PREVENTION OF DEPRIVATION-INDUCED ACUITY LOSS IS DETERMINED BY THE
PROPORTION OF DAILY VISUAL EXPOSURE THAT IS BINOCULAR.
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370.13
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D.E. Mitchell , J. Wynberg , F. Sengpiel , J. Kennie , K.M. Murphy , and P.C. Kind , Psychology Dept., Dalhousie Univ., Halifax, NS, Canada, Biosciences, Cardiff Univ.,
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Cardiff, United Kingdom, Psychology, McMaster Univ., Hamilton, ON, Canada, Biomedical Sciences, Edinburgh Univ., Edinburgh, United Kingdom
Introduction
Question:
On the basis of experiments on kittens that were provided daily with separate periods of normal and
abnormal visual exposure, we have previously shown1 that 2 hr daily periods of concordant binocular
vision (BE) prevent the consequences of selected visual deprivation during development. For 4 weeks
beginning at 4 weeks of age, the total visual experience each day of kittens was restricted to 7 hours
split unevenly between periods of monocular (ME) and binocular (BE) exposure [1]. For the former
exposure, the kittens wore an opaque mask [3] that covered one eye, while for the latter the mask was
removed to allow binocular exposure. The kittens were placed with their mother in a darkroom for the
remaining 17 hours each day. As little as 2 hr periods of BE outweigh or protect against much longer
daily periods (5 hr) of ME to allow the development of normal visual acuities in both eyes [2]. We
now ask whether it is the proportion of the total visual exposure that is BE (2/7 or approx 30%), or the
absolute number of such hours (ie. 2 hrs) that is critical for this beneficial outcome. To address this
issue, we reduced the total visual exposure by half, from 7 to 3.5 hr. If the proportion of daily visual
exposure that is binocular is the crucial factor, then only 1 hour of BE daily will be sufficient to
achieve normal visual acuity in each eye.
Is the critical factor the absolute number of hours of BV each day (i.e. 2 hours), or the
proportion of the 7 hours of daily visual exposure that is binocular (i.e. 2/7 or
approximately 30%)?
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2
Deprived Eye Visual Acuity (cycles/deg.)
7 hours
L
R
A
L
R
B
Two hours of normal vision each day permits
development of normal visual acuity in the deprived eye.
Symbols shaded on the left or right depict respectively,
kittens for which the period of ME was first or second.
The square symbol and bar displays the mean and
standard deviation of the acuities measured in the nondeprived eye of all animals.
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Front
Back
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Opaque Mask (OM)
1 hr
1.5 hr
2.5 hr
BE
BE
ME
ME
BE
7
Acuity (cycles/deg.)
6
5
NDE
4
DE
3
2
B
0
C938 C939 C940 C965 C968 C969 C990
C936 C937 C967 C966
C987
Same Proportion of BE
(1 hr BE)
Same Amount of BE
(2 hr BE)
No BE
L
R
Conclusions
Results
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The Visual Experience of 12 kittens during the 4 weeks of selected visual exposure, the type of
occlusion (OM: opaque mask versus TO: translucent occluder) and the effects on the acuities of the
two eyes.
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1
0
Cat
Blind
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
7
Hours of Binocular Experience Per Day
Diagrammatic
representation of the
jumping stand
Mask with
translucent occluder
(TO)
ME
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If the proportion of daily visual exposure
that is binocular is the critical factor, then
1 hour of BV daily will be sufficient to
achieve normal visual acuity in each eye.
ME
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L
R
2. Measurement of Visual Acuity
Measurement of the visual acuity of the non-deprived eye for square-wave gratings was made by use
of a jumping stand [4] immediately prior to termination of the period of mixed visual exposure while
the acuity of the deprived eye was assessed the next day immediately after the kittens were taken from
the darkroom. Training was begun on the jumping stand during the periods of BE at 5 weeks of age.
R
If the absolute number of hours is crucial,
then it will still require 2 hours of BV
each day to achieve normal visual acuity
in each eye.
