Experiments in the 1980s with macaque monkeys, have isolated the structural resemblance between input vibrations the finger feels, measured in cycles per second, and representations of them in neural circuits, measured in action-potential spikes per second. This resemblance between two easily measured variables makes it unsurprising that they would be among the first such structural resemblances to be discovered. Macaques and humans have the same peripheral nervous system sensitivities and can make the same tactile discriminations. Subsequent research into neural processing has increasingly vindicated a structural resemblance or physical isomophism approach to how information enters the brain, is stored, and deployed.