Weber´s Law (Sensory Processing): Proportion & Examples – Sensing the Environment | Lecturio

Main Ideas

• Weber’s law describes how much a stimulus must change for a person to notice a difference. The change must reach a roughly constant proportion of the original stimulus, rather than a fixed amount.
• The difference threshold, also called the just noticeable difference (JND), is the smallest change a person can detect.
• The required proportion depends on the sensory modality. The lecture gives these approximate average JNDs:
  • Weight: 2%
  • Light: 8%
  • Sound: 3%

These are general estimates and can vary; each sense has its own Weber constant.

Weber’s Law Equation

[ \frac{\Delta I}{I}=k ]

• ΔI: The difference threshold, or JND
• I: The original stimulus intensity
• k: Weber’s constant—the proportion of change needed for detection in that sensory modality

Worked Example: Timmy and Grocery Bags

1. Timmy can distinguish a 25-pound bag from a 30-pound bag.
2. The change is 5 pounds relative to an initial weight of 25 pounds:

[ \frac{30-25}{25}=\frac{5}{25}=0.20 ]

1. This means Timmy’s estimated weight threshold is a 20% change.
2. Apply that threshold to the choices:
   • 2 lb vs. 3 lb: The change is (1/2=50\%). Because 50% exceeds 20%, Timmy should detect the difference.
   • 20 lb vs. 22 lb: The change is (2/20=10\%). Because 10% is below 20%, he should not detect the difference.

Subtitle correction: The transcript contains inconsistent arithmetic and later calls Timmy’s threshold 25%. Based on the stated 25-to-30-pound comparison, the correct calculation is (5/25=20\%), which also matches the lecture’s final comparison.

Speakers and Sources Featured

• Lecturer/narrator: The Lecturio instructor; the video metadata identifies the professor as Dr. Tarry Ahuja.
• Weber’s law: The principle being explained.
• Timmy: A hypothetical grocery clerk used in the example, not a separate speaker.