Language Comprehension in Ape and Child by E. Sue Savage-Rumbaugh, Jeannine Murphy, Rose A. Sevcik, Karen E. Brakke, Shelly L. Williams, Duane M. Rumbaugh, 1993, Box: 10, item: 20. Personal Papers of Richard Schiefelbusch, PP 458. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/266528 Accessed March 12, 2025.