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IHTT
1
The Effect of Physiological Arousal on
Interhemispheric Transmission Time
Cathy Gouchie
Algoma University
Running Head: INTERHEMISPHERIC TRANSMISSION TIME
IHTT
2
The Effect of Physiological Arousal on
Interhemispheric Transmission Time
The rate at which information can be transmitted
between cerebral hemispheres may change, depending on
the circumstances. An increase in physiological
arousal may increase interhemispheric transmission
time (IHTT), the time taken for information to cross
from one hemisphere to the other. A brief review of
relevant neuroscientific facts and some previous IHTT
research will provide a better understanding of this
hypothesis.
Cerebral Hemispheres
The cerebrum of the human brain is divided into
two physically similar cerebral hemispheres. The
functions of the hemispheres are not symmetrical as
their appearance might indicate. In right handed
people, most language functions are concentrated in
the left hemisphere (including Broca's and Wernicke's
areas), though emotional inflection is provided by
the right hemisphere. The right hemisphere is
superior in recognizing faces, and in visual-spatial
and melodic skills. According to Segalowitz (1983)
IHTT
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the right hemisphere seems to be necessary for
integrating information and making inferences from
that synthesis.
In general, the left side of the body is
controlled by the motor cortex in the right half of
the brain and vice versa. Although uncrossed motor
pathways are known to exist, movement of the
individual limbs, especially their distal parts, are
the concern of the crossed pathways (Keypers, cited
in DiStefano, Morelli, Marzi, and Berlucchi, 1980).
Also some sensory information from one side of the
body is carried to the opposite hemisphere.
Visual reception is also crossed in the brain.
The optic fibers are partially crossed at the optic
chiasm. Because of this, all information projected
from the left visual field (to the left of a point
where both eyes are focused), is transmitted to the
right hemisphere. Information from the right visual
field is transmitted to the left hemisphere.
If the two sides of the brain were not able to
communicate, each would receive different visual
images and different sets of information from the
IHTT
4
environment. This is not the case since the
hemispheres are joined together by several bundles of
connecting fibers, the largest of which is the corpus
callosum. Normally, all information received by one
hemisphere is shared with the other hemisphere via
the corpus callosum. In this way, visual information
is integrated and only one image is seen.
Neural Transmission
The electrical nature of neural transmission
involves ions. At rest, the inside of a neuron
maintains a negative charge, due to an excess of
negative ions, with respect to the outside which
contains more positive ions. This resting potential
must be altered for a message to be transmitted. If
the change in potential is large enough, it passes a
threshold and an action potential is triggered. This
causes a sudden change in the permeability of the
cell membrane, allowing an influx of positive ions.
This change, the nerve impulse, spreads down the
length of the nerve fiber until it reaches a synapse.
The electrical charge in the fiber then returns to
normal.
IHTT
5
Each presynaptic terminal measures, in some way,
the number of signals arriving as electrical
impulses. When a sufficient number has arrived, the
terminal releases a neurotransmitter into the
synapse. This chemical crosses the synapse to
specialized receptors on the postsynaptic membrane of
the next neuron. Each receptor is specialized in
that it accepts only one of the many
neurotransmitters (Thompson, 1985).
Some neurotransmitters are excitatory and
increase the likelihood that a nerve impulse will be
created, while others are inhibitory and reduce the
chances of impulse firing. The rate at which a nerve
fires depends on the number and type of signals it
receives. The firing rate will increase if the
neuron receives many excitatory signals together; if
it receives many inhibitory signals, the firing rate
tends to decrease (Bootzin, Bower, Zajonc and Hall,
1986). The more rapidly a neuron fires, the more
neurotransmitters are released, therefore the greater
the effect on the receiving neuron.
IHTT
6
Through special techniques, locations of
specific neurotransmitter receptors in the brain have
been identified. For example, in a study of the
monkey brain by Snyder (1975, cited in Bignami and
Michalek, 1978), the highest density of acetylcholine
(ACh) receptors was found in the putamen, a part of
the basal ganglia. The lowest density was in the
optic chiasm, with fairly high levels present in
various areas of the cerebral cortex, thalamus and
hypothalamus, and a lower density in the corpus
callosum. However, as noted by Siggins and Bloom
(1981), most circuits of the cerebral cortex and
their neurotransmitters remain to be determined.
Alteration of neurotransmitter activity due to stress
Barry and Buckley (cited in Anisman, 1978)
described stress as stimulation that requires
behavioural and/or physiological adjustments. The
stimulation usually, but not always, represents a
threat to the animal's well-being. One effect of
stress is the arousal of the sympathetic nervous
system, leading to physiological change such as
increased heart rate, deeper and more rapid
IHTT
7
breathing, and a decrease in the galvanic skin
response. These changes mobilize the body for action
so the stressor can be better managed. This is
inferred by the Yerkes-Dodson Law, which says that
higher levels of arousal tend to improve performance
for tasks that are simple, or which require little
cognitive involvement. The more difficult the task,
the more it may be disrupted by high levels of
arousal.
