Separating decision and motor contributions to behavioral biases induced by manipulating stimulus probability
Edouard Dendauw1, Gordon D Logan2, Jeffrey D Schall3
1Laboratoire de Recherches Intégratives en Neurosciences et Psychologie Cognitive, Institut National de la Santé et de la Recherche Médicale, Université Marie et Louis Pasteur, France.
Cognitive Psychology
|June 11, 2026
Summary
Stimulus probability influences decision-making and motor control by altering evidence accumulation and motor preparation timing. This research clarifies how expected stimuli speed up responses, impacting both accuracy and muscle activity.
Area of Science:
- Cognitive Neuroscience
- Computational Neuroscience
- Human Motor Control
Background:
- Stimulus probability effects on behavior are known, but their neural underpinnings, particularly at the motor execution stage, are unclear.
- Sequential sampling models explain some effects via evidence accumulation, yet motor-level modulations require further investigation.
Purpose of the Study:
- To investigate how stimulus probability influences motor execution and its relationship with upstream decision processes.
- To differentiate the impact of stimulus probability on evidence accumulation versus motor preparation and execution.
Main Methods:
- Electromyography (EMG) recorded muscle activity during a random dot motion task with varied stimulus probability and discriminability.
- A gated cascade diffusion model computationally linked decision and motor processes to behavioral and EMG data.
Main Results:
- Stimulus probability modulated the timing of muscle onsets, with earlier onsets for expected stimuli on correct trials and later on incorrect trials.
- The time from muscle activation to response completion was minimally affected by stimulus probability.
- Subthreshold muscle activations revealed accuracy differences based on the timing of initial muscle activity relative to stimulus expectation.
Conclusions:
- Stimulus probability influences cognitive processing through both an additive bias in evidence accumulation and an urgency signal in motor preparation.
- These findings elucidate the interplay between decision-making and motor control across the entire processing cascade.
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