Let's look at this report:

Neanderthals' keen vision may explain why they couldn't cope with environmental change and died out, despite having the same sized brains as modern humans, new research suggests.

The findings, published today (March 12) in the journal Proceedings of the Royal Society B, suggest that Neanderthals developed massive visual regions in their brains to compensate for Europe's low light levels. That, however, reduced the brain space available for social cognition.

"We have a social brain, whereas Neanderthals appear to have a visual brain," said Clive Gamble, an archaeologist at the University of Southampton, who was not involved in the study.

If one reads Gazzaniga's latest book, Who's In Charge, they will find this interesting piece of informaiton: Only 19 percent of the neurons in the human brain are located in the cerebral cortex, and the vast majority of the neurons, 72 percent, are located in the cerebellum. The cortex is responsible for "human thought and culture"; the cerebellum for "refining motor control." And it breaks down even further:

The frontal lobes and prefrontal cortex—the part of the human brain that is involved with memory and planning, cognitive flexibility, abstract thinking, initiating appropriate behavior and inhibiting inappropriate behavior, learning rules, and picking out relevant information perceived through the senses—have vastly fewer neurons than the number in the visual areas, the other sensory areas, and the motor areas
of the cortex...

With that in mind...

Neanderthal skulls suggest that the extinct hominids had elongated regions in the back of their brains, called the "Neanderthal bun," where the visual cortex lies.

"It looks like a Victorian lady's head," Robin Dunbar, an evolutionary psychologist at the University of Oxford told LiveScience.

Anatomically modern humans, meanwhile, evolved in Africa, where the bright light required no extra visual processing, leaving humans free to evolve larger frontal lobes.