---
type: source
id: steckenfinger-ghazanfar-2009
title: Monkey visual behavior falls into the uncanny valley
authors:
- Shawn A. Steckenfinger
- Asif A. Ghazanfar
year: 2009
venue: Proceedings of the National Academy of Sciences (PNAS)
volume: 106(43)
pages: 18362-18366
doi: 10.1073/pnas.0910063106
peer_review: peer-reviewed-journal
evidence_tier: B
design: Looking-time preference in macaque monkeys for real, realistic-synthetic, and unrealistic-synthetic monkey faces
modality:
- image-face
- non-human-primate
stimuli: Real monkey faces; realistic and unrealistic synthetic monkey faces
n_participants: 5
n_note: macaques (approximate)
topics:
- uncanny-valley
- evolution
summary: Macaques looked less at realistic synthetic faces than at real or unrealistic ones—an uncanny-valley analogue in another species.
results:
- metric: Looking time
  value: realistic-synthetic < real and < unrealistic
  note: ''
  source_location: null
moderators: []
limitations:
- Very small N
- Looking time is an indirect aversion proxy
mechanism_supported:
- evolved-perceptual-basis
verification:
  status: unverified
  confidence: high
  checked: null
  via: compiler knowledge
url: null
pmid: null
pmcid: null
arxiv_id: null
openalex_id: null
oa_url: null
cited_in:
- MR-0002
updated: '2026-10-07'
---

# Monkey visual behavior falls into the uncanny valley

> **Source record** `steckenfinger-ghazanfar-2009` · 2009 · Proceedings of the National Academy of Sciences (PNAS)  
> **Evidence tier:** B (peer-reviewed-journal) · **Verification:** unverified (compiler confidence: high)  
> **Bottom line:** Macaques looked less at realistic synthetic faces than at real or unrealistic ones—an uncanny-valley analogue in another species.

## Citation {#citation}

Shawn A. Steckenfinger, Asif A. Ghazanfar (2009). Monkey visual behavior falls into the uncanny valley. *Proceedings of the National Academy of Sciences (PNAS)*, 106(43), 18362-18366. https://doi.org/10.1073/pnas.0910063106

Verification entry (identifiers, resolvers, claims with source locations): [/data/citations.json#steckenfinger-ghazanfar-2009](/data/citations.json#steckenfinger-ghazanfar-2009)

## Study design {#design}

| Field | Value |
|---|---|
| Design | Looking-time preference in macaque monkeys for real, realistic-synthetic, and unrealistic-synthetic monkey faces |
| Modality | image-face, non-human-primate |
| Stimuli | Real monkey faces; realistic and unrealistic synthetic monkey faces |
| Participants (N) | 5 |
| N detail | macaques (approximate) |
| Topics | uncanny-valley, evolution |

## Results {#results}

| Metric | Value | Note |
|---|---|---|
| Looking time | realistic-synthetic < real and < unrealistic |  |

## Mechanism relevance {#mechanism}

`evolved-perceptual-basis`

## Limitations {#limitations}

- Very small N
- Looking time is an indirect aversion proxy

## Cited in {#cited-in}

- [MR-0002](/metareports/uncanny-valley-and-synthetic-faces.md): The Uncanny Valley and Synthetic Media: Does It Exist, What Causes It, and Have Deepfakes Crossed It?

## Verification {#verification}

| Field | Value |
|---|---|
| Status | `unverified` |
| Compiler confidence | high |
| Checked on | — |
| Via | compiler knowledge |

Values on this page have not all been checked against the full text. Confirm them against the primary source before high-stakes use.