Lookup NU author(s): Dr Ignacio Serrano-Pedraza,
Dr Mario Siervo,
Professor Andrew Derrington
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In the study of the spatial characteristics of the visual channels, the power-spectrum model of visual masking is one of the most widely used. When the task is to detect a signal masked by visual noise, this classical model assumes that the signal and the noise are previously processed by a bank of linear channels and that the power of the signal at threshold is proportional to the power of the noise passing through the visual channel that mediates detection. The model also assumes that this visual channel will have the highest ratio of signal power to noise power at its output. According to this, there are masking conditions where the highest signal to noise ratio occurs in a channel centred in a spatial frequency different from the spatial frequency of the signal (off-frequency looking). Under these conditions the channel mediating detection could vary with the type of noise used in the masking experiment and this could affect the estimation of the shape and the bandwidth of the visual channels. It is generally believed that notched noise, white noise and double band-pass noise prevent off-frequency looking, and high-pass, low-pass and band-pass noises can promote it independently of the channel’s shape. In this study, by means of a procedure that finds the channel that maximizes the signal-to-noise ratio at its output, we performed numerical simulations using the power-spectrum model to study the characteristics of masking caused by six types of 1-D noise (white, high-pass, low-pass, band-pass, notched, and double band-pass) for two types of channel’s shape (symmetric and asymmetric). Our simulations confirm that (1) high-pass, low-pass, and band-pass noises do not prevent the off-frequency looking, (2) white noise satisfactorily prevents the off-frequency looking independently of the shape and bandwidth of visual channel, and interestingly we proved for the first time that (3) notched and double band-pass noises prevent the off-frequency looking only when the noise cutoffs around the spatial frequency of the signal matches the shape of the visual channel (symmetric and asymmetric) involved in the detection. In order to test the explanatory power of the model with empirical data, we performed six visual masking experiments. We show that this model, with only two free parameters, fits the empirical masking data with high precision. Finally, we provide particular equations of the power-spectrum model for six masking noises used in the simulations and in the experiments.
Author(s): Serrano-Pedraza I, Sierra-Vázquez V, Derrington AM
Publication type: Article
Publication status: Published
Journal: Journal of the Optical Society of America A: Optics, Image Science, and Vision
Print publication date: 14/05/2013
ISSN (print): 1084-7529
ISSN (electronic): 1520-8532
Publisher: Optical Society of America
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