Detection in power-law noise: spectrum exponents and CD diagram slopes

摘要

Normal mammographic image backgrounds have approximately isotropic power spectra of the form, P(f) = K/f~β, where f is radial frequency. The values of the exponent, β, range from 1.5 to 3.5 with an average of about 2.8. The ideal observer model predicts that, for signals with certain properties, the log-log contrast-detail (CD) diagram slope, m, is given by: m = 0.5(β-2). Previously, we reported results for detection of a model mass (designer nodule) in filtered noise with an exponent of 3. The model and human observer CD slopes were 0.5 and 0.45 respectively. Here, we report preliminary results for human and model observer 2AFC detection of a simple signal in filtered noise with exponents from 1.5 to 3.5. Our results are in good agreement with the prediction of the above equation. We will also describe results of 2AFC detection experiments done using "twin" noise backgrounds with identical noise realizations in the two backgrounds. We could not replicate the results of Johnson et al. For '1/f~3' noise, they found a CD slope of -0.59 while we found +0.37.