Motor effort biases perceptual decisions through later-stage evidence accumulation rather than early sensory-attentional processing

A recent study explored the influence of motor effort on perceptual decision-making, aiming to determine whether this bias occurs during the initial stages of decision formation or later in the process. The researchers recorded the brain activity of twenty-four healthy adults as they performed an orientation discrimination task using EEG.

In this task, two Gabor patches were presented simultaneously to the left and right visual hemifields, and participants indicated their decisions using two pressure-sensitive buttons with varying levels of force.

The findings revealed that motor effort had an impact on neural processing at both the preparatory and later stages of decision-making. Pre-stimulus alpha power was found to be reduced over the occipito-parietal cortex on the side corresponding to the low-effort option. Additionally, mean centro-parietal positivity (CPP) amplitude, which appeared before response execution, was greater for low-effort choices compared to the high-effort option.

However, these changes in CPP amplitude were not linked to any behavioral decision bias. Furthermore, the study observed that trial-by-trial CPP amplitude preceding response execution increased when participants were more likely to choose the low-effort option, suggesting that motor effort biases perceptual decisions primarily during the later stages of evidence accumulation.

The researchers concluded that this bias provides insight into the neural basis of embodied perceptual decision-making, emphasizing the role of motor effort in shaping perceptual choices.