That's interesting. From what I understood of the article, to portray an existing object, they emit a constant sound, and the shape of the object modifies the sound which makes a unique sound (which is then transformed into an image by the receiving dolphin).
Therefore, to imagine an object they have to:
1) have the ability to create unique shape-sounds with their vocal clicks and
2a) had to have either seen/heard the shape before, OR
2b) have the ability to imagine what an imaginary object would sound like.
If research shows the way of conveying imaginary objects is 2a, that would mean dolphins are physically unable to convey abstract ideas (note: this wouldn't completely rule out abstraction, just the communication of it). If it's 2b, and they can communicate abstract concepts... that would be a monumentally profound discovery.
Therefore, to imagine an object they have to:
1) have the ability to create unique shape-sounds with their vocal clicks and
2a) had to have either seen/heard the shape before, OR
2b) have the ability to imagine what an imaginary object would sound like.
If research shows the way of conveying imaginary objects is 2a, that would mean dolphins are physically unable to convey abstract ideas (note: this wouldn't completely rule out abstraction, just the communication of it). If it's 2b, and they can communicate abstract concepts... that would be a monumentally profound discovery.