Download EXTENDED PRIMARY AND HIGHER ORDER CONDITIONING OF

EXTENDED PRIMARY AND HIGHER ORDER
CONDITIONING OF EARTHWORMS
by
THOKtAS ALVIN FIELDS, B.A,
A THESIS
IN
PSYCHOLOGY
Submitted to the Graduate Faculty
of Texas Tech University in
Partial FulfiTi.,.'--nt of
the Requirements for
the Degree of
MASTER OF ARTS
Approved
August, 1970
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ACKNOWLEDGMENTS
I am deeply indebted to Dr. Sam L. Campbell for his
direction of this thesis. Without his patience, critical
direction, and personal involvement, this research might
never have been completed.
I would also like to express my graditude to Mr.
Robert 0. Haynes for his help in constructing and maintaining my apparatus. Mr. Haynes was also invaluable in
the computer compilation of the data.
IT
CONTENTS
Page
ACKNOWLEDGEMENTS
ii
LIST OF TABLES
iv
LIST OF FIGURES
v
I.
INTRODUCTION
1
Instrumental (Operant) Learning Studies . 1
Classical (Pavlovian) Conditioning
Studies
3
Purpose
II.
7
METHOD
9
Subjects
9
Apparatus
9
Procedure and Experimental Design . . . .
III.
RESULTS AND DISCUSSION
14
19
First-Order Conditioning (Phase One). . . 19
Second-Order Conditioning (Phase Two) . . 22
and Re-Conditioning (Phase Three). . . 22
Second-Order Extinction (Phase Four). . . 26
First-Order Extinction (Phase Five) . . .
lY.
CONCLUSIONS
26
30
REFERENCES
32
m
LIST OF TABLES
Table
Page
I. Stimulus Configurations Per Group
and Number of Trials Per Day in
Each Phase
IV
16
LIST OF FIGURES
Figure
1.
2.
3.
4.
5.
6.
7.
8.
Page
Experimental chamber with access door
open, showing conditioning trough.
Portable control panel is to right
and connector plug to Automatic Programming Instrumentation to lower
left
10
Close-up of conditioning trough on
grid platform showing electrodes
and leads at either end, resting
on millimeter grid paper and supported by fiberboard base with
speaker mounted below
12
Number of conditioned responses
per group per day during firstorder conditioning
20
Average latency of conditioned
response per group per day during
first-order conditioning
21
Number of conditioned responses
per group per day for secondorder conditioning
23
Number of second-order conditioned
responses per group per day on
test trials during second-order
conditioning
25
Number of second-order conditioned
responses per group per day
during second-order extinction
27
Number of first-order conditioned
responses per group per day
during first-order extinction
29
CHAPTER 1
INTRODUCTION
The earliest reported behavioral studies of earthworms was executed in 1889 by Hesse (Jaeobson, 1963).
Hesse reported that bodily
contractions, interpreted as withdrawal responses, occurred with decreases in illumination.
Smith (1902),in a replication and extension
of Parker and Arkin's research (1901),investigated the effects of temperature, odors, light, and tactual stimulation on contractual behaviors
of worms.
Shortly thereafter, investigators began utilizing instru-
mental operations in the investigation of worm behavior (Yerkes, 1912;
Heck, 1920; Robinson, 1953; and Datta, 1963).
Instrumental (Operant) Learning Studies
In 1912, Yerkes demonstrated that the earthworm could discriminate
between an arm of a T-maze which lead to an earth-filled goal box and an
arm which lead to electro-shock.
Heck (1920) replicated Yerkes' study
but used a larger number of subjects and three varieties of earthworms.
He found that the worm required 100-200 training trials to discriminate
the correct arm of the T-maze, and an additional 50-70 trials to learn
a reversal of the original discrimination.
Robinson (1953) questioned Yerkes' conclusion that stimuli other
than those normally associated with a maze were required just prior to
encountering shock, to facilitate learning.
1
Using a T-maze, Robinson
reported that there were two distinct phases in the learning of an
operant task by earthworms. The first phase occurred about trial 50
when "running time" significantly increased.
Robinson described the
worm at that phase as reacting negatively to all portions of the maze.
By "negative", he could be referring, quantitatively, only to the temporal changes in response properties. But Robinson concluded that the
first phase decrements were attributable to classically conditioned
withdrawal responses which hindered the acquisition of instrumental
(operant) responses. He also suggested that when training was carried
beyond the first phase, no stimuli other than those ordinarily in the
maze were required for learning.
