From the introduction, "This study was undertaken to determine which phones would be interpreted as the same and which as different by non-literate native speaker of the Kogi language."
Stendal, Patricia C.
"Psycho-linguistic approach in Kogi phonemes,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 12, Article 3.
Available at: https://commons.und.edu/sil-work-papers/vol12/iss1/3