A model of the visual pathways it has been developed consisting of two neural systems working together: a feed-forward mechanism given by convolutions through different layers and a feed-back one consiting of the comparison of the results of the first one. The first mechanism would be predominant at lower centers, and it would be able, for example, to explain the increase in contrast sensitivity at different stations of visual pathways. The second mechanism seems apter to explain the behaviour of complex and hypercomplex cells whose activity is to a great extent independent of the position of the stimulus in the receptive field. The ideas developed in this paper could have some implications for building a machine able to recognize patterns independently of their position.