatigue on subjective usability scores. By understanding how mental exhaustion affects user perception, we can gain valuable insights into creating more user-friendly and effective online experiences. Are your usability scores accurately reflecting the tired user's experience? Let's find out.

The Fatigue Factor: How Tired Minds Skew Usability Testing

A surreal illustration depicting a tired brain navigating a confusing website.

The central question addressed in the study is whether cognitive fatigue has a measurable impact on the subjective assessment of usability. In other words, do users who are mentally tired rate the usability of a website or system differently compared to when they are fresh and alert? Furthermore, if fatigue does play a role, does its effect differ based on the inherent usability of the system itself – is a poorly designed website affected more by user fatigue than a well-designed one?

To explore these questions, researchers conducted a study involving forty-three participants who were asked to evaluate the usability of prototype paper voting ballots. These ballots were intentionally designed with varying levels of usability – some were easy to use, while others were deliberately cumbersome. Participants completed a series of tasks both before and after undergoing a cognitive fatigue manipulation, and their subjective usability scores were recorded using the System Usability Scale (SUS).

The System Usability Scale (SUS): A widely used and validated tool for measuring subjective usability. It consists of a 10-item questionnaire that provides a single score representing the overall perceived usability of a system.
Cognitive Fatigue Manipulation: Participants engaged in a series of mentally demanding tasks designed to induce cognitive fatigue. These tasks included mental arithmetic, brain teasers, and attention-demanding exercises.
Prototype Paper Voting Ballots: Twelve prototype voting ballots which are classified as low usability or high usability. These ballots were randomly assigned and participants completed six ballots before a fatigue manipulation and six after the manipulation.

The study's results, surprisingly, did not reveal a significant main effect of fatigue on usability scores. In other words, there was no clear evidence that cognitive fatigue, on average, led to lower usability ratings. However, the researchers noted a high degree of variance in the usability of the systems assessed, suggesting that this variability may have masked the true effect of fatigue.

Beyond the Numbers: What This Means for UX Professionals

While the study didn't definitively prove that cognitive fatigue directly lowers usability scores, it highlights a critical consideration for user experience (UX) professionals: the mental state of users during testing. Traditional usability testing often aims for a controlled environment where participants are alert and focused. However, this may not accurately reflect real-world usage scenarios where users are often tired, distracted, or multitasking.

The high variance observed in the study underscores the importance of accounting for individual differences in user perception and cognitive state. Future research should explore methods for minimizing variability and maximizing the sensitivity of usability measures to detect the subtle effects of cognitive fatigue. Describing usability in a tiered system of low, medium and high might be advantageous, other than as binary.

Ultimately, understanding how cognitive fatigue influences user perception can lead to more robust and ecologically valid usability testing practices, resulting in websites and systems that are truly user-friendly, regardless of the user's mental state. Consider to manipulate the time of experimental manipulations in order to induce fatigue and become more time efficient.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1177/1541931213601850, Alternate LINK

Title: The Effect Of Cognitive Fatigue On Subjective Usability Scores

Subject: General Medicine

Journal: Proceedings of the Human Factors and Ergonomics Society Annual Meeting

Publisher: SAGE Publications

Authors: Ian Robertson, Philip Kortum

Published: 2017-09-01

Everything You Need To Know

What is Cognitive Fatigue, and why is it important in understanding website usability?

Cognitive fatigue is a state of mental exhaustion that can impact how individuals perceive and interact with a website. It's caused by prolonged periods of focused activity, such as a long day at work or multitasking. The article implies that understanding cognitive fatigue is crucial because it can skew the results of usability testing, making it difficult to create websites that are truly user-friendly. Cognitive fatigue can significantly impair performance and affect the assessment of website usability.

What is the System Usability Scale (SUS), and how was it used in the study?

The System Usability Scale (SUS) is a tool utilized in the study to assess the perceived usability of the prototype paper voting ballots. It is a widely used and validated 10-item questionnaire that provides a single score representing the overall perceived usability of a system. The study uses the SUS to measure participants' subjective usability scores of the ballots, before and after a cognitive fatigue manipulation, allowing researchers to examine the effect of mental exhaustion on usability assessment.

How did the study induce Cognitive Fatigue in its participants?

The study used a Cognitive Fatigue Manipulation to induce mental exhaustion in participants. This involved engaging them in mentally demanding tasks such as mental arithmetic, brain teasers, and attention-demanding exercises. The purpose of the manipulation was to simulate the cognitive fatigue users might experience in real-world scenarios, such as after a long day, and to observe how this fatigue affected their assessment of the usability of prototype paper voting ballots. By inducing this state, researchers could study how cognitive fatigue affects the subjective assessment of usability.

What role did the prototype paper voting ballots play in the study?

The study's primary focus was on prototype paper voting ballots, some of which were easy to use (high usability) while others were cumbersome (low usability). Participants evaluated these ballots before and after the cognitive fatigue manipulation. The use of ballots with varying usability levels allowed researchers to examine if cognitive fatigue impacts the usability of systems differently based on their inherent design. The ballots served as a controlled environment to test and measure the effect of cognitive fatigue on subjective usability scores.

What were the key findings of the study, and what do they mean for UX professionals?

The study revealed no definitive evidence that Cognitive Fatigue directly lowered usability scores. However, the variance in the systems assessed highlights a critical consideration for UX professionals: the mental state of users during testing. The study highlights that traditional usability testing often aims for a controlled environment where participants are alert and focused. This may not accurately reflect real-world usage where users are often tired, distracted, or multitasking. Therefore, UX professionals need to consider this when interpreting usability test results and designing websites to accommodate the needs of users in various mental states.