A new paper on language and number cognition is in press: Michael C. Frank, Daniel L. Everett, Evelina Fedorenko, & Edward Gibson, "Number as a cognitive technology: Evidence from Pirahã language and cognition", Cognition (in press 2008). Michael put the paper on his web site, and so you can easily get and read the whole thing.
The abstract, like the whole paper, speaks for itself:
Does speaking a language without number words change the way speakers of that language perceive exact quantities? The Pirahã are an Amazonian tribe who have been previously studied for their limited numerical system [Gordon, P. (2004). Numerical cognition without words: Evidence from Amazonia. Science 306, 496–499]. We show that the Pirahã have no linguistic method whatsoever for expressing exact quantity, not even ‘‘one.” Despite this lack, when retested on the matching tasks used by Gordon, Pirahã speakers were able to perform exact matches with large numbers of objects perfectly but, as previously reported, they were inaccurate on matching tasks involving memory. These results suggest that language for exact number is a cultural invention rather than a linguistic universal, and that number words do not change our underlying representations of number but instead are a cognitive technology for keeping track of the cardinality of large sets across time, space, and changes in modality.
For background on issues of language, culture and numbers among the Pirahã, you might want to read "One, two, many — or 'small size', 'large size', 'cause to come together", 8/20/2004; "Life without counting throwing", 8/12/2004; "The straight ones: Dan Everett on the Pirahã", 8/26/2004; "On counting and throwing", 8/27/2004; "Language, thought and counting in Amazonia", 10/30/2004.
I have only one additional comment for now. From a historical point of view, the first sentence of Frank et al.'s abstract asks the question backwards:
Does speaking a language without number words change the way speakers of that language perceive exact quantities?
This is the right question from the perspective of cognitive psychologists who are used to working with people who speak languages with number words, and now have the opportunity to learn about number cognition among speakers of a numberless language. But from the point of view of cultural evolution, the question goes in the other direction: did developing languages with number words change the way that people perceive exact quantities? As I understand the answer proposed by Frank et al., it's "no, the basic representation remains the same, or at least some aspects of it do; what changes is mainly the ability to remember and compare".
But I'd like to point out that comparing exact quantities is only one aspect of the way that people "perceive exact quantities". Once the "cognitive technology" of number is established, there are many other properties of particular exact quantities, or classes of exact quantities, that may become cognitively salient.
Once, a five-year-old of my acquaintance, stimulated by kindergarten exercises in counting and comparing, announced a discovery: there are a "fair numbers" and "unfair numbers". Fair numbers, he explained, are when if you have that many things, you can share them with a friend so that you each have the same. With unfair numbers, somebody always gets more. (This was not part of the lesson plan — in fact, I learned about it because his teacher perceived his enthusiasm for unscheduled discoveries, expressed in idiosyncratic terminology, as distracting and even disruptive.)
After you've understood something like the distinction between even and odd numbers, it seems to me that it becomes (to one degree or another) part of the way that you "perceive exact quantities". The set of such properties is indefinitely large, and most people don't become familiar with as many of them as Ramanujan famously did; but still…
[Also relevant here are some of the abstracts from a 2004 workshop on Numerals In the World's Languages: William McGregor, "Numerals in Australian languages"; Pattie Epps, "Tracing the development of numerals in the Guaviaré-Japurá (Maku) family"; Dan Everett, "On the absence of number and numerals in Pirahã"; Heike Wiese, "Language and the emergence of recursivity in the numerical domain". When I have time, I'll try to track down the full form of these.]