A visible difference

Thirty years ago I was a young postdoc working with Larry Weiskrantz at the Department of Experimental Psychology in Oxford. The laboratory (or cubbyhole) where I worked was some distance from the main department and, perhaps because of this, our little group of postdocs and graduate students developed a strong sense of camaraderie. We spent many of our lunch hours arguing science, politics and the human condition — usually in the nearby Lamb and Flag pub. New publications in visual neuroscience, particularly theoretical papers, provided much of the fodder for our discussions. One of the papers that got us worked up was Gerald Schneider’s on “Two visual systems”, which appeared in Science in 1969 [1]. The paper was remarkable partly because Schneider was a young scientist who had only just finished his PhD, but mainly because it offered a clear and apparently straightforward account of the functional differences between the two main visual pathways in the mammalian brain. Other researchers had already suggested the ancient visual pathway that runs from the eye to the midbrain in mammals has different functions from the newer visual pathway to the cerebral cortex, but it was the elegant simplicity of Schneider’s distinction between the two that resonated with many scientists — including the discussion group at the Lamb and Flag. According to Schneider, the older pathway from the eye to the midbrain enables the animal to localize a visual stimulus, whereas the phylogenetically newer pathway to the cerebral cortex enables the animal to identify that stimulus. Schneider’s evidence for this distinction came largely from his thesis work in which he showed that hamsters with lesions of the midbrain (in a structure called the optic tectum) were unable to localize visual targets, even though they could identify them, whereas hamsters with lesions in the cerebral cortex (in a region called area V1 or primary visual cortex) could localize visual targets but could not identify them. This distinction between identification and localization — often referred to as the distinction between ‘what’ and ‘where’ — was to gain wide currency over the next 20 years.