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| Research article summary (published 30 Aug 2002): |
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Noise frame duration, masking potency and whiteness of temporal noise.
Full Abstract
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.
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Author information
Author/s: Kukkonen, Heljä (H); Rovamo, Jyrki (J); Donner, Kristian (K); Tammikallio, Marja (M); Raninen, Antti (A);
Affiliation: Department of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom.
Journal and publication information
Publication Type: Journal Article; Research Support, Non-U.S. Gov't
Journal: Investigative ophthalmology & visual science (Invest Ophthalmol Vis Sci), published in United States. (Language: eng)
Reference: 2002-Sep; vol 43 (issue 9) : pp 3131-5
Dates: Created 2002/08/30; Completed 2002/09/12; Revised 2006/11/15;
PMID: 12202539, status: MEDLINE (last retrieval date: 11/6/2008)
Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.
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