Datta (1963) taught a position habit in a T-maze by presenting
shock at the terminus of one arm and the home container at the terminus
of the other arm.
Her conclusion: a one-minute intertrial interval re-
sulted in the same degree of learning as a five-minute intertrial interval.
Longer intertrial intervals, such as 25 minutes, resulted in no
learning. Also progressive improvement was obtained after several
training trials.
Other studies utilizing instrumental operations to investigate
earthworm behavior include Swartz(1930), Wherry and Sanders (1941),
Bharueha-Reid (1956), Krivanek (1956), and Arbit (1960).
There have been several studies which proposed to show that the
behavior described in the above experiments was not attributable to
learning but to some other behavioral process such as pseudoconditioning
or sensitization.
Fisehel (1933) was unable to train worms to use tactual cues which
were provided in a Y-maze. However, the assumption was made that the
tactual cues would be the only relevant cues in the situation and no
attempt was made to control other relevant stimuli.
Fraser (1958) in a much more comprehensive investigation questioned
methodological aspects of prior studies after failing, himself, to obtain learning in a T-maze.
He proposed that the failure by earlier ex-
perimenters to specify pretraining turning preferences and then to train
the worms appropriately to the non-preferred side, substantially weakened
their claims that learning had been obtained.
Fraser also suggested
that the criteria of learning utilized were so low (weak or permissive)
as to admit factors other than learning to be more relevant to obtained
changes in behavior.
Kirk and Thompson (1967) obtained no evidence of learning as measured by "crawl-time" in a straight alley, and simply questioned whether
instrumental learning by earthworms was possible.
Classical (Pavlovian) Conditioning Studies
With the exception of three studies in the 1930's (Copeland, 1930;
Copeland and Brown, 1934; and Raabe, 1939), all research involving Pavlovian conditioning of earthworms has developed since 1959. Perhaps
this is attributable, as suggested by Bitterman (1960), to the difficulty of recording classical responses. Certainly, the tender membranes
of the worm cannot be operated upon with the crude meehaneial devices
so often required when working with a new species (i. e., one for which
standard laboratory instrumentation is not available), nor can it be
expected at this time, that institutions regulating psychological research would invest in researches about an organism so diverse from man.
Copeland (1930) was the first to use classical conditioning techniques as a basic paradigm in earthworm research. The worm was housed in
a water-imnersed tube and obtained food from the water by characteristic,
bodily-involved, ingestive movements. Copeland preceded the presentations of food by an increase in illumination.
Within five trials, food-
gathering responses occurred at the onset of the light. Copeland and
Brown (1934), using the same general experimental technique, substituted
a tactual cue (touch to the anterior end of the worm) for the light cue.
Again, reliable conditioned responses were obtained after a few trials.
Raabe (1939) found that shock, tactual cues, and vibrations could
serve as unconditioned stimuli. By preceding any of these unconditioned
stimuli with an increase or decrease in illumination, a conditioned
withdrawal response ("retraction" would be the better term to use, since
we refer to classical reflexes, and "withdrawal" might be confused with
instrumental behaviors) could be established in 10-20 trials.
Raabe also argued that contiguity was critical in the establishment
of the conditioned response. He found the most effective conditioned
stimulus-unconditioned stimulus interval to be one-half to one second.
Intervals as long as three seconds were less effective; intervals of four
and zero seconds were ineffectual.
Finally, he found that the onset of
light was more successful as a conditioned stimulus than was the offset
of light.
Ratner and Miller (1959) published what Jaeobson (1963) called the
first study of true classical conditioning in the earthworm.
Ratner and
Miller conditioned a one-eighth to one-quarter inch withdrawal response
to vibration with light serving as the unconditioned stimulus (UCS).
They used a 50 second intertrial interval. The vibratory conditioned
stimulus (CS) was on for six seconds with the illuminative UCS on for the
terminal two seconds. One hundred conditioning trials preceded extinction. The earthworms showed a significant increase in the conditioned
response (CR) to the CS during training and a significant decrease of
CR to the CS during extinction. Three control groups were used.
The
first control received 100 trials of six seconds of vibration without an
UCS. The second control received 100 trials of four seconds of observation without the CS or UCS. The third control received 105 trials consisting of 70 light and 35 vibration trials. The two second UCS was
given in blocks of ten trials followed by a block of five six-second
CS trials.
Bitterman (1960) mentioned pairing a neutral stimulus with shock
which produced a conditioned withdrawal reaction in the worm.
