  An experimental study of the in-plane optical conductivity of
(Pb$_{x}$,Bi$_{2-x}$)(La$_{y}$Sr$_{2-y}$)CuO$_{6+\delta}$ (Bi2201) is presented
for a broad doping and temperature range. The in-plane conductivity is analyzed
within a strong coupling formalism. We address the interrelationship between
the optical conductivity ($\sigma(\omega)$), the single particle self energy,
and the electron-boson spectral function. We find that the frequency and
temperature dependence can be well described within this formalism. We present
a universal description of optical, ARPES and tunneling spectra. The full
frequency and temperature dependence of the optical spectra and single particle
self-energy is shown to result from an electron-boson spectral function, which
shows a strong doping dependence and weak temperature dependence.
