Spatial-frequency properties of letter identification in amblyopia

Spatial-frequency properties of letter identification in amblyopia Amblyopia is characterized by a deficit in identifying small letters (acuity deficit) in the absence of identifiable ocular pathology. One explanation for this deficit is that the amblyopic visual system lacks appropriate channels tuned to high spatial frequencies for identifying small letters. The purpose of this study was to examine the spatial-frequency properties of letter identification in the amblyopic visual system. To do so, we measured contrast thresholds for identifying letters that were band-pass filtered to different bands of spatial frequencies, for letter sizes ranging from 2× to 19.2× larger than acuity letters. Letters were digitally filtered using a set of band-pass filters, with peak object spatial frequencies ranging from 0.88 to 10 c/letter. The bandwidth of the filters was 1 octave. For any given letter size, contrast sensitivity for identifying letters exhibits a spatial-tuning function. The shape of these tuning functions was found to be similar between amblyopic and non-amblyopic eyes, and across all letter sizes. The peak of these functions shifted progressively toward lower object spatial frequency when the letter size became smaller. When compared with the non-amblyopic eyes, the amblyopic eyes have a limited range of tuning functions sensitive to letters. However, when scaled with respect to acuity, the relationship between the peak frequency of the tuning functions and letter size becomes essentially identical in the amblyopic and non-amblyopic eyes. An ideal-observer analysis that takes into account spectral information about letter identity and the contrast-sensitivity function of the observer, but does not invoke narrow-band channels, also shows that the properties of the tuning functions for letter identification are similar between the amblyopic and non-amblyopic eyes. We conclude that the deficit in identifying small letters in amblyopes is not attributable to differences in the shape or selection of “channels”, when compared with the normal visual system. Rather, it is a consequence of the difference in the resolution limit between the amblyopic and the non-amblyopic eyes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Vision Research Elsevier

Spatial-frequency properties of letter identification in amblyopia

Loading next page...
 
/lp/elsevier/spatial-frequency-properties-of-letter-identification-in-amblyopia-6gqdJlzYGk
Publisher
Elsevier
Copyright
Copyright © 2002 Elsevier Science Ltd
ISSN
0042-6989
eISSN
1878-5646
DOI
10.1016/S0042-6989(02)00065-2
Publisher site
See Article on Publisher Site

Abstract

Amblyopia is characterized by a deficit in identifying small letters (acuity deficit) in the absence of identifiable ocular pathology. One explanation for this deficit is that the amblyopic visual system lacks appropriate channels tuned to high spatial frequencies for identifying small letters. The purpose of this study was to examine the spatial-frequency properties of letter identification in the amblyopic visual system. To do so, we measured contrast thresholds for identifying letters that were band-pass filtered to different bands of spatial frequencies, for letter sizes ranging from 2× to 19.2× larger than acuity letters. Letters were digitally filtered using a set of band-pass filters, with peak object spatial frequencies ranging from 0.88 to 10 c/letter. The bandwidth of the filters was 1 octave. For any given letter size, contrast sensitivity for identifying letters exhibits a spatial-tuning function. The shape of these tuning functions was found to be similar between amblyopic and non-amblyopic eyes, and across all letter sizes. The peak of these functions shifted progressively toward lower object spatial frequency when the letter size became smaller. When compared with the non-amblyopic eyes, the amblyopic eyes have a limited range of tuning functions sensitive to letters. However, when scaled with respect to acuity, the relationship between the peak frequency of the tuning functions and letter size becomes essentially identical in the amblyopic and non-amblyopic eyes. An ideal-observer analysis that takes into account spectral information about letter identity and the contrast-sensitivity function of the observer, but does not invoke narrow-band channels, also shows that the properties of the tuning functions for letter identification are similar between the amblyopic and non-amblyopic eyes. We conclude that the deficit in identifying small letters in amblyopes is not attributable to differences in the shape or selection of “channels”, when compared with the normal visual system. Rather, it is a consequence of the difference in the resolution limit between the amblyopic and the non-amblyopic eyes.

Journal

Vision ResearchElsevier

Published: Jun 1, 2002

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off