Two-point discrimination is influenced by the degree of convergence of primary sensory inputs. Which factor best explains variability in discrimination?

• A. Its conduction velocity
• B. Degree of convergence of primary sensory inputs
• C. Temperature of skin
• D. Skin thickness

Answer: (B)

Two-point discrimination hinges on how finely the nervous system can keep separate touch signals from neighboring skin areas. The crucial factor is how many primary sensory inputs converge onto a single central neuron. If many inputs converge, signals from two close points get pooled together, so the brain cannot distinguish them as separate—discrimination worsens. If there is little convergence, the inputs stay distinct, allowing finer spatial resolution. This explains why fingertips, with small, densely packed receptive fields and relatively low convergence, have excellent two-point discrimination, while larger skin areas with more convergence show poorer discrimination. Other factors like conduction velocity, skin temperature, or skin thickness influence other aspects of sensation but do not account for the variability in spatial discrimination as directly as the degree of convergence.