What stimulus size was used?

What stimulus size was used?

• A. 5 min arc
• B. 20 min arc
• C. 1 degree
• D. 10 min arc

Answer: (D)

The size of the stimulus is described in angular terms because it shows how large the image is on the retina. A stimulus of about 10 minutes of arc is small enough to activate a localized patch of photoreceptors, which helps reveal how a small retinal area responds without summing the signals from a large area. It’s also big enough to be reliably detected despite small eye movements or minor fixation drift, giving you measurable responses. If the stimulus were much smaller, like 5 minutes of arc, responses might be inconsistent or hard to detect. If it were larger, such as 20 minutes of arc or a full degree, many more photoreceptors would be involved, increasing spatial summation and making it harder to pinpoint responses to a specific retinal region.

The size of the stimulus is described in angular terms because it shows how large the image is on the retina. A stimulus of about 10 minutes of arc is small enough to activate a localized patch of photoreceptors, which helps reveal how a small retinal area responds without summing the signals from a large area. It’s also big enough to be reliably detected despite small eye movements or minor fixation drift, giving you measurable responses. If the stimulus were much smaller, like 5 minutes of arc, responses might be inconsistent or hard to detect. If it were larger, such as 20 minutes of arc or a full degree, many more photoreceptors would be involved, increasing spatial summation and making it harder to pinpoint responses to a specific retinal region.