Do channels shift their tuning towards lower spatial frequencies in the periphery?

Space-variant multichannel spatial vision models include either anchored channels whose units (sensors) share their tuning frequency, or shifting channels whose sensors shift their tuning towards lower frequencies in the periphery. Each type of model embodies a different type of structural organization across eccentricity. Anchored- and shifting-channel models are tested in this paper against empirical data from five types of relevant detection experiment: measurements of the local sine-wave contrast sensitivity function (CSF) at several eccentricities using (a) fixed apertures, (b) apertures scaled with eccentricity or (c) fixed number of cycles, (d) measurements of foveal sensitivity as a function of aperture size, and (e) measurements of the contrast sensitivity gradient across the visual field. Each type of model is shown to predict a different outcome in each type of experiment. A review of empirical research reveals that three of the five experiment types have yielded two distinct sets of results, each of which is consistent with the predictions from one of the types of model, while the two other types of experiment have always yielded similar results which support anchored-channel models. Further scrutiny of the models reveals that the distinction between anchored and shifting channels is more apparent than real, as model predictions are only determined by how sensor gain is assumed to change with eccentricity and tuning frequency. Two alternative sensor gain functions are identified and interpreted in terms of two versions of the cortical magnification theory of spatial vision. Altogether, these two functions account for all extant data on the five types of experiment, suggesting individual differences in the functional organization of the human visual system across eccentricity.