Why is multitasking actually lowering your IQ by 10 points?

Question

Accepted Answer

The claim that multitasking lowers IQ by 10 points originates from research conducted by Dr. Glenn Wilson at the University of London. This study suggested that the cognitive impairment caused by constant interruptions—such as checking emails or responding to instant messages while performing a primary task—is statistically equivalent to losing 10 IQ points.

Here is why this phenomenon occurs:

Cognitive Switching Costs: The human brain is not wired to perform multiple complex tasks simultaneously. Instead, it performs "task switching." Every time you shift your attention from one task to another, your brain must undergo a process of "context switching," which consumes significant neurological resources and time.
   The "Attention Residue" Effect: Coined by organizational psychologist Sophie Leroy, this concept explains that when you switch from Task A to Task B, your attention does not immediately follow. A portion of your cognitive resources remains stuck on the previous task. This "residue" reduces your working memory capacity and prevents you from reaching a state of "deep work" or "flow."
   Prefrontal Cortex Overload: The prefrontal cortex is responsible for executive functions, including planning, decision-making, and focus. Constant multitasking overstimulates this area, leading to decision fatigue and an increase in error rates. Because the brain is forced to process competing streams of information, it prioritizes rapid, superficial processing over deep, analytical thought.
   Dopamine Feedback Loops: Multitasking often involves digital interruptions that provide "micro-rewards" (such as a notification ping). These trigger dopamine releases, which create a cycle of distraction. This keeps the brain in a state of high-arousal, low-focus activity, which is antithetical to the sustained concentration required for high-IQ performance.
   Working Memory Depletion: IQ tests heavily measure working memory—the ability to hold and manipulate information. Multitasking clutters this limited mental workspace with extraneous data, effectively lowering your functional intelligence in the moment, even if your underlying cognitive ability remains unchanged.

In summary, multitasking does not permanently lower your IQ, but it temporarily compromises your cognitive efficiency. By forcing the brain to constantly restart its focus, you operate at a fraction of your actual intellectual capacity, resulting in the observed 10-point deficit in performance.