The experiments conducted for this thesis examined the earliest stages of processing in human visual cortex. Using electroencephalographic recordings, it was observed that the first component of the visual evoked potential, the so-called C1, is affected by learning and attention. This contrasts with earlier studies which overwhelmingly reported no effects of higher cognitive processes on early visual cortex activity. It is suggested that methodological improvements such as the adaptation of stimulus parameters to the physiological characteristics of lower visual areas partly explain the new findings. Together with other recent studies, these results show that previously prevalent notions of primary visual cortex (V1) as an inflexible module for the treatment of low-level stimulus characteristics may need to be revised. The idea that V1 can act as an adaptive and flexible processor, previously based on animal studies, is thus starting to gain support from the human literature.