the cost of context switching

This room is a joke about it: three screens, two lists of demands, a scroll, and a printer that will not stop. Every one of them wants you to switch. Here is what switching actually costs, and what helps.

what the research says

• Switching is never free. Decades of lab studies find a reliable "switch cost": right after changing tasks, people are slower and make more errors, and the penalty grows with task complexity (Monsell 2003 [1]; Rubinstein, Meyer and Evans 2001 [2]). David Meyer, one of the study's authors, has estimated that the brief mental blocks created by switching can eat up to 40 percent of someone's productive time (the estimate is his summary, via the American Psychological Association [3]).
• Real offices are fragmentation machines. Gloria Mark's field studies at UC Irvine shadowed information workers and clocked them at roughly three minutes on a task before switching, and about eleven and a half minutes in one "working sphere" before being pulled to another (Mark, Gonzalez and Harris 2005 [4]).
• About that famous "23 minutes to refocus": the number comes from an interview with Mark about her field work, not from a published paper. Her published experiment found something subtler: interrupted people actually finished the work faster, but paid in significantly more stress, frustration and time pressure (Mark, Gudith and Klocke 2008 [5]).
• Part of your mind stays behind. Sophie Leroy showed that when you switch away from an unfinished task, "attention residue" lingers and measurably hurts performance on the next task (Leroy 2009 [6]).
• Heavy multitaskers do not adapt. People who chronically juggle many media streams test worse at filtering out irrelevant information, and worse at switching itself (Ophir, Nass and Wagner 2009 [7]).
• Per project, it compounds. Gerald Weinberg's classic rule of thumb: each additional simultaneous project costs roughly 20 percent of your time in switching overhead. An estimate from consulting experience, not a controlled study, but it has aged well (Weinberg 1992 [8]).

what helps

• Leave a "ready to resume" note. Spending under a minute writing down where you stopped and what comes next sharply reduces attention residue on the following task (Leroy and Glomb 2018 [9]). The Kanban board on the wall over there is one way to park a task properly.
• Batch the interrupters. People assigned to check email only a few set times a day felt less stressed than people checking freely (Kushlev and Dunn 2015 [10]). Phone notifications delivered in three daily batches improved attention, mood and sense of control versus arriving one by one (Fitz and colleagues 2019 [11]).
• Switch at natural breakpoints. The same interruption costs far less at a task boundary (just finished a unit of work) than mid-thought (Adamczyk and Bailey 2004 [12]). If you must switch, finish the sentence first.
• Give each kind of work its own place. Memory is context dependent: divers who learned word lists underwater recalled them best underwater, and on land best on land (Godden and Baddeley 1975 [13]). A distinct environment per kind of work (a desk for making, a corner for reading, a room for calls) gives each task its own retrieval cues, so re-entry costs less. Honest footnote: that is an extrapolation from memory research; nobody has run the diving study on your office. It is also, obviously, the whole idea of this website.
• Take real breaks. A walk in nature restored the kind of directed attention that switching burns, significantly better than the same length walk through city streets (Berman, Jonides and Kaplan 2008 [14]).
• Mostly: do less at once. The bear's demands, the robot's demands and jay's scroll all want to be your working sphere. Fewer parallel projects means fewer switches to pay for ([2], [8]). Breathe, pick one thing, and let the rest wait on the corkboard.

citations

1. Monsell, S. (2003). Task switching. Trends in Cognitive Sciences, 7(3), 134-140. doi.org/10.1016/S1364-6613(03)00028-7
2. Rubinstein, J. S., Meyer, D. E., and Evans, J. E. (2001). Executive control of cognitive processes in task switching. Journal of Experimental Psychology: Human Perception and Performance, 27(4), 763-797. doi.org/10.1037/0096-1523.27.4.763
3. American Psychological Association (2006). Multitasking: switching costs. apa.org/topics/research/multitasking
4. Mark, G., Gonzalez, V. M., and Harris, J. (2005). No task left behind? Examining the nature of fragmented work. CHI 2005. doi.org/10.1145/1054972.1055017
5. Mark, G., Gudith, D., and Klocke, U. (2008). The cost of interrupted work: more speed and stress. CHI 2008. doi.org/10.1145/1357054.1357072
6. Leroy, S. (2009). Why is it so hard to do my work? The challenge of attention residue when switching between work tasks. Organizational Behavior and Human Decision Processes, 109(2), 168-181. doi.org/10.1016/j.obhdp.2009.04.002
7. Ophir, E., Nass, C., and Wagner, A. D. (2009). Cognitive control in media multitaskers. Proceedings of the National Academy of Sciences, 106(37), 15583-15587. doi.org/10.1073/pnas.0903620106
8. Weinberg, G. M. (1992). Quality Software Management, Volume 1: Systems Thinking. Dorset House.
9. Leroy, S., and Glomb, T. M. (2018). Tasks interrupted: how anticipating time pressure on resumption of an interrupted task causes attention residue, and how a "ready-to-resume" plan mitigates the effects. Organization Science, 29(3), 380-397. doi.org/10.1287/orsc.2017.1184
10. Kushlev, K., and Dunn, E. W. (2015). Checking email less frequently reduces stress. Computers in Human Behavior, 43, 220-228. doi.org/10.1016/j.chb.2014.11.005
11. Fitz, N., Kushlev, K., Jagannathan, R., Lewis, T., Paliwal, D., and Ariely, D. (2019). Batching smartphone notifications can improve well-being. Computers in Human Behavior, 101, 84-94. doi.org/10.1016/j.chb.2019.07.016
12. Adamczyk, P. D., and Bailey, B. P. (2004). If not now, when? The effects of interruption at different moments within task execution. CHI 2004. doi.org/10.1145/985692.985727
13. Godden, D. R., and Baddeley, A. D. (1975). Context-dependent memory in two natural environments: on land and underwater. British Journal of Psychology, 66(3), 325-331. doi.org/10.1111/j.2044-8295.1975.tb01468.x
14. Berman, M. G., Jonides, J., and Kaplan, S. (2008). The cognitive benefits of interacting with nature. Psychological Science, 19(12), 1207-1212. doi.org/10.1111/j.1467-9280.2008.02225.x