PSYC 301L Winter 06: Lab Write-Up #1
Body Weight Experiment
Your rats will undergo two distinct feeding regimes. Before you came into their life, your rat
was fed ad libitum (free-feeding phase)s for a least 10 days. This phase will end for each rat
when its weight remains stable for five days. The “maximum weight” for each rat (the average
weight during the 5 day stable period) is referred to as the rat’s 100% weight. Today you will
calculated the 100% weight for your animal and then calculated 85% of that weight in order to
obtain the rat’s maintenance weight (85% of its 100% weight).
In the second phase (restricted-feeding phase) each rat will be fed 10g of food per day or the
number of grams that the rat is under its 85% weight, whichever is greater, each day. You will
begin this process today. For the purposes of this lab write-up, you will be given the weight data
from one of the rats, so everyone will base their results and discussion section on the one group
of data. In order to complete this assignment you will be given:
1. a “daily weight and feeding chart” that shows the weight of the rat for ten days. Here,
dates have been replaced with day number. The rat was free-fed for the first 10 days,
then, the restricted feeding phase began on day 11. For each day beginning with day 11,
fill in the amount of food that should have been weighed and fed to the rat (7 pts). Do not
forget to take into account whether or not the rat was fed in the operant chamber (you can
tell the rat was “run” in the operant chamber if a “before” weight is listed).
2. an introduction describing the body weight experiment. (You may be surprised that we
are calling this an experiment, but in fact the procedure that we used to control the body
weight of the rat is similar to the way in which many of these types of experiments begin:
We provide different phases of training, each for some period of time, then look for
changes over time in some dependent variable, and relate these changes to the training
phases).
Complete the APA formatted lab write-up by doing the following:
1. Title page (APA format) (5pts)
2. Write up a methods section. Here you will be outlining in detail how this
experiment was done as well as details about the animal and equipment used.
Here you will need to follow the standard format as outlined in the APA manual
(ie., sections to include: subject, apparatus, procedure) (10 pts).
3. Prepare Figure 1. Create a graph showing the body weight on the vertical axis
and days (numbered 1-20) on the horizontal axis. On days that the rat was run,
use the before weight and ignore the after weight. For the other days, use the after
weight. Separate the figure into two panels with a dashed vertical line,
corresponding to the two treatment phases. Label the two panels and indicate the
rat’s 85% weight on the second panel with a dashed horizontal line (remember the
format necessary for including a figure in an APA formatted paper. In the figure
caption include the subject’s number, the variables manipulated and measured,
and just enough about the procedure that the reader can grasp the basic ideas of
the experiment (10 pts).
4. Write a results (10 pts) and discussion (8 pts) section for this experiment.
Although your figure will effective reflect the results of the experiment, you must
still need to communicate the results in writing. Since a statistical analysis will
not be performed you will not be reporting such things as F values, t values, alpha
level, etc. However, you will can report systematic trends in the data, and relate
these trends to the two feeding regimes. Write in the past tense and use objective
language. Do not list raw data, but include some actual values to make your
description concrete. For example, you might want to include the starting weight,
the 100% weight (when it was reached), the 85% weight (when it was reached),
etc. Conclude this paper by providing discussion, which interprets the data in
terms of what was said in the introduction. Try to connect back to the
“experimental hypothesis”, which was stated in the last sentence of the
introduction provided. (Hint: What have your observations of your rat’s behavior
and health suggested about the adequacy of the feeding protocol?) In addition,
limitations and or problems in the experiment and suggestions for future research
should be included.
4. Submit your work stapled in the following order:
a. Title Page (5 pts)
b. Method (10 pts)
c. Results (10 pts)
d. Discussion (8 pts)
e. Figure (10 pts)
f. Weight and feeding chart with the amounts fed filled in (7 pts)
Total = 50 pts
BACKGROUND
The Body Weight of a Rat on Two Feeding Regimens
In behavioral research in which food is provided as reinforcement, it is customary to
maintain animals in a state of food deprivations. The obvious rationale for this is that in order
for food to serve as an effective reinforcer, the animal must be sufficiently motivated to consume
the food. The deprivation level is typically achieved by allowing the animal free access to food
for some period of time, and then gradually reducing the animal’s weight to 85% of the
maximum weight obtained during ad libitum feeding (free-feeding).
Although a 15% reduction in body weight may seem extreme, this is a rather moderate
level of deprivation. Hineline (1986) noted that a comparable method of determining the
maximum free-feeding weight of a human would be to provide “continuous and easy access to
an open, well stocked refrigerator and not much else” (p. 124). The implication here is that
animals maintained on an ad libitum diet are likely to be overweight. Hineline (1986) observed
that while free-feeding, food related behaviors are replaced with other patterns of behavior.
Since wild animals must work hard to secure food, they should do so only when motivation is
somewhat high; therefore, they would probably self-regulate their weights to something well
under the maximum free-feeding weight.
The purpose of the present experiment was to investigate the effect of two eating regimes
on the weight of the animal and to determine whether the feeding procedure produces an
adequate motivational state for operant behavior training with food reward without endangering
the animal’s health or welfare.