Skip to content

Macaques Reacted Slowest Where Either Hand Was Equally Likely to Be Chosen

Research · Behaviour

People generally reach for a target with the hand on the same side of the body, but that preference can shift with the effort required to reach and with head or gaze direction. To test whether macaques show a similar pattern, and whether reaction time tracks hand choice, researchers studied two male rhesus macaques (Macaca mulatta) in a 2026 bioRxiv preprint.

The macaques freely chose a hand as targets appeared at ten positions across the horizontal field. For targets well to either side of the body’s midline, both animals usually used the hand on the target’s side. Between those positions, their choices shifted from one hand to the other. The transition point—where either hand was equally likely to be chosen—is called the point of subjective equality, or PSE.

Reaction times were longest near the PSE. Displacing a hand, rotating the head or shifting gaze to one side each moved the PSE toward that side. The effects on reaction time depended on the manipulation: displacing a hand slowed the macaques’ responses when they used that hand, while shifting gaze to one side slowed responses by the opposite hand. Across all conditions, the farther the PSE shifted toward one side, the slower that side’s hand was relative to the other.

This resemblance between macaque and human hand choice suggests that macaques could help researchers investigate how the brain selects a hand for reaching. The study measured choices and reaction times, not neural activity, and its findings are based on two animals.

Sources and image credit

  1. Reaction-time asymmetry covaries with shifts in hand choice in macaquesPrimary preprint. The accessible abstract reports the study sample, reaching task, manipulations and principal behavioral results.

Image: Two rhesus macaques (Macaca mulatta) sit closely together in a leafy tree. Photo: (c) Mark Clarke, some rights reserved (CC BY) / iNaturalist; CC BY 4.0. Representative photograph. · CC BY 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Behaviour

SPECIES IN THIS STORY

Species in this story

Rhesus Macaque Macaca mulatta Explore species

Independent research and conservation news archive

Did you find this information useful?

Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.

Support Wildlife Vagabond

The news archive will remain freely available.