Visual adaptation before and after the removal of
bilateral congenital cataracts in adulthood: contrast constancy and border
perception
Contrast constancy and edge perception after the
removal of congenital cataracts as an adult
((I. Fine1, H.S. Smallman1,2,
D.I.A. MacLeod1))
Dept. of Psychology, University of California, San
Diego, CA, 920931;
Pacific Science and Engineering Group, San Diego,
CA 921222.
((I. Fine1,
H.S. Smallman2,
D.I.A. MacLeod1))
Dept. of Psychology, University of California, San Diego, CA, 920931;
Pacific Science and Engineering Group, 6310 Greenwich Drive, San Diego, CA
92122.
Purpose: We have spent the a last
year studying PD, an observer who had severe bilateral congenital
bilateral cataracts from infancy. We have examined
many aspects of PDs visual processing. Here we describe the changes in his
CSFs, and their apparent effect on his supra-threshold contrast matching
and border
perception.
Pre-operatively,
PDs poor optics attenuated high spatial
frequencies. After the first surgery, PD noted new Mach-band-like brightness
perturbations near high contrast borders through his newly operated left eye,
suggesting that he was over-sharpening the improved retinal image. We tracked his
contrast-constancy and his perception of borders post-operatively to see how well he
compensated for his improved optics. We measured his
contrast sensitivity function (CSF) before and after these cataracts were
removed. Before surgery, spatial frequencies above 5 cpd were strongly
attenuated. Postoperatively this attenuation was much less severe. We
have examined many aspects of PDs visual processing - the effects of the
change in his CSF on contrast matching and edge detection will be described
here. Methods: We compared PD and to normals observers
using two tasks. In the contrast matching, task
observers were asked to adjusted the
contrast of sinusoidal test gratings
varying in spatial frequency betweenfrom 0.4 tand
o
12 cpd until their contrast appeared to
matched
that of standard gratings at of 20% contrast with spatial frequencies of
0.47 or 2.36 cpd. In the square wave task, observers were
asked to adjusted the a randomly-modulated square waveform
of a square wave with
aof
fundamental frequency of 1.15 cpd until bright and dark
regions appeared uniform i.e. make a perfect square wave. Results: In the contrast matching task
normal observers showed contrast constancy their contrast settings did
not vary systematically withwere independent of spatial frequency. PD did
not show contrast constancy - with gratings with
spatial frequencies higher than 4 cpd he
strongly underestimated the contrast of gratings higher in frequency than 4 cpd needed
to match the contrast of the low spatial frequency
standards. In the square wave task PD
underestimated the contrast needed in higher spatial frequency components far
more than normal observers (a blurred square wave seemed perfectly square to
him, a real
square wave had Mach bands). Conclusions:
Post-operatively PD over-estimated the contrast of high spatial frequencies in
both tasks, consistent with failing to fully adapt to his post-operative
optics. We modeled PDs performance, and
found we could roughly model that his
performance on both
taskscontrast constancy and square wave tasks were
mutually consistent, and were solely fairly consistent with
the change in his CSF. It appears that PD had developed a
mechanism to sharpen his blurry pre-operative retinal images.
None. Supported by NIH-01711.