Occurence: The Incredible Hulk #370

The Hulk and Sub-Mariner are at Docter Strange's house and the Hulk asks Subby about Dr. Strange laying on the floor but Subby doesn't see him. That's when the Hulk realizes that it is actually the astral form of Dr. Strange and that only he can see him when he is in astral form. It was theorized before that the Hulk gave himself the ability to see all astral forms so taht he could see his dead father if he ever came back in spirit form.

Hulk's Extra-Sensory Abilities

Incredible Feats of the Hulk Main Page