This paper explores turtle visual cortex, in an area known as dCx. This dorsal region plays the role of the turtle primary vision center — as close as you can find to the homolog of human V1.
But unlike V1, Fournier & Müller et al confirm the existing knowledge that while dCx receives direct inputs from LGN, its layout is not retinotopic.
In particular, they noticed that certain cells of dCx responded to scene-level stimuli: When there was a cut, or the film started or stopped, there was a burst of activity. When the same stimulus was played repeatedly, these responses died away.
This style of scene-level parsing in mammals is reserved for “later”, down-stream brain areas. Does this mean that turtles are using dCx as both early signal processing as well as higher-level object recognition and interpretation? If so, does this mean that mammalian brains, with discrete areas for low-level and high-level vision, evolved from an earlier system where all of these tasks were colocated?