Temporally sparse stimuli have been found to produce larger multifocal
visual evoked potentials than rapid contrast-reversal stimuli. We compared
the contrast-response functions of conventional contrast-reversing (CR)
stimuli and three grades of temporally sparse stimuli, examining both the
changes in response amplitude and signal-to-noise ratio (SNR). All stimuli
were presented dichoptically to normal adult human subjects. One stimulus
variant, the slowest pattern pulse, had interleaved monocular and
binocular stimuli. Response amplitudes and SNRs were similar for all
stimuli at contrast 0.4 but grew faster with increasing contrast for the
sparser stimuli. The best sparse stimulus provided an SNR improvement that
corresponded to a recording time improvement of 2.6 times relative to that
required for contrast reversing stimuli. Multiple regression of
log-transformed response metrics characterized the contrast-response
functions by fitting power-law relationships. The exponents for the two
sparsest stimuli were significantly larger (P < 0.001) than
for the CR stimuli, as were the mean response amplitudes and
signal-to-noise ratios for these stimuli. The contrast-dependent response
enhancement is discussed with respect to the possible influences of rapid
retinal contrast gain control, or intracortical and cortico-geniculate
feedback.