In ASL spatial classifier expressions, the location of the hands in signing space depicts the relative position of described objects. When objects are physically present, the arrangement of the hands maps to the observed position of objects in the world (Shared Space). For non-present objects, interlocutors must perform a mental transformation to take the signer's perspective ("Signer Space"). The ASL Spatial Perspective Comprehension Test (ASPCT) was developed to assess the comprehension of locative expressions produced in both Shared and Signer Space, viewed from both canonical Face-to-face and 90° offset viewing angles. Deaf signers (N = 38) performed better with Shared than Signer Space. Viewing angle only impacted Signer Space comprehension (90° offset better than 180° Face-to-face). ASPCT performance correlated positively with both nonverbal intelligence and ASL proficiency. These findings indicate that the mental transformation required to understand a signer's perspective is not automatic, takes time, and is cognitively demanding.