He at-
tempted to measure the response on a kymograph with little success. He
did note that the response was clearly visible to the naked eye.
Herz, Wyers and Peeke in 1963 evaluated the effects of partial reinforcement on a classically conditioned response. Using a vibratory
CS, one group received the UCS of light on 100 percent of the acquisition
trials. The second group received the UCS on a random 50 percent of the
acquisition trials. There was no difference between groups during acquisition but the partial reinforcement group showed increased resistance to extinction.
Peeke, Herz and Wyers (1964) used light as an UCS and vibration
as a CS to investigate the effects of partial reinforcement, and amounts
of acquisition training on resistance to extinction.
The CR was initially
described as a one-half to one inch withdrawal of the anterior segments,
or stoppage and/or rearing of the anterior segments of the body.
But
since the rearing response occurred more reliably, it was subsequently
used as the critical response.
were utilized:
(1)
Six conditioning and two control groups
100 percent reinforcement with 50 acquisition trials,
(2) 100 percent reinforcement with 100 acquisition trials, (3)
percent reinforcement withl50 acquisition trials, (4)
100
50 percent rein-
forcement with 50 acquisition trials, (5) 50 percent reinforcement with
100 acquisition trials, (6)
50 percent reinforcement with 150 acquisi-
tion trials; the control groups were a sensitization control where the
UCS was omitted on every trial and the pseudoconditioning control where
the CS was presented alone for the first ten trials and then the UCS was
presented alone for the next five trials. All groups were trained over
three days. The results indicated no differences among groups with
respect to the ratio of CR's to total number of acquisition trials.
But the partial reinforcement group showed increased resistance to extinction when compared to the continuous reinforcement group.
Wyers, Peeke and Herz (1964) replicated the study using light as
the UCS and vibration as the CS. Again, they investigated the effects
of partial reinforcement.
The results were the same:
the partial re-
inforcement group showed increased resistance to extinction.
Morgan (1965) and Morgan, Ratner and Denny (1965) attempted to
measure a Galvanic Skin Response (GSR) to onset of illumination. The
worm was stitched to a damp sponge with the GSR electrodes mounted
through opposite ends of the worm.
Five groups of subjects were used.
The first group consisted of dead controls used to adjust the apparatus
The other groups received 480, 180, 80, or zero footeandles of illumination. The authors obtained reliable indications of Galvanic Skin
Response. As the intensity of the stimulus increased, the intensity
of the response increased. The 480 footcandle group made the largest
responses and showed the slowest adaptation to the stimuli. However,
all subjects adapted to the stimuli in three to five trials.
Evans (1966) has argued that evidence for the classical conditioning of earthworms is, at best, tenuous, and that adequate controls for
pseudoconditioning and sensitization have not been utilized.
He noted
that earthworms respond to many stimuli with withdrawal responses, and
that response magnitude varies directly with stimulus magnitude. His
assertation accompanied a study in which he was unable to find evidence
of learning after 150 conditioning trials.
Purpose
A first objective of the present study is to evaluate Evans' assertation regarding the lack of evidence for classical (Pavlovian) conditioning of earthworms.
I intend an extensive study utilizing far more
than 150 conditioning trials, utilizing adequate controls for both
8
sensitization and pseudoconditioning, and, further, evaluating any conditioning results with subsequent extinction operations.
A second objective of this study is to inquire whether higherorder classical conditioning can be obtained with earthworms - no evidence of an attempt to do so appears in the literature.
Pavlov (1960) described a conditioning program whereby an original
CS was used as a substitution for an UCS in the conditioning of a second
CS. A dog was conditioned to salivate to the sound of a metronome. A
black square, which elicited no salivation, was held in front of the dog
and the metronome sounded. After ten trials, the dog salivated to the
presentation of the black square. Pavlov referred to this as second
order classical conditioning.
CHAPTER II
METHOD
Subjects
Twenty-four earthworms (Annelida-Lumbricus terrestris) varying
In length from four to five inches were obtained from a local bait
shop. They were housed individually in one pint plastic containers
filled with a moist mixture of coffee grounds, grass, moss, and earth.
The containers were stored on semi-dark shelves at room temperatures
ranging from 75 to 78 degrees F.
