Lesion in primary visual cortex (V1) causes blindness in the visual field that is processed by the damaged area. Some patients with V1 lesion can unconsciously process the stimuli presented in their blind visual field. This kind of processing can be observed, for example, using a paradigm in which a patient is required to make a guess about the visual stimulus that he or she reports not seeing. If the accuracy of the responses is better than chance, it can be interpreted as unconscious processing, which is a measurable effect on behavior without conscious perception. This phenomenon of unconscious processing without V1 is commonly referred to as blindsight. The findings of unconscious processing without V1 in blindsight patients cannot be straightforwardly generalized to neurologically healthy people. Neural plasticity changes these patients’ brains; therefore, blindsight could be explained by these neural changes. Transcranial magnetic stimulation (TMS) is a method used to study the function of a cortical area in neurologically healthy people. With TMS, it is possible to interfere with the normal functioning of the brain. TMS of V1 can suppress the conscious perception of a visual stimulus. In this thesis, I studied whether the unconscious processing of visual stimuli is possible in neurologically healthy participants when the conscious perception of the stimulus is suppressed by TMS of V1. I found that both conscious and unconscious processing of visual information depend on V1 in neurologically healthy participants. Unconscious processing was observed only with the simplest task, in which participants responded to stimulus appearance. In this task, unconscious processing was observed only when the early activation of V1 was intact. The unconscious processing of chromaticity and motion was not observed when the stimulus was suppressed by TMS of V1. Therefore, I conclude that unconscious visual processing depends on V1 in neurologically healthy participants.