The checkerboard-onset evoked potential does not obtain its adult wave
form until late puberty. The changing waveform results from the develo
pment of the underlying sources originating in distinct areas of the v
isual cortex. Since the waveform of checkerboard-onset evoked potentia
l also varies with check size, we studied the dependency of the activi
ty of these sources on check size. A dipole source localization proced
ure yielded the position and orientation of the equivalent dipoles and
the constituent components of the pattern-onset evoked potential, eac
h corresponding to one of these dipoles. For every check size used, th
e checkerboard-onset evoked potential could be described by a summatio
n of the relative amplitudes of these components. Since the relative a
mplitude versus check size curves showed a different behavior for each
source, they provided evidence of functionally distinct cortical gene
rators. The strength of the striate source was especially sensitive to
the fine structure of a pattern, whereas the extrastriate sources con
tributed mainly for coarse pattern elements.