![]() Natural scenes were rendered indistinguishable by embedding them into a 1600-ms movie, consisting of random oriented gratings flashed at 60 Hz 14, 15, 16. We demonstrate that exposure to unidentifiable stimuli presented below the threshold of perception changes stimulus representation as early as primary visual cortex to influence behavioral performance specifically for the stimuli being exposed.ĭesigning perceptually unidentifiable stimuli ![]() We address these issues for the first time by recording neural population activity in macaque primary visual cortex (V1) using multiple electrodes to examine whether perceptually unidentifiable stimuli influence the coding of information in visual cortex and perceptual performance. Previous electrophysiological experiments in monkey V1 13 have reported that firing rates of individual cells are strongly reduced when forward and backward masks are combined, but whether and how exposure to such masked stimuli alters stimulus representation and subsequent perceptual performance has not been investigated. In light of this evidence, it has been proposed that the locus of subliminal priming is at an intermediate stage in the ventral cortical pathway for shape recognition, not in early visual cortex 1, 6, 11. ![]() In addition, functional MRI recordings have revealed that perceptually invisible information can be briefly maintained at the higher processing stages of visual perception 12, but not in early cortical areas. Furthermore, functional imaging studies in humans using masked words have revealed that subliminal stimuli activate higher-order fusiform and precentral brain areas 6. Previous psychophysics experiments have suggested that subliminal visual priming may be mediated by higher brain areas, possibly at or beyond the anterior part of the inferior temporal cortex 11. Specifically, do weak, subliminal stimuli unconsciously activate neuronal networks involved in perception such as to change sensory representations when stimuli are subsequently presented above the detectability threshold? 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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