Non-Human Recognition of Orthography: How is it implemented and how does it differ from Human orthographic processing

Abstract

The ability to robustly recognize strings of letters, a cornerstone of reading, was observed in Baboons and Pigeons despite their lack of phonological and semantic knowledge. Here, we apply a comparative modeling approach to investigate the neuro-cognitive basis of Human, Baboon, and Pigeon orthographic decision behavior, addressing whether phylogenetic relatedness entails similar underlying neuro-cognitive phenotypes. We use the highly transparent Speechless Reader Model (SLR), which assumes letter string recognition based on widely accepted computational principles of predictive coding so that orthographic decisions rely on a prediction error signal emerging from multiple, hierarchically ordered representational levels, i.e., low-level visual, letter, or letter sequence representations. We investigate which representations species use during successful orthographic decision-making. We introduce multiple SLR variants, each including one or multiple prediction error representations, and compare the simulations of each SLR variant to the orthographic decisions from individuals of three species after learning letter strings without meaning. Humans predominantly relied on letter-sequence-level representations, resulting in the highest task performance in behavior and model simulations. Baboons also relied on sequence-based representations but in combination with pixel- and letter-level representations. In contrast, all Pigeons relied on pixel-level representations, partly in combination with letter- and letter-sequence-level representations. These findings suggest that orthographic representations utilized in orthographic decisions reflect the phylogenetic distance between species: Humans and Baboons use more similar representations compared to Pigeons. Overall, the description of orthographic decisions based on a small set of representations and computations was highly successful in describing behavior, even for Humans who mastered reading in its entirety.Significance StatementImagine being able to read without ever learning the alphabet. Research has shown that baboons and pigeons can exhibit reading-like behavior, suggesting shared processes across the species involved. To increase our understanding of the similarities and differences between humans and animals in reading-like behavior, we use a computational model to uncover the underlying processes that enable humans, baboons, and pigeons to perform these tasks. We found that humans and baboons rely on similar processes, focusing on information related to letters and letter sequences. In contrast, pigeons rely more heavily on visual cues. This discovery sheds light on the evolution of processes underlying reading and reading-like behavior, indicating that the lower the evolutionary distance between species, the more similar processes are involved.