Fig. 4. Relationship between mean interspike interval (ISI) and coefficient of variation (CV) for regular and irregular primary afferent neurons from dorsal pored (Dp), ventral pored (Vp) and ventral non-pored (Vnp) canals in the Atlantic stingray, Dasyatis sabina. Primary afferents with regular discharge activity (Reg; closed symbols) have lower CV values than irregular units (Irreg; open symbols) for all canal types. ISI values differ between regular and irregular units for Dp and Vp, but not Vnp primary afferents. Further, regular Dp afferents have higher CV and lower ISI values than regular Vnp afferents. Data are plotted as mean ± S.E.M.