Document Detail

Noise frame duration, masking potency and whiteness of temporal noise.
MedLine Citation:
PMID:  12202539     Owner:  NLM     Status:  MEDLINE    
PURPOSE: Because of the limited contrast range, increasing the duration of the noise frame is often the only option for increasing the masking potency of external, white temporal noise. This, however, reduces the high-frequency cutoff beyond which noise is no longer white. This study was conducted to determine the longest noise frame duration that produces the strongest masking effect and still mimics white noise on the detection of sinusoidal flicker. METHODS: Contrast energy thresholds (E(th)) were measured for flicker at 1.25 to 20 Hz in strong, purely temporal (spatially uniform), additive, external noise. The masking power of white external noise, characterized by its spectral density at zero frequency N0, increases with the duration of the noise frame. RESULTS: For short noise frame durations, E(th) increased in direct proportion to N0, keeping the nominal signal-to-noise ratio [SNR = (E(th)/N0)(0.5)] constant at threshold. The masking effect thus increased with the duration of the noise frame and the noise mimicked white noise. When noise frame duration and N0 increased further, the nominal SNR at threshold started to decrease, indicating that noise no longer mimicked white noise. The minimum number of noise frames per flicker cycle needed to mimic white noise decreased with increasing flicker frequency from 8.3 at 1.25 Hz to 1.6 at 20 Hz. CONCLUSIONS: The critical high-frequency cutoff of detection-limiting temporal noise in terms of noise frames per signal cycle depends on the temporal frequency of the signal. This is opposite to the situation in the spatial domain and must be taken into consideration when temporal signals are masked with temporal noise.
Heljä Kukkonen; Jyrki Rovamo; Kristian Donner; Marja Tammikallio; Antti Raninen
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Investigative ophthalmology & visual science     Volume:  43     ISSN:  0146-0404     ISO Abbreviation:  Invest. Ophthalmol. Vis. Sci.     Publication Date:  2002 Sep 
Date Detail:
Created Date:  2002-08-30     Completed Date:  2002-09-12     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7703701     Medline TA:  Invest Ophthalmol Vis Sci     Country:  United States    
Other Details:
Languages:  eng     Pagination:  3131-5     Citation Subset:  IM    
Department of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom.
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MeSH Terms
Contrast Sensitivity / physiology
Middle Aged
Perceptual Masking / physiology*
Pitch Perception / physiology*
Sensory Thresholds
Visual Perception / physiology*

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