Although this phenomenon has been known for decades, how sensory information is encoded in the brain in the absence of awareness to influence subsequent sensory processing across neural circuits has remained a mystery. Nonetheless, they can facilitate the perceptual processing of the same stimuli in a subsequent behavioral task 1, 2, 3, 4, 5, 7, 8, 9, 10, 11. Perceptual studies have revealed that masked stimuli presented below the visibility threshold do not elicit conscious perception as they cannot be recognized or even guessed above chance on a force-choice test 1, 2, 3, 4, 5, 6. For instance, when an image is presented in close spatiotemporal proximity with other stimuli it becomes invisible, a perceptual phenomenon called masking. However, whether stimuli below the limit of awareness can influence brain responses to bias behavioral decisions is unknown. The relationship between brain activity and behavior has been traditionally investigated by measuring the responses of neurons to stimuli presented above the detectability threshold. This form of unsupervised adaptation may constitute a vestigial pre-attention system using the mere frequency of stimulus occurrence to change stimulus representations even when sensory inputs are perceptually invisible. This phenomenon is consistent with a Hebbian mechanism underlying an increase in functional connectivity specifically for the neurons activated by subthreshold stimuli. Such exposure increases stimulus sensitivity and information encoded in cell populations, even though animals are unaware of stimulus identity. Here, we recorded populations of neurons in macaque primary visual cortex (V1) to find that perceptually unidentifiable stimuli repeatedly presented in the absence of awareness are encoded by neural populations in a way that facilitates their future processing in the context of a behavioral task. Although the neural bases of conscious experience have been extensively investigated over the past several decades, how unconscious information impacts neural circuitry and behavior remains unknown. Our daily behavior is dynamically influenced by conscious and unconscious processes.
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