  The constituent quark model based on a hypercentral approach takes into
account three-body force effects and standard two-body potential contributions.
The quark potential contains a hypercentral interaction, to which a hyperfine
term is added. While the hypercentral potential supplies good values for the
centroid energies of the resonance multiplets and a realistic set of quark wave
functions, the hyperfine splittings are sometimes not sufficient to account for
the observed masses.
  In this work we have introduced an improved form of the hyperfine interaction
and an isospin dependent quark potential. The resulting description of the
baryon spectrum is very good, also for the Roper resonance, specially thanks to
the flavour dependent interaction.
