Have you had a look at demographics? Education about good health care, diet and/or consumption patterns that may alter neurodevelopment? Given the type of question it looks like you are asking I would be tempted to look into family history of consumption - ie neurodevelopment in the fetus is significantly affected by maternal alcohol and nicotine consumption. This could be linked to education about healthy living and consumption that may or may not be available to poorer participants (past and present generations).

Interesting theory Carol. Are you suggesting that there is simply more to look at in developed countries and so the occipital cortex develops to cope with increased demand? This would certainly make sense, though I don't know how you might quantify this - definitely a few covariates linked to environmental factors. Would you liken this to the evolution of the brain in social creatures (lets take primates for example), with increased size being linked to the pressures of effective communication in more developed species population?

I am certainly intrigued by your answer. However, would "stimulating" visual stimulation not be a relative concept? Whilst we have a large number of things that enter our visual system that is not to say that there is not an equal number of stimuli that warrant visual processing in underdeveloped countries. Take a rural country for example, successful evolution will likely have followed the need to identify putative aspects of the land - ie fruits, poisons, predators, potential food sources and any of the other elements that could interfere with these. This would warrant a keen eye, and so whilst the macro scale of visual stimuli is not the same as it would be in Tokyo, the attention to a possibly larger number of finer details is likely to approach a relatively similar figure - I would hypothesize as much anyway. So, this actually takes us down the route of a need for greater executive processing of the visual input. This could mean that the amount of visual stimuli available would not affect occipital cortex volume/surface area but would probably manifest in an increased density of visual signal coherences between the occipital cortex and associative cortical regions (most likely the temporal cortex). Obviously I am just presenting some speculation here, as I do believe that occipital cortex size would involve a wealth of contributing factors - you mentioned the recruitment of redundant regions, is it not going a bit far to liken reduced complexity of environmental stimuli to a loss of cortical function?

Not so difficult to test with the advent of portable eeg systems.

Perhaps the impoverished rat experiments might share some light on this subject.

Rats brought up in impoverished cages show less brain weight than rats brought up in rich environments. If the richness is in the visual range then you would expect the added weight to be in the occipital lobes.

Could it be linked to the development of walking, that is, if children walk early vs later? Walking helps a child explore the environment and could provide more opportunities for visual stimulation.

My candidate explanation would emphasize the role of novel visual imagery. Poor populations are almost fully occupied with survival tasks leaving little time for the range of visual exploration, text-induced imagery, and sheer fantasy that leisured populations enjoy. These latter kinds of cognitive behaviors actually add new synaptic patterns and neuronal components to the visual system. For more about this, see The Cognitive Brain (MIT Press 1991), Ch. 3, "Learning, Imager, Tokens, and Types: The Synaptic Matrix". An online copy is available here:

http://people.umass.edu/trehub/thecognitivebrain/chapter3.pdf

Two questions for clarification:

1) Is the occipital lobe absolutely larger or proportionally larger? In other words, are you measuring occipital lobe size in two populations independent of other volumetric measurements? Or does the occipital lobe take up a greater proportion of the total cortical volume in above-poverty populations?

2) What sulcal/gyral landmarks are being used to delineate the occipital lobe? What exactly is being measured - volume, thickness, or surface area?

The occipital lobe has many connections with other brain regions, and one needs to be careful in determining causality. The occipital lobe may be larger dependent on a number of variables, such as possible requirements by other regions for increased connectivity.

Correlational evidence could point to a link between poverty and size, however poverty does not necessarily indicate certain types of environments, educational levels etc, nor does above - poverty necessarily indicate the opposite. Factors linked to above or below poverty need to be carefully scrutinised, as does factors such as environment (for instance a person from a rural environment is visually oriented towards horizontal horizons, whilst city dweller are more visually oriented towards vertical horizons) educational level, age, gender etc. The role of different parts of the visual processing system also need to be considered. Another factor that needs to be considered are the type of tests utilised to assess the relationship between poverty and occipital lobe size. Also as other colleagues, such as Katherine has pointed out neurobiological definition of occipital size etc needs to be clarified.

The interactions between environmental factors, genetic predisposition and so on also need to be considered. Also, another interesting discussion that I have heard relating to brain development in school children is that occupational therapists believe that use of technologically based tools, such as ipad will result in possible changes in motor development and the constant use of eyesight may alter visual development, all on as Jamilah points out a neurocircuitry level.

so, it would follow that a functional examination of occipital cortex size would be the next step in obtaining empirical findings. Size may be a small factor in this, with it increased as a result of increased stimulation in the environment, however, the size may also be attributed to genetic, dietary, maternal lifestyle during gestation etc. Changes in the integrity of networks shared by both groups would give a strong indication of the impact of more complex semantics on visual processing. Similarly, the existence of entirely new patterns of connectivity (as rightly pointed out by Cheryl) due to novel ways of interfacing with visually stimulating technology, would be a very robust indicator of a socioeconomic environment effect.

I am very excited to see the findings from your research Shai.

Larger than what? It is important to know what was being measured and how "larger" was defined and calculated.

I'd look to see if malnutrition plays a role in the differences between impoverished & control. There is a lot of research showing developmental impairment to visual cortex in malnourished animals and humans; however, I'm not sure if the occipital cortex is any more vulnerable than other cortical areas.