Hi tuesday,

"the way we see things now can be assumed to be the way things have always been seen - particularly the imagining of three dimensional objects"

2500bc isn't all that far away tuesday, twice the Romans.
Possibly more use of one side of the brain than the other - writing, calculative/creative, but no more than we can see today, like Japanese - European.

I think that the idea is that at a certain period in time a combination of mem factors and social factors gave the capability to build complexer societies, but this would have been much earlier than 2500bc.

7000bc bullae.
3200bc pictograms mnemotechnical device Mesopotamia.
3000bc phonetic writing.
2600bc first literature.
It would seem that calculi and imaging predated writing, the book Ancestors of the West does mention conveying messages in combination of numbers like 'After rain comes sunshine - 9'. something like this anyway.

There are quite a few interesting studies on these topics, well worth reading.