science & techanalysisThe Conversation: Arts + Culture (US)
How primate eye tracking reveals new insights into the evolution of language
Apes and humans watch social scenes in almost the same way, tracking who acts and who receives the action as the scene unfolds. In eye-tracking tests with zoo chimpanzees, gorillas and orangutans, their gaze alternated between the doer and the target, just as adults' did. Human infants did not do this yet and mostly looked at the background, suggesting the skill develops with experience. The ability to split events into agent and patient is therefore older than language, and language likely built on it. Apes do not yet describe such events in sentences the way people do, which remains an open question.
Infrared eye trackers record where a viewer's gaze falls on a screen, so researchers can see which part of a scene draws attention over time. Participants watched short videos of social actions, such as one animal embracing another, and non-social actions, such as a person pushing a shelf. Comparing gaze patterns across adults, infants and apes shows which cues guide attention.
Grammar's basic structure of who did what to whom may rest on a cognitive habit shared with our closest relatives. That reframes language as an extension of ancient social perception rather than a purely human invention. It helps explain why the subject-action-object pattern is so common across the world's languages.
Many cognitive building blocks of language, such as tracking objects, faces and intentions, appear in other primates in rudimentary form. Researchers see language as built on older social abilities rather than arriving fully formed. Comparative studies of this kind have shifted the field toward continuity between humans and other apes.
The Conversation
Illustrative photo · Naomi Nota, CC BY-SA 2.0, via Wikimedia Commons
