Abstract
When decisions are made under speed pressure, “urgency” signals elevate neural activity toward action-triggering thresholds independent of the sensory evidence, thus incurring a cost to choice accuracy. While urgency signals have been observed in brain circuits involved in preparing actions, their influence at other levels of the sensorimotor pathway remains unknown. We used a novel contrast-comparison paradigm to simultaneously trace the dynamics of sensory evidence encoding, evidence accumulation, motor preparation, and muscle activation in humans. Results indicate speed pressure impacts multiple sensorimotor levels but in crucially distinct ways. Evidence-independent urgency was applied to cortical action-preparation signals and downstream muscle activation, but not directly to upstream levels. Instead, differential sensory evidence encoding was enhanced in a way that partially countered the negative impact of motor-level urgency on accuracy, and these opposing sensory-boost and motor-urgency effects had knock-on effects on the buildup and pre-response amplitude of a motor-independent representation of cumulative evidence.
Highlights
When decisions are made under speed pressure, “urgency” signals elevate neural activity toward action-triggering thresholds independent of the sensory evidence, incurring a cost to choice accuracy
Urgency signals may first confluence with evidence at downstream motor levels, allowing an unadulterated representation of cumulative evidence to be retained at the motor-independent level
Subjects reported whether the left- or right-tilted lines in a compound overlaypattern had a greater contrast by pressing a button with the thumb of the corresponding hand (Fig. 1a)
Summary
When decisions are made under speed pressure, “urgency” signals elevate neural activity toward action-triggering thresholds independent of the sensory evidence, incurring a cost to choice accuracy. Prominent computational models suggest that sensorimotor decisions are made by integrating noisy evidence representations up to an action-triggering threshold or bound[1,2]. In this framework, speed can be emphasized at the expense of accuracy by lowering this bound[3,4]. Motor-selective neural circuits have been found to implement such adjustments in the form of evidence-independent “urgency” signal components, which non-selectively elevate activity towards unchanged action thresholds. Urgency signals may first confluence with evidence at downstream motor levels, allowing an unadulterated representation of cumulative evidence to be retained at the motor-independent level
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