Dr Ron Gray, from Oxford University, who led the research added that although the differences appeared small, they may well be significant and that lower IQ hadbeen shown to be associated with being socially disadvantaged, having poorer health and even dying younger.
She said it was estimated that 30% of the EU egg-laying flock would still be in conventional cages by 2012, and that she hadbeen pressing the EU Commission to ensure local producers were not disadvantaged.