Sensation: Thresholds, Signal Detection, and Vigilance
📘 5.1 Sensation: Thresholds, Signal Detection, and Vigilance
(संवेदन: थ्रेशोल्ड, सिग्नल-डिटेक्शन और सतर्कता)
🔍 What is Sensation?
Sensation is the process by which sensory receptors and the nervous system receive and represent stimulus energies from the environment. It is the raw data before interpretation (which is perception).
🧪 I. Thresholds in Sensation
📌 a) Absolute Threshold
- The minimum intensity of a stimulus that can be detected 50% of the time.
- Varies by sense (e.g., vision, hearing, taste).
🔹 Example:
- A candle flame seen from 30 miles away on a dark, clear night.
- The lowest volume at which you hear your phone ring.
👀 In UPSC context: While taking long sittings, attention fatigue may raise your threshold to ambient noise (you stop noticing a fan’s hum).
📌 b) Difference Threshold (Just Noticeable Difference – JND)
- The minimum change in a stimulus required to detect a difference.
🔹 Example:
- If you can detect a 1g increase in a 100g weight, the JND is 1%.
- In retail: A slight price increase that customers don’t notice falls below JND.
📘 Related Law:
Weber’s Law: The JND is a constant proportion of the original stimulus.
🧩 Practical Insight:
Brand designers make small changes in logos or taste to stay below JND and maintain familiarity.
🎯 II. Signal Detection Theory (SDT)
📌 Concept:
SDT explains how we detect a stimulus under uncertain conditions, factoring in both:
- Stimulus strength (signal)
- Psychological state (fatigue, expectation, motivation)
| Outcome | Signal Present | Signal Absent |
|---|---|---|
| Detected | Hit | False Alarm |
| Not Detected | Miss | Correct Rejection |
🔹 Example:
- A soldier at a border hears a faint rustle:
- If it’s an enemy → Hit
- If it’s a bird and he shoots → False Alarm
📌 Implication for UPSC students:
Fatigue and stress reduce sensitivity — you may miss a key term in a question (miss) or over-interpret a neutral statement (false alarm).
👁️ III. Vigilance (Sustained Attention)
📌 Definition:
Vigilance is the ability to maintain attention and remain alert over prolonged periods to detect rare or infrequent events.
🔹 Example:
- An air traffic controller watching for anomalies.
- A student revising for UPSC and identifying important keywords in long NCERT texts.
🧠 Key Factors Affecting Vigilance:
- Task complexity
- Motivation
- Fatigue
- Boredom
📉 Vigilance Decrement:
Performance typically drops after 30–45 minutes, unless rest or variety is introduced.
🧠 Theories/Models
- Weber-Fechner Law: Relationship between actual stimulus and perceived intensity
- SDT Model: Mathematically predicts response tendencies under uncertainty
- Yerkes-Dodson Law: Moderate arousal leads to peak vigilance
🇮🇳 Indian Examples and Applications
- ISRO Launch Monitoring – Scientists monitor systems for hours. Alertness training and work shifts maintain vigilance.
- UPSC Prelims MCQ Reading – Success depends on detecting slight differences in options — a test of sensitivity and signal detection.
🎓 Mains Application
GS Paper IV – Ethics Case Study
- An officer missing a critical alert in a disaster-prone area due to fatigue: How vigilance protocols could help prevent ethical lapses.
Essay Topic:
- “Attention to detail distinguishes the exceptional from the average.”
✅ Summary
| Term | Meaning | Example |
|---|---|---|
| Absolute Threshold | Minimum stimulus detected 50% of time | Hearing test |
| JND | Smallest detectable change | Price sensitivity |
| Signal Detection | Decision under uncertainty | Military alert |
| Vigilance | Sustained alertness | Exam hall, radar ops |
✍️ Answer Writing Format
Intro: Define sensation
Body: Explain thresholds, SDT, vigilance with examples
Diagram: SDT response table
Conclusion: Link to behaviour, performance, and public service relevance
