September 2015
Volume 15, Issue 12
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2015
Motor-evoked potentials reveal a motor-cortical readout of evidence accumulation for sensorimotor decisions
Author Affiliations
  • Kielan Yarrow
    Department of Psychology, City University London
  • Aviad Hadar
    Department of Psychology, City University London Department of Life Science, Ben-Gurion University
  • Paula Rowe
    Department of Psychology, City University London
  • Steven Di Costa
    Institute of Cognitive Neuroscience & Department of Psychology, UCL
  • Alex Jones
    Department of Psychology, Middlesex University
Journal of Vision September 2015, Vol.15, 49. doi:10.1167/15.12.49
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      Kielan Yarrow, Aviad Hadar, Paula Rowe, Steven Di Costa, Alex Jones; Motor-evoked potentials reveal a motor-cortical readout of evidence accumulation for sensorimotor decisions. Journal of Vision 2015;15(12):49. doi: 10.1167/15.12.49.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Many everyday activities, such as driving and sports, require us to engage in time-pressured sensorimotor decision making in response to visual cues. The computational principle of continuous evidence accumulation is the dominant account underlying models of speeded decision making, but the nature and locus of the decision variable that triggers action is debated. Traditionally, cognitive stages such as perception, stimulus-response translation, and the generation of motor plans, have been considered to occur in series. However, this idea is challenged by neurophysiological work in animals, suggesting that cognitive operations are distributed across sensorimotor cortex. Here, we investigate whether a decision variable can be observed in the primary motor cortex (M1) of humans. Participants categorised faces as male or female, with task difficulty manipulated using natural or morphed stimuli. Transcranial magnetic stimulation, applied at random across the reaction-time interval, produced motor-evoked potentials (MEPs) in two hand muscles that were the major contributors when generating the correct and incorrect pinch/grip movements. MEP magnitudes reveal covert action preparation, even when no action is produced. Smoothing MEPs using a Gaussian kernel allowed us to recover a continuous time-varying MEP average, comparable to an EEG component, which permitted precise localisation of the time at which the motor plan for the responding muscle began to dominate over the non-responding action. This moment was calculated in both stimulus-locked and response-locked analyses, and was found to occur at the same time with stimulus locking, but earlier with response locking, when ambiguous stimuli made the decision more challenging. This pattern is consistent with M1 providing a continuous readout of evidence accumulation. We predicted the evidence accumulation profile from a drift diffusion model, using only behavioural data, and found a good qualitative match to the observed neurometric MEP profiles.

Meeting abstract presented at VSS 2015

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