Blur adaptation explained by a norm-based model of contrast adaptation

Mark A. Georgeson, Sarah L. Elliott, Michael A. Webster

Research output: Unpublished contribution to conferenceUnpublished Conference Paperpeer-review

Abstract

Adapting to blurred images makes in-focus images look too sharp, and vice-versa (Webster et al, 2002 Nature Neuroscience 5 839 - 840). We asked how such blur adaptation is related to contrast adaptation. Georgeson (1985 Spatial Vision 1 103 - 112) found that grating contrast adaptation followed a subtractive rule: perceived (matched) contrast of a grating was fairly well predicted by subtracting some fraction k(~0.3) of the adapting contrast from the test contrast. Here we apply that rule to the responses of a set of spatial filters at different scales and orientations. Blur is encoded by the pattern of filter response magnitudes over scale. We tested two versions - the 'norm model' and 'fatigue model' - against blur-matching data obtained after adaptation to sharpened, in-focus or blurred images. In the fatigue model, filter responses are simply reduced by exposure to the adapter. In the norm model, (a) the visual system is pre-adapted to a focused world and (b) discrepancy between observed and expected responses to the experimental adapter leads to additional reduction (or enhancement) of filter responses during experimental adaptation. The two models are closely related, but only the norm model gave a satisfactory account of results across the four experiments analysed, with one free parameter k. This model implies that the visual system is pre-adapted to focused images, that adapting to in-focus or blank images produces no change in adaptation, and that adapting to sharpened or blurred images changes the state of adaptation, leading to changes in perceived blur or sharpness.
Original languageEnglish
Publication statusUnpublished - 2009
EventApplied Vision Association Annual 2009 Meeting - Birmingham , United Kingdom
Duration: 31 Mar 2009 → …

Other

OtherApplied Vision Association Annual 2009 Meeting
CountryUnited Kingdom
CityBirmingham
Period31/03/09 → …

Bibliographical note

Abstract published in Applied Vision Association Annual 2009 Meeting, Perception, 38(4), p. 623. ISSN: 0001-4966.

Keywords

  • blurred images
  • in-focus images
  • blur adaptation
  • contrast adaptation
  • grating contrast adaptation
  • sharpness

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