Kinematics maps and velocity dispersion Fourier analysis histograms for the toy models with a weak velocity gradient rotation curve (v₀ = 200 km s⁻¹, r_s = 100″ and γ = 1) without any perturbation (top), and with a spiral velocity perturbation towards either radial (middle) or azimuthal (bottom) components. We show, from left to right the density map, the velocity field and the BS corrected dispersion maps in the isotropic and anisotropic cases, obtained with an inclination of 60° and with ϕ_sp = 135°. We show from left to right amplitude histograms of orders k = 2 and k = 4 and normalised phase angle histograms of these orders, obtained from the FFT analysis of toy models dispersion maps. Blue and green histograms correspond to isotropic and anisotropic cases respectively.