What Is a Stimulus Threshold?


Quick Answer

The stimulus threshold is the minimum change in a sensory stimulus that can be detected at least half of the time. Sensory receptor cells detect stimuli and changes of stimuli from the outside world and translate them into electrical signals that the brain can interpret.

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Full Answer

A subdefinition of stimulus threshold is the absolute threshold, which is the minimum amount of a stimulus that can be detected 50 percent of the time. Normally, the interior of neurons contain a slight charge of about -70 millivolts compared to the outside. Stimulation of the neuron activates sodium channels, which sends sodium into the neuron and increases its potential. Then ions are repelled from one neuron to the next, carrying the electrical signal across series of synapses to the brain and motor neurons that respond to the stimulus. Each neuron has an action potential, or the minimum voltage for it to activate. Action potentials operate on the all-or-nothing principle, as they do not activate unless their action potential is reached.

The stimulus threshold for various senses can sound impressive. For example, humans have demonstrated the ability to see the light of a candle from up to 30 miles away at maximum visual acuity given optimal conditions. Humans can also hear the ticking of a watch from 20 feet away.

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