Answer:
Case study
Explanation:
The options for this answer are:
A case study is a type of study usually used in social sciences. It consists in an intensive study about a person or a group of persons, this study is based on in-depth observations of the person or group and it aims to obtain more information about the subject of observation.
In this example, there's an individual with an exceptional memory. Therefore, a psychologist conducts an in-depth investigation of this person. We can see that the two main characteristics of the case study: in-depth investigation of an specific person are in this example and therefore the research method used would be a Case study.