Acquisition and Retention in Rats: Comparing Olfactory and Visual Cues as Facilitators of Learning

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Acquisition and Retention in Rats Comparing
Olfactory and Visual Cues as Facilitators of
Learning   Cathryn Chandler and
Katherine Wetzel Randolph-Macon
Womans College Lynchburg, VA 24503
Introduction The sand maze is a less aversive
spatial task that can be employed as an
alternative to the water maze in some studies
(Gotthard, 2006). While the water maze requires
rats to swim in a pool of water to locate a
hidden platform (Morris, 1981), the sand maze
requires rats to dig in a pool of sand to
retrieve buried cereal rewards (Hanson, 2003).
In experiments using rats in the sand maze,
visual cues are often used as facilitators for
acquisition and retention of operant tasks. The
vision of the rat has evolved to accommodate for
the nocturnal nature of the species in the wild,
as a means of avoiding predators. Thus, only the
ability to distinguish natural colors (i.e.
black, white and brown) is the extent of the
visual complexity of the rat. (Park, 1940). The
rats sense of smell is considerably stronger than
their visual accuity, therefore it is
hypothesized that the rats will better learn
operant tasks in the sand maze when directed by
olfactory cues as opposed to visual cues.
Results In earlier trials both groups took longer
to learn the task, yet in later trials the mean
latency for the Olfactory Group decreased. For
both groups, rats demonstrated a quadrant
preference that can only be attributed to chance
for the correct quadrant during
testing. Latency Latency to retrieve the reward
was measured for each rat during each of 7 trials
Olfactory Group M1 21.41, SD1 6.3,
M2 30.61, SD2 40.46, M3 31.09, SD3 11.6
M4 36.55, SD4 37.95 M5 103.56, SD5
67.58 M6 68.53, SD6 99.00 M7 25.31, SD7
13.41. Visual Group M1 22.15, SD1 12.57 M2
15.53, SD2 8.99 M3 52.24, SD3 29.36 M4
31.42, SD4 21.43 M5 53.41, SD5 49.38 M6
60.09, SD6 31.03 M7 67.8, SD7 41.92). A
paired samples t-test was run comparing Olfactory
Trials 5 and 7, Visual Trials 5 and 7, and
Olfactory Trial 7 to Visual Trial 7 , Quadrant
Preference A one-sample t-test was conducted for
each group to determine whether preference for
the correct quadrant was exhibited. Neither the
Visual Group, t(3) .652, p .561 (two-tailed)
or theOlfactory Group, t(3) -2.400, p .096
(two-tailed) demonstrated statistical
significance.
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Method Subjects The subjects were 6-month-old,
male Long-Evans rats (N8) divided into two
groups of 4 rats. Rats were reduced to and
maintained at 85 of their free-feeding weights
one week prior to experimentation. Water was
available ad libitum. Apparatus The sand maze was
a plastic pool (36 inches wide by 6 inches deep)
filled with a sand/crushed Froot Loops (FL)
cereal mixture that was 2 inches deep
(approximately 11 ounces of FL was crushed and
mixed with 100 pounds of play sand to make the
mixture). Four white index cards, three on which
a white circle was taped, one on which a black
circle was taped, were used for the visual cues
trials. Four white index cards were used for the
olfactory cues trials, three of which were blank,
one on which a 1 diameter circle of milk and
honey scented lotion was applied. The maze was
elevated 36 inches off the floor. Procedure Each
rat was a member of either the Visual or
Olfactory groups, and was placed in the sand maze
and required to find Froot Loops cereal (FL). The
FL were located in one of the four quadrants (NW,
SW, SE, NE), coinciding with an intra-maze cue -
either the card with the black circle (for the
Visual Group) or the scented card (for the
Olfactory Group). Rats were started from a
consistent location, the South end of the maze,
for each trial. After finding the reward on any
given trial, the rat was allowed to consume
approximately one to two FL prior to termination
of the trial (the low number of FL was a
preventative measure to avoid satiation.) Rats
were handled prior to shaping. The location of
the FL and the correct cue card was rotated for
each Trial in a counterclockwise direction,
beginning at NW (i.e. NW for the first rat in the
trial, SW for the second, and so forth.) Seven
trials were conducted the FL were buried deeper
with each succeeding trial. During Trials 1 and 2
the FL were completely exposed during Trials 3
and 4 the FL were partially exposed (shallow
buried.) During Trials 5, 6 and 7 the FL were
completely buried. A final probe trial was
conducted where no FL were buried, and each
participant spent exactly 2 minutes in the maze.
The time spent in each quadrant was recorded in
order to determine quadrant preference.

• Discussion
• The mean latency of the rats increased as they
  were learning to locate the FL. Once the task was
  learned,
• the mean latency steadily declined for the
  Olfactory Group, but did not for the Visual
  Group.
• Rat 20 took an substantially long time
  (114047) during Trial 4, creating outlying data
  which would have skewed our results. Therefore
  this latency record was not included the
  analysis.
• Observations indicated that the rats could smell
  the FL even when completely buried. Subsequent
  research could be conducted on the depth at which
  FL must be in order that rats cannot detect the
  scent.
• Lack of time was also a potential factor in
  success of acquisition and retention. Had many
  more trials been conducted, the results may have
  indicated more marked differences in the learning
  of the two groups.

References Gotthard, G.H. (2006). Experimental
Psychology Learning Laboratory Lab
Manual. Randolph-Macon Womans College. Hanson,
G.R. (2003).  The sand maze An appetitive
alternative to the Morris water maze
(Doctoral dissertation, Kent State
University, 2003). Dissertation Abstracts
International, 63, 4958.   Park, O.
(1940). Nocturnalism The development of a
problem. Ecological Monographs, Vol. 10,
3, 485-536. Morris, R.G.M. (1981). Spatial
localization does not require the
presence of local cues. Learning and Motivation,
12, 239-260.