Mental Reserve

Solution: Mental Reserve

Mental Reserve describes a real-time, session-level metric derived from cumulative cognitive load and is grounded in the mental fatigue literature, which defines mental fatigue as a decrease in mental performance resulting from cognitive overload — due to task duration and/or workload — independent of sleepiness.

Mental Reserve reflects how much cognitive capacity a person has left in reserve, as shaped by their cognitive load over time. People rarely operate at a single, steady level of mental effort — cognitive load naturally fluctuates, and periods of sustained high cognitive load gradually deplete available resources (Borragán et al., 2017; Hu & Lodewijks, 2020). When mental reserve runs low, the effects are tangible: attention narrows, decision-making slows, and errors become more likely. Monitoring how much of a session is spent at high cognitive load is therefore a key indicator of sustained performance, resilience under pressure, and the likelihood of cognitive overload (Boksem & Tops, 2008; Chen et al., 2018).

HarmonEyes uses the eye tracking signal, machine learning and AI to answer the following question related to mental reserve:

What percentage of your session have you spent in high versus low cognitive load?

Mental Reserve is calculated as a running percentage of time spent in each demand state, updated every second starting one minute into a session:

• Low Demand: Time spent in low or moderate cognitive load — mentally engaged but with capacity to spare.
• High Demand: Time spent in high cognitive load — operating near or at mental capacity. Research shows that prolonged high-demand work depletes working memory resources and leads to impaired attention, planning, and decision-making (Boksem & Tops, 2008; Chen et al., 2018).

For example, a session showing 70% Low / 30% High indicates that most of the session was spent with meaningful cognitive reserve intact.