If a target exceeds the summation area, the number of quanta required for threshold detection will:

If a target exceeds the summation area, the number of quanta required for threshold detection will:

• A. Decrease
• B. Stay the same
• C. Increase
• D. Vary

Answer: (C)

The key idea is how spatial summation determines threshold detection. The detector only sums light over a fixed summation area, so only photons falling inside that area contribute to the signal. If the target is larger than this area, photons outside don’t help reach the threshold. To trigger the same detectable response, more total quanta must be delivered so that enough photons still land within the summation area. In short, exceeding the summation area means you need more quanta to reach threshold.

The key idea is how spatial summation determines threshold detection. The detector only sums light over a fixed summation area, so only photons falling inside that area contribute to the signal. If the target is larger than this area, photons outside don’t help reach the threshold. To trigger the same detectable response, more total quanta must be delivered so that enough photons still land within the summation area. In short, exceeding the summation area means you need more quanta to reach threshold.