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After their successful employment in nerve and muscle research, microelectrodes are widely used to explore impulse activity in various parts of the brain and spinal cord. As part of this work, the sensory receiving areas of the cerebral cortex are found to be organized in columns of neurons, just as Lorente de Nó had predicted many years earlier. Experiments by David Hubel and Torsten Wiesel demonstrate that cells in the visual cortex respond to lines and edges, rather than spots and circles, in the visual field. The same workers demonstrate the functional plasticity of the developing visual cortex. Glass micropipettes are used for the iontophoretic application of drugs to neurons and in this way a number of new neurotransmitters are discovered. Because of the huge amount of new knowledge, the last decades of the 20th century are a golden age for neuroscientists, and for neurophysiologists in particular. Since then a number of problems have arisen, for which various solutions have been adopted.

David H. Hubel was born in Windsor, Ontario, Canada, to American parents in 1926. In 1929, his family transferred to Montreal where he was brought up and educated and continued to live until the age of 28. He attended Strathona Academy until his graduation in 1943. Given that he ended up as a biologist, it was ironic that he had almost no formal instruction in biology in grade school, high school, or college. He studied mathematics and physics at McGill University, and later entered medical school there. After graduating from medical school, he did a rotating internship at Montreal General Hospital. He was married in June 1953 to Ruth. In 1954, he moved to the United States to work at Johns Hopkins University School of Medicine and later served at Walter Reed Hospital. In 1958, he went back To Baltimore and began his collaborations with Torsten Wiesel.

This chapter describes the novel findings of David Hubel and Torsten Wiesel when recording from single cells in the primary visual cortex and how these findings supported the concept that the various features of the observed image underwent independent processing in parallel. Of the various sensory systems, the one about which most is known is the visual one. Vision is also the most complex sensory system, which is reflected in its large cortical territory. The chapter thus focuses on the sense of sight in particular as it explores the findings of Hubel and Wiesel. However, the chapter also presents an alternative to the now-classic Hubel–Wiesel scheme, one that, despite its fundamental differences, seems equally plausible.

In Chapter 3 we saw that non-relational theories assume a coloring in model. Anti-realists imagine that achromatic reality is falsely colored by the projections of the mind, while realists take colors to be intrinsic properties of objects that are detected independently of our responses to other visible stimuli. Both realists and anti-realists disregard the interactions between color perception and other visual functions. Crucially though, the coloring in model does not mesh with empirical findings about the various uses of color vision, and the influence of perceptual context on perceived color. This chapter presents the case for the alternative to the coloring in model. Inspiration comes from the scientific results showing that color vision is not separate or separable from the rest of vision; instead it serves many tasks that are integrated with various visual functions such as perceiving depth and shape. Coloring-in is replaced by coloring-for. Color vision should not be thought of as a means of seeing color, but as a way of seeing things.

In this chapter, the author focuses on Leon Glass's discovery of a set of unexpected visual stimuli that led to an additional understanding of the physiology of visual perception. He discusses the work done by other scientists by building on the Glass patterns, particularly David Marr, a neuroscience theorist who presented Glass's random dot moiré patterns as a perceptual illusion that required integrative features of the visual system as well as a challenge to be solved. He also considers the experiment performed by David Hubel and Torsten Wiesel on the hypercolumn, a set of neurons that tile the primary visual cortex with a cell for every location and every orientation. This tiling of the cortex by orientation is the key to the biological interpretation of the Glass patterns.

In this chapter, the author offers a critique of pure cortical topography, with particular reference to the retinotopic map as a key principle used to unlock the function of the cerebral cortex. He first discusses the properties that are embedded within retinotopic maps, along with the idea of the functional architecture proposed by David Hubel and Torsten Wiesel and their demarcation of a whole series of mappings in the primary visual cortex. He then considers constant sensory representations in relation to the idea that the internal cortical representations are fixed and hard wired. He also describes his work on “navigational motion” in collaboration with Milena Raffi and concludes by noting that the functional architecture of the inferior parietal cortex is constantly modified in response to the changing internal and external world.

In this chapter, the author reflects on Vernon Mountcastle's work on cortical organization and his salt-and-pepper view of association cortex. He first describes the study that he and Milena Raffi carried out regarding attentional maps in the parietal cortex and their extension of the idea of a wiring diagram for cortical organization. He then considers the experiments performed by Stephen Kuffler, David Hubel, and Torsten Wiesel on the structures in the primary visual cortex, along with Gordon Holmes's discovery of the retinotopic map. Finally, he discusses Daniel Felleman and David Van Essen's connectional diagram.