Sleep Deprivation: Cognitive Effects on Reaction Time, Memory, and Decision-Making
17–19 hours awake impairs psychomotor performance equivalent to 0.05% blood alcohol; after 24h without sleep, reaction time doubles; 2 weeks of 6h/night equals 48h total sleep deprivation.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| 17–19h awake impairment | 0.05 | % BAC equivalent | Psychomotor vigilance task performance; Williamson & Feyer 2000 |
| 24h awake impairment | 0.10 | % BAC equivalent | Above legal driving limit in all jurisdictions |
| Reaction time after 24h awake | 2× | increase | Mean reaction time on PVT doubles from ~250ms to ~500ms |
| 6h sleep for 14 nights | = 48h | total deprivation equivalent | Van Dongen et al. 2003; performance declines continuously; not plateaued |
| Working memory impairment | 1.5–2× | error increase | After one night without sleep; particularly working memory and attention |
| Decision-making risk tolerance | +30 | % riskier choices | Sleep-deprived individuals take significantly riskier decisions (Harrison & Horne 2000) |
The Alcohol Equivalence
One of the most striking findings in sleep deprivation research is the direct comparison to alcohol intoxication. Williamson and Feyer (2000) tested healthy subjects on psychomotor vigilance tasks both after extended wakefulness and after consuming known doses of alcohol:
| Wakefulness Duration | Performance Equivalent |
|---|---|
| 17–18 hours awake | 0.05% BAC (legal limit in Australia, most of Europe) |
| 19–21 hours awake | 0.08% BAC (US legal driving limit) |
| 24 hours awake | 0.10% BAC (intoxicated above all legal limits) |
Crucially, sleep-deprived individuals are significantly worse at recognizing their own impairment than alcohol-intoxicated subjects — increasing the risk of over-confidence in sleep-deprived decision-making.
Cumulative Sleep Debt
Van Dongen et al. (2003) conducted one of the most rigorous chronic sleep restriction studies: subjects restricted to 4, 6, or 8 hours per night for 14 consecutive days. Key findings:
- 8h/night: performance remained stable (sleep need met)
- 6h/night: continuous performance decline over 14 days; no plateau; day-14 deficits equivalent to 24h total deprivation
- 4h/night: performance degraded more rapidly; similar trajectory
Critically, subjects restricted to 6h/night felt only slightly sleepy by day 14, while their objective performance (psychomotor vigilance task) was severely impaired. This disconnect between subjective and objective impairment represents a serious safety risk — people believe they have adapted, but their performance has not.
Cognitive Domains Affected
Sleep deprivation does not impair all cognitive abilities equally. The most vulnerable are:
- Sustained attention / vigilance: the earliest and most severely affected; PVT reaction times lengthen within 24h
- Working memory: holding and manipulating information degrades rapidly
- Decision-making: prefrontal cortex activity decreases; individuals make riskier decisions and are less sensitive to negative feedback
- Emotional regulation: amygdala hyperreactivity; reduced prefrontal modulation; increased irritability and stress reactivity
- Creativity and divergent thinking: impaired ability to make novel associations
More “automatic” skills (procedural tasks, simple recall, well-practiced responses) are relatively preserved under acute sleep deprivation, which can mask impairment in complex cognitive tasks.
Microsleep
A critical danger of severe sleep deprivation is microsleep: involuntary sleep episodes lasting 0.5–15 seconds that occur without the person’s awareness. During a microsleep, the eyes may remain open and the person may not realize they lost consciousness. On the road or operating machinery, a 10-second microsleep at highway speed (70mph) means traveling 1,000 feet (300m) with no driver awareness.
Related Pages
Sources
- Williamson AM & Feyer AM — Moderate sleep deprivation produces impairments in performance equivalent to legally prescribed levels of alcohol intoxication. Occup Environ Med (2000)
- Van Dongen HPA et al. — The cumulative cost of additional wakefulness. Sleep (2003)
- Harrison Y & Horne JA — The impact of sleep deprivation on decision making: a review. J Exp Psychol Appl (2000)
- Dinges DF et al. — Cumulative sleepiness, mood disturbance, and psychomotor vigilance performance decrements during a week of sleep restricted to 4–5 hours per night. Sleep (1997)
Frequently Asked Questions
How does sleep deprivation affect driving?
Driving after 17–19h without sleep impairs performance equivalently to 0.05% blood alcohol concentration (BAC). After 24h, it equals 0.10% BAC — above the legal limit in all jurisdictions. The US National Highway Traffic Safety Administration estimates drowsy driving causes 100,000 police-reported crashes and 1,550 deaths annually. Critically, subjective sleepiness does not reliably predict objective impairment.
Can you recover from chronic sleep deprivation?
Complete recovery from chronic sleep deprivation takes longer than typically assumed. Subjective alertness normalizes after 2–3 recovery nights, but objective cognitive performance (reaction time, attention) requires 1+ weeks to fully recover, and some studies suggest certain neurocognitive deficits persist longer. The common belief that 'catching up on weekends' fully compensates weekday restriction is not supported by evidence.
Does sleep deprivation cause cognitive decline long-term?
Studies of lifelong shift workers and individuals with chronic sleep restriction show persistent cognitive impairments and increased dementia risk. The glymphatic clearance pathway — which removes amyloid-beta and tau during sleep — is impaired under chronic deprivation, potentially accelerating neurodegenerative pathology.