As part of a task in a psychological experiment I have a "transformation table" that contains two rows of letters:
A B C D ... Z R K Q ...
The participants are given a selection of letters (e.g. "B") and must transform them with the help of this table (e.g. "B" into "R").
To explain this procedure there is an example that gives a sample letter and a sample transformation, e.g.:
... result B R
The text above the two letters should explain that the "B" is the letter that is given to the participants as "source material" or "input", and that the "R" is the result after the transformation.
What is the noun that describes the stimulus given in an experiment?
The verb used in this situation is "given", but there appears to be no noun with the corresponding meaning, since the noun "given" means something quite different, namely "a basic condition or assumption" (Merriam-Webster). And it is not a "prompt", because a prompt is not material to be processed.
The original German word I am translating this from is "Vorgabe". In this context it means "something that is given".