Final answer:
Foveal local signs are less sensitive than foveal cones, which are densely packed for high-resolution vision and critical for seeing fine details. The sensitivity of the fovea can be demonstrated by focusing on a specific letter and noting the clarity of adjacent letters; the central vision is clear due to a high concentration of cones in the fovea.
Step-by-step explanation:
The foveal local signs are less sensitive to light when compared to the foveal cones themselves. This is because the fovea is densely packed with cones which are responsible for high-resolution vision. The cones in the fovea allow us to perceive fine details when looking directly at an object, which is essential for tasks like reading, where we focus on the letters directly in front of us. The size of the print in a word is much larger than the size of the rods and cones, hence when we focus on a particular letter like the 'G' in 'ROGERS', the details of the letter can be seen clearly due to the high density of cones in the fovea. The letters on either side of 'G' may appear less clear as they fall outside the direct line of foveal vision, which demonstrates the sensitivity of foveal vision.
By contrast, rods are spread throughout the rest of the retina and are more sensitive in low light conditions but do not contribute to the detailed vision provided by the fovea. Iris adjustment of the amount of light and the image processing by the eye-brain system also play a role in how clearly we can see things.