Response normalization and blur adaptation: Data and multi-scale model

Abstract

Adapting to blurred or sharpened images alters perceived blur of a focused image (M. A. Webster, M. A. Georgeson, & S. M. Webster, 2002). We asked whether blur adaptation results in (a) renormalization of perceived focus or (b) a repulsion aftereffect. Images were checkerboards or 2-D Gaussian noise, whose amplitude spectra had (log–log) slopes from −2 (strongly blurred) to 0 (strongly sharpened). Observers adjusted the spectral slope of a comparison image to match different test slopes after adaptation to blurred or sharpened images. Results did not show repulsion effects but were consistent with some renormalization. Test blur levels at and near a blurred or sharpened adaptation level were matched by more focused slopes (closer to 1/f) but with little or no change in appearance after adaptation to focused (1/f) images. A model of contrast adaptation and blur coding by multiple-scale spatial filters predicts these blur aftereffects and those of Webster et al. (2002). A key proposal is that observers are pre-adapted to natural spectra, and blurred or sharpened spectra induce changes in the state of adaptation. The model illustrates how norms might be encoded and recalibrated in the visual system even when they are represented only implicitly by the distribution of responses across multiple channels.

Sharpening vision by adapting to flicker

“…Prolonged exposure to images apparently (26) or actually (27)(28)(29) containing lower spatial frequency content can make other images appear sharpened. We do not think this can account for our data.…”

Visual Adaptation

“…This is further complicated by the fact that it is sometimes hard to disentangle properties of channels from properties of the stimulus. For example, whether the channels appear broadly or narrowly tuned depends in part on whether the stimulus itself is best conceived as broad or punctate (Elliott et al, 2011). This difference may seem evident for a single wavelength vs. a light spectrum, but is less certain for many of the complex attributes now probed with adaptation.…”

Norms are Not the Norm: Testing Theories of Sensory Encoding Using Visual Aftereffects

“…Arguably, this could be expected from adaptation to natural scenes (Girshick et al, 2011;Hansen & Essock, 2004). Data pertaining to blur normalisation has been similarly explained, by assuming pre-adaptation to a 1/f spatial frequency distribution (Elliott, Georgeson, & Webster, 2011). It remains to be seen, however, if such explanations are necessary to explain tilt normalisation, as it is unclear if tilt normalisation exists; our data suggests it doesn't.…”

“…After viewing images with distributions that deviate from this, renormalisation can occur, such that the adapted image appears better-focused than it had initially (Elliott et al, 2011). Adaptation to a single spatial frequency, on the other hand, tends to induce a locallyrepulsive aftereffect on single-frequency tests (e.g.…”

“…This allows for a powerful psychophysical method: a spatial comparison task. One can present a standard test stimulus in one location, and find which stimulus value in a second location appears to match it (Elliott et al, 2011;Farell & Pelli, 1999;Jakel & Wichmann, 2006;Kompaniez, Abbey, Boone, & Webster, 2013). At baseline, perceptually-matched stimuli are likely also to be physically matched (for an exception, see Afraz, Pashkam, and Cavanagh (2010)).…”