One thing that interests me, though the article and study don't touch on it, is that we as humans tend to visualize our number lines on the X axis (e.g. left and right), rather than the Y axis (up and down), Z axis (forward and backward), or W axis (ana and kata).

I know there are some writing systems in which writing is done up/down rather than left/right. I wonder how that influences the spatial visualization of numbers.

I also wonder whether other species might visualize numbers on something other than the X axis.