Reaction-time asymmetry covaries with shifts in hand choice in macaques

Reaction time peaks near the hand-choice transition point (PSE) in two male Macaca mulatta, and the PSE shifts with head, gaze, and hand-displacement manipulations.

• Why it matters: Prior monkey work used only two targets, limiting psychometric modeling, and it remains unclear whether reaction time tracks the same choice boundary seen in humans.
• What they did: They measured free hand choice across ten horizontal target positions in two male rhesus macaques, then tested how displacing hands, rotating head, or displacing gaze shifted the PSE and reaction-time patterns.
• The result: Reaction time was longest near the PSE, and in every condition the farther the PSE toward one side, the slower that side’s hand relative to the other, supporting macaques as a model of human-like hand choice.

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