1. Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, 49 Convent Drive, Bethesda, Maryland 20892, USA

Correspondence to: Hendrikje Nienborg¹ Correspondence and requests for materials should be addressed to H.N. (Email: hnienb@gmail.com).

Abstract

During perceptual decisions, the activity of sensory neurons correlates with a subject's percept, even when the physical stimulus is identical^{1, 2, 3, 4, 5, 6, 7, 8, 9}. The origin of this correlation is unknown. Current theory proposes a causal effect of noise in sensory neurons on perceptual decisions^{10, 11, 12}, but the correlation could result from different brain states associated with the perceptual choice¹³ (a top-down explanation). These two schemes have very different implications for the role of sensory neurons in forming decisions¹⁴. Here we use white-noise analysis¹⁵ to measure tuning functions of V2 neurons associated with choice and simultaneously measure how the variation in the stimulus affects the subjects' (two macaques) perceptual decisions^{16, 17, 18}. In causal models, stronger effects of the stimulus upon decisions, mediated by sensory neurons, are associated with stronger choice-related activity. However, we find that over the time course of the trial these measures change in different directions—at odds with causal models. An analysis of the effect of reward size also supports this conclusion. Finally, we find that choice is associated with changes in neuronal gain that are incompatible with causal models. All three results are readily explained if choice is associated with changes in neuronal gain caused by top-down phenomena that closely resemble attention¹⁹. We conclude that top-down processes contribute to choice-related activity. Thus, even forming simple sensory decisions involves complex interactions between cognitive processes and sensory neurons.

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