Amblyopia masks the scale invariance of normal central vision.
In normal vision, detecting a kink (a change in orientation) in a line is scale invariant: it depends solely on the length/width ratio of the line (D. Whitaker, D. M. Levi, & G. J. Kennedy, 2008). Here we measure detection of a change in the orientation of lines of different length and blur and show that strabismic amblyopia is qualitatively different from normal foveal vision, in that: 1) stimulus blur has little effect on performance in the amblyopic eye, and 2) integration of orientation information follows a different rule. In normal foveal vision, performance improves in proportion to the square root of the ratio of line length to blur (L:B). In strabismic amblyopia improvement is proportional to line length. Our results are consistent with a substantial degree of internal neural blur in first-order cortical filters. This internal blur results in a loss of scale invariance in the amblyopic visual system. Peripheral vision also shows much less effect of stimulus blur and a failure of scale invariance, similar to the central vision of strabismic amblyopes. Our results suggest that both peripheral vision and strabismic amblyopia share a common bottleneck in having a truncated range of spatial mechanisms--a range that becomes more restricted with increasing eccentricity and depth of amblyopia.
Levi
Dennis M
DM
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA, USA. dlevi@berkeley.edu
Whitaker
David
D
Provost
Allison
A
D000550:Amblyopia / Q000150:complications* / Q000503:physiopathology / Q000523:psychology*; D004056:Differential Threshold; D004192:Discrimination, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010470:Perceptual Masking; D013028:Space Perception; D013285:Strabismus / Q000150:complications*; D014794:Visual Fields; D014796:Visual Perception; D055815:Young Adult