The starting point is that our brain was (probably) more or less as today, hence in principle capable of cognitive tasks of similar "quality" or complexity. But

The starting point is that our brain was (probably) more or less as today, hence in principle capable of cognitive tasks of similar "quality" or complexity. But there is no doubt that what these capabilities were applied to might feel very exotic or even uncomfortable to us. E.g., Graber makes this point in particular in relation to social relations. A lot of modern society would probably look like totally brain damaged to them in terms of emotional / social intelligence. We have also the examples of very elaborate religious / theological discourse, which seems to have been a major preoccupation for the longest time. On the other hand there are definitely cultural inflection points (like writing or numeracy) that seem to have reshaped the ability of a trained brain in a very short period of time. E.g. if you compare writings from the same civilization / region just several hundred years apart (Homeric poems vs Classic Athenian philosophy) its hard to believe its even the same species...