Taxes,
trophics, habituation, and sensitization
There are three
important types of reflexes for our study: Kinesis, Taxis, and Modal
Action Patterns
(MAPs). Kinesis is a reflexive increase in movement as a result of
an eliciting
stimulus. Touch a worm and it wiggles, sometimes jumping about wildly.
Taxis is a reflexive
movement that is more directed. When a paramecium goes
swimming along and
suddenly bumps into a wall, it's cillia immediately go into
reverse. Rats and
most rodents, are thigmotaxic, meaning that they move with as
much of their bodies
in contact with a surface as possible. In a burrow or wall of a
house most the body
remains in contact with a surface. As the mouse runs around
in your kitchen, it
attempts to remain close to one wall, as if rubbing its' side against
the wall. MAPs, or
modal action patterns (some texts call these FAPs for fixed
action patterns) are
a type of reflex that involves more than one behavior in a
particular sequence.
The sequence may be fixed, meaning it always occurs in a
particular order, or
as is more often the case, the sequence is usually in a particular
order, but may vary
somewhat.
.Presentation of the
stimulus alone. => habituation, sensitization
(non-associative learning).
2.Presentation of the stimulus in relation to another stimulus.
=> classical
conditioning (associative learning)
3.Presentation of the stimulus in relation to some of the
organisms own
behavior. => operant conditioning (associative learning)
Habituation and Sensitization
.Habituation (definition) --
Given that a particular stimulus elicits a response,
repeated applications of the
stimulus result in decreased response. The decrease is
usually a negative
exponential function of the number of stimulus
presentations.
2. Spontaneous Recovery --
If the stimulus is withdrawn following habituation
training, the response tends
to recover over time.
The vigor of an elicited response
can be decreased or increased
through the mechanisms habituation
and sensitization (a decrease is
due to habituation and an increase
is due to sensitization).
General principlesf
regulation
There are two principles of
regulation according to Domjan: 1)
Regulated variables (for example
your level of arousal or your core
body temperature) are kept in a
"target range" (i.e., within acceptable
limits). 2) as a general principle
of regulation by
anyone other than Domjan.)
Effects of the
repeated presentation of an eliciting
stimulus
Habituation is the decrease in
response strength with repeated
exposure to a particular eliciting stimulus. Sensitization
is the increase
in response strength with repeated
exposure to a particular stimulus. (I
would like to say here, that the
discussion of habituation and
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sensitization is VERY important! The reason I
say this is that we
can see these effects easily in our
everyday lives. I will illustrate
this in class with DEMO#1. Although
Domjan does not make this
clear, both these effects are very basic
types of learning.)
Characteristics of
habituation effects
Effects of stimulus change. Lots of
things affect habituation (That is
to say: The exact characteristics of
the eliciting stimulus (S) have
an effect on the size or magnitude
of the elicited response (R) with
repeated exposure to that same
stimulus.). Most importantly,
habituation is reduced by any
difference between the habituated
stimulus and the test stimulus.
Stimulus generalization of
habituation refers to the increase
in a previously habituated response,
under any circumstances where the
stimulus is changed. (All of this is
not quite as simple as Domjan makes
it seem. "Habituation" refers
to a decrease in the strength of an
elicited response with repeated
elicitation by an identical
stimulus. However, since even the
slightest change in the stimulus
attracts the attention of the subject,
any habituated response gets
stronger (or less habituated)
whenever a new – or even a slightly
changed – stimulus appears
(even if the new stimulus is very
similar to the one that was
originally habituated. The graph in
Figure 3.2 reflects the fact that
a previously habituated stimulus (*)
elicits a greater amount of
habituation (i.e., smaller magnitude
response) than even a slightly
different stimulus (i.e., test
stimuli anywhere left or right of * in fig.
3.2). Furthermore, the size of the
difference in the presented
stimulus from the habituated test
stimulus, the less habituation that
will occur (i.e., stronger responses
left and right of * in fig. 3.2).
Effects of time. The only thing
essential to recognize in this section is
that habituated responses, in
general, tend to recover the longer the
time since the last occurrence or
presentation of the habituated
stimulus. The recovery of the
response strength with time is called
spontaneous recovery. (Save for
later: We will discover later that
spontaneous recovery (as well as
other habituation phenomena)
occurs in other types of learning
situations also. With spontaneous
recovery, the key is the passage of time without
presentation of the
stimulus (S) or elicitation of the
response (R). Can you think of an
experiment that could be used to
test whether spontaneous
recovery depends on the absence of
the S or the absence of the
R?)
Effects of stimulus intensity. The
rate of change of the response (R)
with repetition of the stimulus (S)
is greater the weaker the stimulus
and, conversely, is less the stronger
the stimulus.
Effects of exposure to a second
stimulus. Look carefully at Fig.
3.4. Dishabituation is somewhat like
spontaneous recovery, except
in this case the recovery of the
previously habituated response
depends on the presentation of a second (i.e., distracting)
stimulus
rather than the passage of time.
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Effects of time after
a dishabituating stimulus. (We are really
getting down to fine points here!)
