Tsukuba, Japan—During deep sleep, brain wave amplitude increases, and "δ (delta) power," a key objective indicator of sleep quality, is observed; higher delta power corresponds to deeper, more ...

Lindsey Ellefson is Lifehacker’s Features Editor. She currently covers study and productivity hacks, as well as household and digital decluttering, and oversees the freelancers on the sex and ...

Multitasking usually lowers productivity because most people are “task switching,” which creates a mental “switch cost” that slows processing and reduces accuracy. Switching between tasks strains ...