Figure 4.

When the angle θ between the x-axis and z-axis is not the same as in the Cartesian coordinate system, the spatial relationships among these axes and visual perception are also different. (A) The included angle <a onClick="popup('http://www.biomedcentral.com/1471-2202/15/50/mathml/M20','MathML',630,470);return false;" target="_blank" href="http://www.biomedcentral.com/1471-2202/15/50/mathml/M20">View MathML</a>, angle θ from 120° (a) to 90° (e). In case (e), there is no stereoscopic perception. (B) The included angle θ from 90° a to 120° e. In case a, there is no stereoscopic perception. (C) The included angle θ from 90° e to 120° a, obtained by rotating (A) 90° in the vertical direction and turned 30° in the horizontal direction. In case (e), there is no three-dimensional perception.

Songnian et al. BMC Neuroscience 2014 15:50   doi:10.1186/1471-2202-15-50
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