title: Time-frequency analysis of electronystagmogram signals in patients with congenital nystagmus.
abstract: OBJECTIVE
  To evaluate the usefulness of the short-time Fourier transform (STFT) in the analysis of temporal congenital nystagmus characteristics.
  
  
  METHODS
  We carried out an observational case series in patients with congenital nystagmus. An electronystagmogram (ENG) recording was performed for 300 s in 13 consecutive subjects with congenital nystagmus (age: 7-68 years). Digitized ENG signals (12 bits, 100 Hz) were divided into 2-s segments with a Hanning window, and a Fourier transform was carried out for each segment. The power spectrum obtained for each segment was graphically reconstructed as a function of time. The results were compared among the patients.
  
  
  RESULTS
  Clear periodicity in the time-frequency distribution was observed in 3 of the 13 patients (23%). One of the three patients was diagnosed with periodic alternating nystagmus, but the other two patients showed periodicity without alternation of beat direction. No significant difference was observed in clinical characteristics, except for sex, between patients who showed periodicity and those who did not.
  
  
  CONCLUSIONS
  Some patients with congenital nystagmus showed clear periodicity in the nystagmus waveform without alternation of beat direction. The STFT is a useful tool to evaluate the temporal characteristics of congenital nystagmus in clinics.
authors.affiliation: Department of Ophthalmology, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan.
authors.forename: Mitsuto
authors.initials: M
authors.lastname: Hosokawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hasebe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohtsuki
authors.forename: Yozo
authors.initials: Y
authors.lastname: Tsuchida
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D004584:Electronystagmography; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D020417:Nystagmus, Congenital / Q000503:physiopathology*; D010507:Periodicity; D013997:Time Factors