I believe that you are asking if on a Parent record to see a summary of the details in text information from child records (the children here are your Join table records) . There is not currently a Summary text type fields where you can roll up the children into a long text field.
However, using a technique called reverse relationships you can float up the data contained in a limited number of child records up to the parent.
Can you tell me what the reasonable number of children you need to flow up is. Note that you can also have a message that tells the user that there are more.
I will post an additional response with how to do reverse relationships.
