Final answer:
The two-point discrimination threshold is closer on the fingertips because of the higher density of tactile receptors and greater brain representation, leading to better ability to discern distinct stimuli as compared to the palm, arm, or shoulder.
Step-by-step explanation:
The concept being discussed is known as two-point discrimination, which is a measure of tactile acuity on the skin. This measure varies across different body parts. The distance between caliper points is closer on the fingertips compared to the palm of the hand because the fingertips have a higher density of tactile receptors and a larger representation in the sensory cortex of the brain. As a result, the fingertips have greater tactile acuity and can discern between two closer points as distinct stimuli. On the other hand, areas like the arm or the shoulder would have a larger two-point discrimination threshold because they have fewer tactile receptors and a smaller representation in the sensory cortex, leading to a reduced ability to discriminate between two closely spaced points.