Final answer:
The two-point discrimination test estimates receptor density by measuring the minimum distance at which two points are perceived distinctly on the skin. The sensitivity and receptive field density are higher in the fingertips, resulting in a smaller two-point threshold compared to areas like the arm or shoulder.
Step-by-step explanation:
The two-point discrimination test is employed to estimate the receptor density of sensory receptors in human skin. It measures the ability to distinguish between two closely spaced stimuli touching the skin, thus determining the density of receptive fields and sensitivity to fine touch. This method involves using tools like calipers to apply two simultaneous touches to the skin, which can range from the fingertips to less sensitive areas like the shoulders. The minimum distance at which two points are perceived as distinct indicates the sensitivity of that area and, therefore, the density of pressure receptors. The fingertips, having a higher receptive field density, will have a smaller two-point threshold, signifying their heightened sensitivity, whereas areas like the arm or shoulder, with lower sensory receptor density, will have a larger two-point threshold.