Basically, what Domjan is saying is
that for a distractor to produce
dishabituation, it has to be presented
immediately before the next test
trial with the habituated stimulus. If
there is a long delay between the
distractor and the next test trial,
there won’t be as much
dishabituation.
Characteristics of
sensitization effects
A type of
sensitization in humans
If you have ever burnt one on your fingers you might have noticed
that if you run your hands
under warm water, your burnt finger
will hurt, even if it is the
day after you burnt it. The warm water
normally does not cause any
pain, but after burning your finger, it
is
sensitized. Now the warm water causes pain.
Cocaine-sensitization
High doses of cocaine
produce a variety of behaviors,
including increased activity
and stereotyped behaviors
like head bobs. Repeatedly
giving an animal high doses
of cocaine also leads to
tolerance, where more and more
of this drug of abuse is
needed to produce an effect. If
animals are given lower
doses of cocaine, however, no
obvious responses occur to
the first dose. If the animal is
given this same low dose
intermittently, for example
once every week, it develops
an increased sensitivity to
the drug, as seen by
increased locomotion and the
emergence of head bobs.
Because these behaviors
emerge only after repeated
drug administration,
something in the brain must
be changing to produce the
sensitization. Independent
student research projects in
my and Dr. Coughlin’s labs
have examined the role of
other drugs in modifying the
development and/or
expression of cocaine
sensitization.
Domjan is trying in
this section to argue that sensitization is the opposite of
habituation. However,
as he notes, there are key differences. I think it is better
to think of
sensitization as a special case of habituation in which the response
fails to decrease, or
may actually increase in strength with repeated stimulation.
In fact,
sensitization is much less common than habituation and typically only
occurs if the animal
or person is irritated or aroused in some way, either by the
extreme intensity of
the test stimulus itself, or by something else in the
environment –
including the animal’s or person’s own internal environment. It
follows that
individuals may differ in their response to a repeated stimulus,
depending on whether
they find it or the situation irritating.
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Mechanisms of
habituation and sensitization
(What does Domjan
mean by "mechanisms" or "underlying mechanisms?")
The S-R system and
the state system
The dual-process
theory aims to explain both habituation and sensitization within
one framework (Such a
framework is sometimes called a "theory" or a "model"
or a
"paradigm" depending on how "grand" the theorists want to
be. This is
our first encounter
with theory but certainly not our last.) This section simply
points out the
assumption of this particular dual-process theory that there are two
presumed sub-systems:
1) the S-R sub-system is responsible for producing a fixed
response to a
stimulus (e.g., a reflex). 2) the "State System" is responsible for
modifying the state
of the S-R system (thus accounting for the obvious variability of
the response as a
function of the variability of the situation (e.g., stimulus timing,
stimulus intensity,
distractors, etc.) The theory itself merely says that the actual
habituation or
sensitization "phenomena" depend on the additive effects of two
processes (one of
which is assumed to act on the State System - the sensitization
process and one of
which is assumed to act on the S-R System - the habituation
process). These two
"processes" get added together to produce the actual
observed
"phenomena."
Implications of the
duel-process theory
Whatever you do,
don't let this theoretical discussion "spook" you. Theorists
love to observe some
nice reliable behavioral phenomena, such as habituation
and sensitization,
then come up with all kinds of imaginary ways that these
phenomena might
occur. In this particular case, dual-process theory starts from
a very simplistic or
"imaginary nervous system." It then goes on to make this
imaginary nervous
system operate in just the right way to produce the
phenomena that it
seeks to "explain." As Domjan points out, this theory is very
successful in
explaining most of the short-term effects of repeated stimuli and
arousing stimuli. I,
personally, like theorizing because it allows me to see all the
ways that you might
make an imaginary system work to produce just the effects
you expect. On the
other hand, some people don’t like all the uncertainty this
introduces about how
the "real" systems work. We really need both kinds of
people in science --
those who guess (theorists) and those who check to see if
the guesses are
correct (empiricists). This is how science progresses.
Previous studies of
infant attention, learning, and memory have revealed that
certain stimulus properties may increase an
infant's arousal or excitation level,
thereby increasing responsiveness and
facilitating the encoding and processing of
information. In a series of experiments aimed
at identifying stimulus determinants of
sensitization, we examined visual responses
from 4-month-old infants to spectral
lights. Habituation data were obtained from
92 full-term infants separated into one
of five groups. Each group viewed either a
broadband white light (correlated color
temperature ≃ 2800 K) or one of four
different spectral lights (d = 470,
510, 570, or 650 nm) approximately
corresponding to the elemental hues blue,
green, yellow and red, respectively, for
adults with normal trichromatic vision.
Stimuli were equated in luminous efficiency
for a standard infant observer. Stimulus
fixation was recorded for twelve 10-s
presentations, each separated by 10-s
interstimulus intervals (ISIs). The results
show that mean fixation times to the red
and green lights were significantly greater
than those for the blue and white light.
Mean fixation time for the yellow light was
also reduced (significantly) to the red
but not the green light. These results
suggest that the chromatic properties of red
and green spectral lights may be more
sensitizing to infants than those of the blue,
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Habituation
Sensitization
