locus                  package:emu                  R Documentation

_C_a_l_c_u_l_a_t_e _l_o_c_u_s _e_q_u_a_t_i_o_n_s _f_o_r _t_w_o-_d_i_m_e_n_s_i_o_n_a_l _d_a_t_a

_D_e_s_c_r_i_p_t_i_o_n:

     The function plots a locus equation and returns associated 
     statistical information.

_U_s_a_g_e:

     locus (target, onset, labels.vow = NULL, yxline = TRUE, plotgraph = TRUE,  axes = TRUE, ...) 

_A_r_g_u_m_e_n_t_s:

  target: a numerical vector typically of F2 values at the vowel target

   onset: a numerical vector typically of the same length as target of 
          F2 values at the vowel onset

labels.vow: an optionally character vector for plotting labels at the
          points (target, onset) of the same length as target

  yxline: optionally plot the line target = onset.  Defaults to True.

plotgraph: a logical vector for specifying whether the data should be
          plotted. Defaults to True.

    axes: A logical vector indicating whether the axes should be
          plotted

     ...: graphical options par

_D_e_t_a_i_l_s:

     A locus equation is a straight line regression fitted with lm() in
     which the F2- values typically at the vowel onset are regressed on
     those of the target. The slope can be used to give an indication
     of target-on-onset coarticulatory influences. 

     The best estimate  of the locus frequency is where the locus
     equation bisects the line target = onset.

_V_a_l_u_e:

     A list containing regression diagnostics of the function lm() that
     can be accessed with summary() and the estimated locus frequency
     in $locus. A plot of values in the onset x target plane with
     superimposed locus equation and line onset=target.

_A_u_t_h_o_r(_s):

     Jonathan Harrington

_E_x_a_m_p_l_e_s:

      # calculate an F2-locus equation for initial [d] 
     # preceding lax vowels produced by female speaker "68".
     # the onset is taken at the vowel onset; the
     # vowel target is taken at the vowel's temporal midpoint.

     # identify initial "d" of speaker "68"
     temp <- vowlax.left == "d" & vowlax.spkr == "68"
     # get the F2 value at the vowel's temporal midpoint
     targ <- dcut(vowlax.fdat[temp,2], .5, prop=TRUE)
     # F2 value at the vowel's acoustic onset.
     on <- dcut(vowlax.fdat[temp,2], 0, prop=TRUE)

     # locus equation plot
     result <- locus(targ, on, vowlax.l[temp])
     # statistical diagnostics of the regression line (locus equation)
     summary(result)
     # intercept and slope
     result$coeff
     # best estimate of the locus frequency, i.e. the
     # point of bisection of on = TRUEarg with the regression line
     result$locus

