The average shape of micropulses in two pulsars is highly symmetric, unlike the subpulse emission which is skewed in the same sense as the average profiles. These conclusions stem from a third-order correlation analysis of the emission from PSR 0950+08 and PSR 2016+28. The symmetric micropulses may be produced either by temporal modulation or angular beaming of the radiation. If due to temporal modulation, this average symmetry implies a distribution of time-scales in the emission process: the difference between the rise time-scale (τr) and the decay time-scale (τd) must be small compared to δτr and/or δτd. Subpulses in PSR 0950+08 are narrower than and have the same sense of asymmetry as the average profile. In PSR 2016+28 the two subpulses typically present in a pulse are both tapered toward the outside edge of the pulse. In both pulsars, the skewness of the subpulses contributes significantly to the skewness of the average profile; a symmetrical distribution of these subpulses within the pulse window could then give rise to an asymmetrical profile.