Apparatus
Exploratory studies indicated that S^s could not survive frequent
handling. Accordingly, apparatus was designed so that each of six Ss
could be placed in its own experimental chamber and remain (without
handling) for a series of conditioning trials over a daily training
session. To initiate appropriate combinations of stimuli (electroshock, light, and/or vibration) and to record S^'s response, the experimenter carried a programming panel which could be plugged into each
experimental chamber successively (Fig. 1). Through the programming
panel, behavior was recorded and the selection, timing, and sequencing
of stimuli were automatically controlled by instrumentation housed in
an adjoining, sound-proofed room. Moving from chamber to chamber with
the control panel permitted maximal use of recording and control facilities while minimizing handling of S^s and allowing for adequate intertrial intervals.
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Conditioning trough: The conditioning trough was the bottom half
of a clear plastic toothbrush case to which electrodes were attached
at opposite ends (Fig. 2). It rested on a grid-covered fiberboard
platform, to the bottom of which was bolted a four by six inch oval
speaker. The platform, in turn, rested on sponge-rubber supports to
Isolate it from extraneous vibratory stimuli. Prior to each day's
training session, Ss were rinsed in room temperature tap water and
the troughs moistened.
Experimental Chamber: The experimental chambers were twelve inches
wide by six inches deep by twenty-eight inches high, and were painted
flat black.
Each chamber housed a trough unit with its appropriate
sources for shock and vibratory stimuli and had a 200-watt lamp mounted
18 inches above the trough platform for photic stimulation.
A hinged
door provided access to the interior and contained an observation port
In its face. The observation port was covered with X-ray film and constant interior illumination was provided by a one-watt red lamp mounted
nine inches above the trough.
Hess (1924) found this photic stimulation
to be subliminal for earthworms.
Stimulus Properties: During first-order conditioning of all groups,
the unconditioned stimulus was a .16 milliampere electro-shock of one
second duration.
It was preceded by a 200-watt light for two seconds,
and both light and shock were present during the third second of each
trial.
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During second-order conditioning of the experimental S^s, a 60
cycle vibratory stimulus was presented for two seconds and then overlapped the light for an additional second. Various combinations and
orders of presentation of these stimuli were used with the several control groups described below.
Excepting extinction trials and the occa-
sional test trials interspersed during conditioning, every trial consisted of the three-second presentation of a stimulus overlapping a
stimulus of different modality during the last second.
In all instances,
whether conditioning, test or extinction trials, 90 seconds elapsed
between trials for a given S^.
The unconditioned response to shock is characteristically a violent
contraction and coiling.
In this study if S^s were elongated at the ini-
tiation of a trial, contraction of both the anterior and posterior ends
was considered evidence of an adequate conditioned response.
If the S
were already partially coiled, then additional constriction of the coil
and withdrawal of the head into the coil was considered a conditioned
response.
Response Definition and Recording Procedure: Because of difficulties previously encountered in attempts to automatically record respondent reflexes of earthworms (Bitterman, 1960), Ss' responses were observed by the experimenter and were recorded by both an Ester!ine-Angus
event marker and a Foringer print-out counter when the experimenter depressed the "response" switch on his portable control panel.
In the
analysis of records, a response was judged to be a conditioned response
14
only If It occurred during the first second of the initial stimulus the stimulus to be conditioned, whether in first-order or second order
conditioning. The simultaneous and automatic recording of onset of the
various stimuli on separate event-marking channels indicated the latency
of each response.
As a check on the reliability of the experimenter's discrimination
of conditioned responses, other observers were given a verbal description of the experimental procedure and conditioned response characteristics. They were then asked to make independent judgements as to whether
a conditioned response (CR) occurred on given trials. A Pearsonian
correlation of .91 was obtained between judgements of the experimenter
and independent observers.
Procedure and Experimental Design
S^s were run in four waves per day, six S^s per wave (one S^ for each
experimental chamber).
The v/ave to which S^s were assigned was randomly
determined, but remained the same for given S^s throughout training so as
to control for elapsed time between sessions.
The 24 S^s were equally but randomly assigned to one of four groups
prior to the first-order conditioning to which all Ss were subjected.
Assignment to four different groups was intended to provide information
regarding variability of conditioning trends among groups of six subjects
during first-order conditioning.
Were the results sufficiently variable,
they might preclude expectations of differences attributable to various
treatments provided during succeeding phases of training.
15
During first-order conditioning, all S^s were given 20 trials per day
with light as the to-be conditioned stimulus and shock as the unconditioned stimulus.
