title: Effect of varying CRT refresh rate on the measurement of temporal summation.
abstract: OBJECTIVE
  To quantify the effect of cathode-tube-ray (CRT) monitor refresh rate on the measurement of the upper limit of complete temporal summation (critical duration) in the peripheral visual field of healthy observers.
  
  
  METHODS
  Contrast thresholds were measured for seven achromatic spot stimuli (diameter 0.48°) of varying duration (nominal values: 10-200 ms) at an eccentricity of 8.8° along the 45°, 135°, 225° and 315° meridians of the visual field in three healthy, psychophysically experienced observers. Stimuli were presented on a CRT display with a refresh rate of 60 and 160 Hz. Contrast thresholds were expressed as contrast energy with stimulus durations being estimated using (1) the sum-of-frames (SOF) method and (2) Bridgeman's method incorporating measurements of phosphor persistence. Estimates of the critical duration were produced using iterative two-phase regression analysis.
  
  
  RESULTS
  With stimulus duration expressed as SOF equivalent the critical duration was, on average, 10.6 ms longer with a refresh rate of 60 Hz (mean 45.7 ms, S.D. 10.1 ms) relative to 160 Hz (35.1 ms, S.D. 7.6 ms). When the Bridgeman method was used, minimal differences (1.8 ms) in critical duration values between the two refresh rates (60 Hz: 33.0 ms, S.D. 9.4 ms; 160 Hz: 31.2 ms, S.D. 7.0 ms) were observed. Identical trends were observed in all three subjects.
  
  
  CONCLUSIONS
  Psychophysical measurements of temporal summation are independent of variations in CRT refresh rate when the Bridgeman method, incorporating measured values of phosphor persistence, is used to estimate stimulus duration. This has significant implications for the specification of stimulus duration in psychophysical studies of vision employing conventional display monitors.
authors: National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.|Vision Science Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, UK.
authors: Pádraig J
authors: PJ
authors: Mulholland
authors: Vision Science Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, UK.
authors: Margarita B
authors: MB
authors: Zlatkova
authors: School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
authors: Tony
authors: T
authors: Redmond
authors: National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.
authors: David F
authors: DF
authors: Garway-Heath
authors: National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.|Vision Science Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, UK.
authors: Roger S
authors: RS
authors: Anderson
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D011601:Psychophysics / Q000379:methods*; D012684:Sensory Thresholds / Q000502:physiology*; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*
keywords: cathode-ray-tube; critical duration; refresh rate; stimulus duration; temporal summation