·Psychology & Behavior
Section 1
The Core Idea
In 2009, Sophie Leroy at the University of Minnesota published a paper that should have restructured every calendar in every knowledge-work organisation on the planet. The finding: when you switch from Task A to Task B, part of your cognitive processing remains stuck on Task A. Leroy called this "attention residue." The residue is not a feeling. It is a measurable degradation in performance. Subjects who switched tasks while Task A was incomplete performed significantly worse on Task B than subjects who completed Task A before switching. The attention didn't transfer cleanly. It leaked.
The residue persists for 15 to 25 minutes. During that window, you are cognitively impaired — not dramatically, not in a way you'd notice subjectively, but in a way that shows up in error rates, decision quality, and creative output. You feel like you're working on Task B. You are actually running two cognitive processes: working on Task B while your mind continues processing the unresolved elements of Task A. The result is neither task gets your full capacity. You are half-present twice rather than fully present once.
Cal Newport built his entire
Deep Work thesis on this foundation. His argument: knowledge workers who fragment their attention across tasks, emails,
Slack messages, and meetings never reach the state of deep cognitive engagement where the highest-value intellectual work happens. They can't — the attention residue from each interruption degrades the next 15-25 minutes of cognitive function. By the time the residue clears, the next interruption arrives. The worker spends the entire day in a degraded cognitive state, producing shallow output at a fraction of their potential.
Gloria Mark at UC Irvine quantified the fragmentation. Her research found that the average knowledge worker switches tasks every 11 minutes. Not every hour. Not every 30 minutes. Every 11 minutes. And after each switch, Leroy's research predicts 15-25 minutes of residue. The math is devastating: if you switch every 11 minutes and the residue lasts 15 minutes, you never clear the residue from the previous switch before the next one arrives. You spend the entire workday in a state of continuous partial attention — never fully engaged with anything, always carrying cognitive debris from the last thing you touched.
Microsoft Research confirmed the recovery cost from a different angle. Their study found that after a single email interruption, workers took an average of 23 minutes to return to the original task — not to reach peak performance on the task, but simply to re-engage with it at all. Many workers never returned. They got pulled into a cascade of related tasks triggered by the interruption and ended the day having abandoned the original work entirely.
The strategic implication is stark. Time-blocking, maker schedules, meeting-free days, and notification discipline are not productivity hacks. They are not personal preferences or lifestyle choices. They are structural defences against a cognitive vulnerability that degrades every knowledge worker's output every day. An organisation that fragments its workers' attention with constant interruptions is not just annoying its employees. It is systematically preventing them from doing their best work.