Following the 16 days of conditioning which provided
a total of 320 trials, and despite the yery similar and overlapping
performances during days 12-16, S^s were again equally but randomly
as-
signed to four groups and given an additional session of first-order
conditioning to evaluate the comparability of the basal performance with
which various groups entered the second phase of training.
The four groups of subjects were trained in five phases, with
stimulus operations varying among groups and from phase to phase. These
variations were intended to provide controls for sensitization and
pseudoconditioning, and tests of conditioned response strength by subsequent second- and first-order extinction. Table 1 indicates the
stimulus operations for various training phases of the four groups.
The groups are designated Experimental (Group I ) , Light Sensitization Control (Group II), Random Control (Group III), and Shock Control
(Group IV).
The phases can be generally described as: Phase One, first order
conditioning (340 trials over 17 days), identical for all subjects as
described above; Phase Two, second-order conditioning or control for
same (200 trials plus 60 test trials); Phase Three, first-order re-conditioning or conditioning to vibration as a conditioned, new firstorder, stimulus for Groups II and IV, respectively (80 trials over four
days with no test trials interspersed); Phase Four, second-order
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extinction (Three seconds of vibration for 80 trials over four days).
Identical for all groups; Phase Five, first-order extinction (Three
seconds of light for 200 trials over 10 days). Identical for all groups
excepting Group II which served as a control for extinction of other
Ss and continued to receive light and shock conditioning during Phase
Five.
Rationales for the various stimulus operations utilized among the
groups and training phases can best be specified in connection with the
Results of this report, but a detailed description of operations used in
Phase Two and Phase Three conditioning of the control groups (II, III,
and IV) follows.
It should be understood that when reference is made
to two stimuli which are hyphen-connected, the first stimulus was of
three seconds duration and overlapped the second stimulus by one second.
Light Sensitization Control (Group II): During Phase Two these Ss
received 20 light-vibration pairings and four vibration (test) trials
per day. The order of stimulus pairings was intended to determine if
light sensitization would obtain (i.e., if light-vibration pairings
could produce a second-order conditioned response during vibration test
trials) or maintain a first-order conditioned response to lights.
Following 15 days of Phase Two conditioning, these Ss were retrained
during Phase Three with first-order conditioning procedures.
Random Control (Group III): ^s received random combinations of all
stimuli with the exceptions of vibration-light and vibration-shock to
evaluate whether other combinations of stimuli might produce or sensitize
18
a second-order conditioned response. They were given five trials each
of shock-light, shock-vibration, light-vibration, and light-shock
pairings, randomly dispersed among four test trials of vibration only.
These stimulus operations contained through 15 days of second-order
conditioning (Phase Two), and, as a control, through four additional
days of Phase Three conditioning.
Shock Sensitization Control (Group IV): During Phase Two these
S^s received 20 shock-vibration pairings randomly interspersed among
four test trials per day. These stimulus operations were used to
evaluate whether shock-vibration pairings would sensitize (produce)
a conditioned response during the test trials. Following 15 days
of Phase Two conditioning, the Phase Three conditioning comprised
four days of first-order vibration-shock pairings to determine
whether vibration could serve as an adequate conditioned stimulus.
CHAPTER III
RESULTS AND DISCUSSION
First-Order Conditioning (Phase One)
The reliable results of first-order conditioning is indicated
in Fig.'s 3 and 4. Total number of conditioned responses per day
for each group is negatively accelerated and approaches asymptote
at about 115 CRs per daily training session. There is little
variability but considerable overlap among groups, and especially
during the last nine sessions when asymptotic performances produce
more than 90 percent CRs per total trials. Krusal-Wallis tests do
not provide sufficient evidence of differences among groups during
the first or last four conditioning sessions (p is far greater than
.05 for H=1.312 and H=1.022).
But a Mann-Whitney U test (Siegel,
1956) indicates a significant difference between number of CRs during the first versus the last four days of conditioning (z=2.32, p .05)
Randomization of all ^s into four "new" groups after the sixteenth
daily session (see B, Fig. 3) resulted in almost identical total
performance among groups during the seventeenth conditioning session.
Finally, latency of CR data as graphed in Fig. 4 supposts the above
analysis.
19
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Second-Order Conditioning (Phase Two)
and Re-Conditioning (Phase Three)
Re^P<^nses to the first stimulus on conditioning trials: The
experimental S^s (Group I) show little evidence of second order
conditioning by their response to vibration on the vibration-light
trials during Phase Two and Phase Three (Fig. 5). But the criteria
of a CR required that it have a low latency (occur during the first
second of vibration) and may have been unduly severe. The critical
evidence for or against second-order conditioning should appear on
the interspersed three second test trials described below.
