When you let someone know what she/he is about to do in a psychological experiment, you are providing

informed consent

Explanation:

In psychological experiment, informed consent makes sure that a research participant or patient are made aware of all likely risks and financial implications of any procedure or experiment. Participants in such experimental settings and the persons or organizations providing the funds for the research must be made aware of any harm that may come up

Participants are told why the research is being conducted and the time it will take from start to finish. They are also informed of their right to withdraw from the study if they wish to do so and they are also informed of any likely outcome of withdrawing or declining from the research.  

Those conducting the research are required to get written or verbal confirmation to document and confirm that all those taking part in the experiment have given their consent to be part of the process.  

an informed consent

Explanation:

Informed Consent

Informed consent has the obligation to make sure and provide a patient, client, and research participants are aware of all the procedures, risk factors and costs implication in a treatment or experiment. The patient receiving treatment or conducting an experiment on and the client funding it needs to be aware of any possible harm that might occur. 

For informed consent to be considered valid, the participant must be able to handle it , and the consent should be given of their free volition.

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