The smallest possible difference between two stimuli that can be detected is called the:

The just noticeable difference

Explanation:The just noticeable difference (JND), which is also referred to as difference threshold.

This is a minimum stimulation level we can be able to detect half of the time.

For example let us say you were carrying two buckets which has different weights , for you to notice half of the time the minimun difference in their weights that is Just noticeable difference.

the 4th option is the answer

i would say b. research typically uses a variety of sources