The light sensitization control (Group II) demonstrates typical
extinction of a first-order conditioned response once light-vibration
pairings were substituted for light-shock pairings. Total CRs decline from about 100 to 10 over 15 days of Phase Two conditioning.
But the original first-order CR is rapidly re-established when lightshock pairings are re-introduced during four days of Phase Three
conditioning.
The random control (Group III) maintained a relatively high
and consistent number of responses to the initial stimulus under
all four stimulus permutations (five pairings each per daily
session).
23
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Since the shock sensitization control conditioning operations
consisted of shock-vibration pairings (Group IV), responses to the
initial stimulus would be unconditioned responses and are not
graphed in Fig. 5 for Phase Two. But when it became apparent from
test trial data (see Fig. 6) that sensitization had not occurred,
these S^s were provided first-order conditioning pairings of vibration-shock to establish that vibration can serve as an adequate
CS. The rapid conditioning of CRs to vibration during Phase Three
training is evident at A, Fig. 5, where total number of CRs per
session rises from zero to 75 over four daily sessions. This acquisition function is similar to that of original light-shock
conditioning in this study and to the vibration-light conditioning
data of Ratner and Denny (1959).
Responses on Test Trials: The critical variable for evaluating
second-order conditioning in this study is total number of CRs per
group over the four test trials provided during second-order (Phase
Two) conditioning, when vibration alone was presented for three
seconds.
All groups evidenced some degree of sensitization or pseudoconditioning during the first few days, but the experimental group
alone continued to respond at a relatively high though variable
level (see Fig. 6 ) . A Krusal-Wallis test for overall significance
among groups provided a statistic which was slightly less than that
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required for significance at the .05 level (obtained H=7.27, while
H=7.82 at p=.05). To locate the principle differences between
groups, Mann-Whitney U tests were calculated and indicated that they
were between Groups I and III and between Groups I and IV (U=60.5
for former, U=59.5 for latter, U=61 at p=.10), but barely significant at the p=.10 level of significance.
Second-Order Extinction (Phase Fourj^
During Phase Four, vibratory stimulation alone was presented
for three seconds, 20 trials per day over four days. Responses
to vibratory stimulation by Group II (Light sensitization control)
and Group III (random control) were negligible, as they had been
during Phase Three training (see Fig. 7 ) .
Group IV having been first-order conditioned by vibrationshock pairings during the prior Phase Three training showed a
marked predictible decline in CRs when vibration alone was presented.
However, consistent with evidence of second-order conditioning
of the experimental group (I), there was an orderly decline from
17 to five total responses over the four extinction sessions.
First-Order Extinction (Phase Five)
The group II S^s which had been re-conditioned to first-order
light-shock conditioning during Phase Three and were unaffected
by exposure to vibration during Phase Four, were maintained on firstorder, light-shock conditioning as a control for the extinction
27
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which all other groups underwent by the presentation of light
alone. The overall differences among their performance (see Fig. 8)
and that of other groups is statistically significant (KrusalWallis test yields H=14.04 with p<.01). Some rationale might be
proposed for the most interesting absence of overlap among extinction curves of Groups I, III, and IV. While appropriate
statistical tests would probably demonstrate the reliability of
differences in these trends, statistical comparisons have not
been made and any possibly relevant conclusions would be post
hoc and not necessarily central to this thesis.
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CHAPTER IV
CONCLUSIONS
Considering such relevant factors as number of conditioning
trials, controls for sensitization and pseudoconditioning, reconditioning and extinction controls, this study provides substantial evidence of first-order light-shock and vibrationshock conditioning of earthworms.
While there have been implications that previously obtained
data bearing on classical conditioning of annelida is somehow
spurious (Evans, 1966), this experiment was not primarily designed to test the possibility of first-order conditioning of
earthworms which was already felt acceptably demonstrated; rather
it was intended to evaluate the possibility of second-order conditioning.
Evidence of second-order conditioning obtained in this study
was very nearly statistically reliable according to contemporary
"standards" of the scientific community.
But there is no statistic
designed to evaluate the complex relationship among changing
sequences of conditioning operations as employed in the present
experiment. While considerable laboratory-control operations
30
JW-
31
were maintained in the collection of data reported, it is proposed that slight modifications in experimental design, especially
sample size, might produce confident conclusions that earthworms
can be second-order conditioned.
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