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Contrast response of temporally sparse dichoptic multifocal visual evoked potentials

Published online by Cambridge University Press:  02 June 2005

TED MADDESS
Affiliation:
Centre for Visual Sciences, Research School of Biological Sciences, Australian National University, Canberra, Australia
ANDREW CHARLES JAMES
Affiliation:
Centre for Visual Sciences, Research School of Biological Sciences, Australian National University, Canberra, Australia
ELIZABETH ANNE BOWMAN
Affiliation:
Centre for Visual Sciences, Research School of Biological Sciences, Australian National University, Canberra, AustraliaCentre for Visual Sciences, John Curtin School of Medical Research, Australian National University, Canberra, Australia

Abstract

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.

Information

Type
Research Article
Copyright
© 2005 Cambridge University Press

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