Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_spike_rate_orituning”.

  FT_SPIKE_RATE_ORITUNING computes a model of the firing rate as a function
  of orientation or direction.
  Use as
    [stat] = ft_spike_rate_tuning(cfg, rate1, rate2, ... rateN)
  The inputs RATE should be the output from FT_SPIKE_RATE. 
    cfg.stimuli  = should be an 1 x nConditions array of orientations or
                   directions in radians
                   varargin{i} corresponds to cfg.stimuli(i)
    cfg.method   = model to apply, implemented are 'orientation' and 'direction'
    stat.ang       = mean angle of orientation / direction (1 x nUnits)
    stat.osi       = orientation selectivity index (Womelsdorf et al., 2012,
                     PNAS), that is resultant length.
                     if cfg.method = 'orientation', then orientations are
                     first projected on the unit circle.
    stat.di        = direction index, 1 - min/max response