System analysis of Phycomyces light-growth response with Gaussian white noise and sum-of-sinusoids test stimuli

Edward Lipson, Promod Pratap

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The sporangiophore (fruiting body) of the fungus Phycomyces modulates its elongation rate in response to changes in blue light intensity. This light-growth response of wild-type and behavioral mutant strains has been studied extensively by two methods of nonlinear system identification employing Gaussian white noise and sum-of-sinusoids test stimuli. Both methods are in the framework of the Wiener theory of nonlinear systems. The light-growth response is well described by the first-order Wiener G-functional; addition of the second-order functional improves the precision. The Wiener kernel of first-order resembles the light-growth response to a nonsaturating pulse stimulus. The second-order kernel indicates the nonlinear property of rectification. The kernels have been interpreted by system analysis methods in the frequency domain. A nonlinear dynamic model of the light-growth response has been developed from the kernels obtained by both methods. The model includes a nonlinear dynamic subsystem, including a squarer, followed by a linear dynamic subsystem (which, by itself, accounts for the first-order kernel). This parametric model has been used to evaluate light-growth response kernels under various conditions (viz. wavelength, temperature, and genetic strain). The kernels of single and double mutants have been analyzed jointly with a nonparametric model to reveal interactions among the products of eight genes that influence the light-growth response. The extent of interactions found suggests that these gene products function together in a molecular complex.

Original languageEnglish (US)
Pages (from-to)95-109
Number of pages15
JournalAnnals of Biomedical Engineering
Issue number1
StatePublished - Jan 1988


  • Gaussian white noise
  • Photobiology
  • Physiological system analysis
  • Sum-of-sinusoids
  • System identification

ASJC Scopus subject areas

  • Biomedical Engineering


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