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1. Rearing
Twelve kittens (3 litters) were reared with their mothers from 4 wks to 8 wks of age in a darkroom.
Each litter was removed for 3.5 hr each day to a normally illuminated environment. A mask was used
to occlude one eye for the required period of ME each day. Half the kittens received 1 hr BE (and 2.5
hr ME) each day, representing the same proportion of BE that maintained normal development of
visual acuity in the kittens of the earlier study. The remaining kittens received 2 hr BE (and 1.5 hr
ME), the same absolute BE exposure as in the previous study.
S1
The question can be answered in part by reducing the total visual exposure by a factor of 2
from 7 to 3.5 hours.
2 hr
Methods
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BE
C987
C938
C939
C940
C965
C968
C969
C990
C936
C937
C966
C967
Hours of Visual
Exposure
BE
ME
3.5
1
2.5
1
2.5
1
2.5
1
2.5
1
2.5
1
2.5
1
2.5
2
1.5
2
1.5
2
1.5
2
1.5
Mask
Order
OM
TO
OM
OM
TO
OM
OM
OM
OM
OM
OM
OM
ME
BE-ME
BE-ME
BE-ME
BE-ME
ME-BE
ME-BE
ME-BE
BE-ME
BE-ME
ME-BE
ME-BE
Deprived Eye Acuity Non-deprived Eye Acuity
(cycles/degree)
(cycles/degree)
Blind
6.19
6.19
6.59
6.19
6.59
6.19
6.59
6.19
6.19
6.19
6.19
6.19
6.19
6.19
6.19
6.59
6.59
6.59
6.59
5.94
5.94
6.19
6.19
As expected, the kitten that received no BE (C987) appeared blind (B) in the non-exposed
(deprived) eye.
All 7 kittens that received only 1 hour of BE achieved a visual acuity with the deprived eye
equal to or closely similar to that of the fellow eye and to those of normal kittens of the same age.
The 4 kittens that received 2 hrs BE also achieved normal visual acuities with their deprived eye.
It appears that when the total daily visual exposure is 3.5 hrs or more, then it is the proportion of
this exposure that is binocular (approx. 30%) that allows for the development of normal visual
acuity in both eyes.
The order of exposure (ME first or second) did not appear to influence the outcome.
The acuities of the deprived eye of all kittens were either identical or very close to that of the
fellow non-deprived eye and to the acuities of normal animals of equivalent age.
Because one hour of daily normal (i.e. binocular) visual exposure could outweigh or protect
against 2.5 hours of daily monocular exposure, it appears that for daily visual exposures of 3.5
hours or more, that it is the proportion rather than the amount of binocular daily visual exposure
(i.e. approx. 30%) that permits the development of normal visual acuities in both eyes.
This conclusion is compatible with a finding of Watanabe et al2 who found that 4 hours of daily
BE (equivalent to 33% of the 12 hours of daily visual exposure) protected against the behavioural
and physiological effects of monocular deprivation in monkeys.
As with the earlier experiments1, the results were no different in animals that received their
period of ME second as opposed to first. Thus, it appears that it is the amount and not the timing of
binocular experience that dictates the outcome.
A further implication of our finding is that the molecular events that underlie the protective
effects of daily BE require as little as 1 hour of such exposure.
References
1. Mitchell, D.E., Kind, P.C., Sengpiel, F, and Murphy,
K.M. Brief daily periods of binocular vision prevent
deprivation-induced acuity loss. Current Biology 13:
1704-1708, 2003.
2. Watanabe I, Zhang B, Zheng J, Wensveen JM,
Harwerth RS, Smith EL, Chino YM (2004) Effects of
brief unrestricted vision during early monocular form
deprivation in macaque monkeys. Soc Neurosci .
Program No. 939.6. 2004.
Contact Information:
Dr. Donald E. Mitchell
Psychology Department
Dalhousie University
Halifax, Nova Scotia
Canada
B3H 4J1
(902) 494-6419
E-Mail: D.E.Mitchell@Dal.ca
World Wide Web URL of this poster:
http://myweb.dal.ca/mitchell