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- Jerome Cohen, Xue Han, Anca
Matei, Vara Parameswaran
- Department of Psychology, University of Windsor
- Myron Hlynka
- Department of Mathematics and Statistics, University of Windsor
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- DMTS, DNMTS, radial maze, food cache recovery errors not always due =
to
loss in working memory (Thorpe, Jacova, Wilkie, 2004; Wilkie, Willso=
n,
Carr, 1999)
- Overestimation (Cole & Chappell-Stephenson, 2004) or underestima=
tion
(Cohen et al. 2004) of spatial location working memory in radial maze
task
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- Open radial maze tasks confounded with direction cues
- Rats may retain how far away arms are from a given direction sampled
rather than specific arm locations.
- Object recognition tasks: DMTS, DNMTS, novel object recognition (see
Mumby, 2001)
- Assess retention interval for one or two objects
- Non-spatial DMTS, DNMTS versions difficult to acquire.
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- Object recognition task should be easy to acquire
- Working memory should be biologically more relevant to the animal th=
an
search response algorithms
- Reward new object recovery so as to prevent premature search termina=
tion
- Large pool of objects to prevent proactive interference from object
repetition over successive trials
- Assess individual animal’s working memory capacity
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- Subjects: Six Long-Evans male hooded rats
- Apparatus: Large enclosed square foraging area with 25 (5 x 5) cover=
ed
food wells
- Only food wells covered with objects baited with sunflower seeds
- Pool of 60 objects
- Trials partitioned into study and test segments
- Study segment: n object-covered wells, each baited with one seed
- Test segment: one or more ‘new’ objects replace
‘old’ objects - baited with 6 seeds
- I-min inter-segment-interval
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- Phase 1 trial: One new object in test segment replaces one of the th=
ree old
objects from previous study segment.
- Object locations randomized over trials but not within a trial
- Phase 2 trial: Two new objects in test segment replace two of the si=
x old
objects from previous study segment
- Phase 3 trial: Three new objects in test segment replaces three of n=
ine old
objects from previous study segment.
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9
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- Number of choices to find all “jackpot” objects
- Observed distribution of cumulative proportion of trials rat finds a=
ll
jackpots in each phase.
- Compare observed distributions with theoretical cumulative probabili=
ty
distributions for finding all jackpots based on no memory (chance) to
perfect working memory of all ‘old’ objects from the stu=
dy
segment (K-S tests)
- Estimate of recognized old objects based on 95% confidence interval
around the observed distribution.
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- Phase 1: No rat shows above chance performance in finding one jackpot
out of three objects.
- Phase 2: All rats show above chance performance in finding two jackp=
ots
out of six objects.
- Phase 3: Five rats show above chance performance in finding three
jackpots out of nine objects.
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- Phase 2: Six objects / Phase 3: Nine objects
- Rat 2B between 1 and =
4 / 0
and 4
- Rat 2D between 2 and =
4 / 6
and 8
- Rat 3A between 0 and =
3 /
none
- Rat 3B between 1 and =
4 / 2
and 4
- Rat 3C between 0 and =
3 / 0
and 3
- Rat 3D between 0 and =
3 / 0
and 3
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- Increasing set or patc=
h size
promotes working memory processes relative to other search strategie=
s.
- Our rats seem to be able to recognize about 2 or 3 old objects.
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- Compare observed
distributions for finding all three jackpots with those for finding =
two
jackpots or only one jackpot from nine objects.
- Generate new theoretical distributions for number of choices to find=
the
first, second, or third jackpot based on no memory to perfect memory=
for
old objects.
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- Phase 3: 1st / 2nd / 3rd jackpot
- 2B: 6 - 8=
/ 3
– 7 / 0 – 4
- 2D: 7 - 9=
/ 7
– 9 / 6 – 8
- 3A: 6 - 8=
/ 2
– 6 / none
- 3B: 7 - 8=
/ 3
– 7 / 1 - 4
- 3C: 5 =
211; 8
/ 2 – 6 / 0 - 3
- 3D: 7 - 9=
/ 3
– 6 / 0 - 3
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- As rat finds more jack=
pots,
its performance for recognizing old objects declines
- Is this effect due to a loss in rat’s working memory capacity =
or
switching to other search strategies?
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