Wiktionary
n. A signal (stimulus) that originates from outside an organism.
Usage examples of "external stimulus".
The external stimulus hits the Parent, Adult, and Child of the teenager simultaneously.
Selection was to give rise to a substance that would react to every external stimulus with internal change, not only to neutralize the stimulus but to free itself from it.
If behavior is any guide, however, Vulcans respond to external stimulus in ways distinctly different from humans.
So they have invented a concept called an ego, or a will, and claim it has complete freedom of action, as though it had no previous programming or external stimulus.
An organic fatality, rising from deep inner turmoil and without any external stimulus, causes incessant depressions which stifle the elan, attacking life at its roots.
The low, very fast oscillation indicates that the patient is concentrating on an external stimulus.
It would stay that way until he chose to obliterate the colours, or until some unexpected external stimulus jarred it out of his mind and out of existence.
The problem is gettin' it activated with the sort of arbitrary external stimulus yo' wanted, sir.
Some patients need every grip on the physical world, every external stimulus, they can get.