Another consistent physiological change present
during stress is alteration in neurotransmitter
activity, including norepinephrine, dopamine,
acetylcholine and serotonin (Anisman, 1978). Several
factors, listed by Anisman, determine the extent of
these changes. Included are the severity of the
stressor, predictability of stress onset, and control
over stress onset or termination. Most stressors
examined in the studies reviewed by Anisman led to
changes in neuronal activity.
The information reviewed so far in this paper
suggests the following line of reasoning. A stressor
produces physiological arousal, including alterations
IHTT
8
in neurotransmitter activity, designed to manage the
stressor and increase survival of the organism. In
man and many other animals, motor control and
reception of sensory information for one side of the
body is primarily the concern of the opposite, or
contralateral, hemisphere of the cortex. Also, many
brain functions are lateralized to one hemisphere.
An decrease in IHTT, possibly due to changes in
neurotransmitter activity or rate of nerve firing,
would allow faster integration of vital information.
This would offer a distinct advantage to an
organism's survival under stressful situations.
Producing Physiological Arousal
As previously mentioned, physiological arousal
produces changes in neurotransmitter activity.
Physiological arousal can be induced in experimental
subjects by submitting them to loud (approximately 90
dB) white noise. The noise should be presented
continuously since, if bursts of intermittent noise
are not generated by the person himself, it may
distract him from what he is doing (Poulton, 1979).
Poulton stated that continuous noise can have
IHTT
9
different effects, depending on the nature of the
task. The increase in arousal, which accompanies
continuous noise, leads to improvement on simple
speed or vigilance tasks that respond well to
arousal. He pointed out that, while continuous noise
by itself does not appear to increase physiological
arousal for prolonged periods, having to perform a
challenging task in continuous noise may increase
arousal more than performing the task in quiet.
Measurement of IHTT
Most behavioural measures of interhemispheric
transmission time are based on reasoning originally
proposed by Poffenberger (1912, cited in Bashore,
1981). Simple reaction times (SRT) are measured in
response to a stimulus presented to one visual field
at a time. A stimulus presented to the right visual
field (RVF) is transmitted to the left hemisphere.
If a right-hand response (ipsilateral response) is
requested, the reaction time should be faster than if
the stimulus was presented to the left visual field
(LVF) and carried to the right hemisphere. In this
case, the information would have to be first
IHTT
10
transferred to the left hemisphere before a right-
hand response (contralateral response) could occur.
The difference in reaction times is assumed to be the
time required for the information to cross to the
other hemisphere (interhemispheric transmission
time).
Several factors have been proposed to account
for the difference in reaction times between
ipsilateral and contralateral responses. As a result
of his study, Wallace (1971) stated that the response
times were dependent on spatial compatibility of the
stimulus and response hand. He requested subjects to
cross their hands (crossed position) in half the
trials and found that reaction times were fastest
when the stimulus and response hand were on the same
side, regardless of whether the response was
ipsilateral or contralateral. He used a choice-
reaction time procedure, however, where one stimulus
requested a right-hand response, and a different
stimulus requested a left-hand response. This is a
different, more complex task than that of the simple
reaction time experiments. According to Bashore
IHTT
11
(1981), it is reasonable to assume a correspondence
amoung task complexity, cerebral activation and the
amount of information that must be conveyed between
the two hemispheres.
Berlucchi, Crea, DiStephano and Tassinari (1977)
conducted a similar study but used a simple reaction
time paradigm. In addition to the normal
presentation of the stimulus, a stimulus was
presented at three different visual angles for each
subject. The results showed that the advantage of
ipsilateral responses over contralateral responses
was consistent. This was true whether the hands were
in the correct anatomical position or in the crossed
position. They concluded that the time of difference
between ipsilateral and contralateral responses is
best attributed to a difference in the anatomy of the
neural pathways involved in the two kinds of
responses. Ipsilateral responses are integrated
within one cerebral hemisphere and contralateral
responses require interhemispheric cooperation.
Berlucchi and his fellow workers (1977) also
found that ipsilateral responses were faster than
IHTT
12
contralateral responses in both visual fields and for
all stimulus positions. This is in agreement with
the results of Berlucchi, Heron, Hyman, Rizzolatti
and Umilta (1971), where the delay between
ipsilateral and contralateral responses remained
constant regardless of the degree of eccentricity of
the visual stimuli.
Bashore (1981), after reviewing these many other
studies of IHTT, feels that sufficient research has
been done using SRT procedures to demonstrate
reliable estimates of IHTT. The average estimate of
IHTT using the SRT paradigm is approximately 3.0
msec.
Summary
If physiological arousal does cause a decrease
in IHTT, this change might be measured using a SRT
experiment. A noise of 90 dB, presented to some
subjects during the experiment, should induce
sufficient physiological arousal to allow any IHTT
differences to be measured.
IHTT
13
References
Anisman, H. (1978). Neurochemical changes elicited
by stress. In H. Anisman and G. Bignami (Eds.).
Psychopharmacology of aversively motivated
behaviour (pp. 119-161). New York: Plenum Press.
Bashore, T. (1981). Vocal and manual reaction time
estimates of interhemispheric transmission time.
Psychological Bulletin, 89, 352-368.
Berlucchi, G., Crea, F., DiStefano, M. and
Tassinari, G. (1977). Influence of spatial
stimulus response compatibility on
reaction time of ipsilateral and contralateral
hand to lateralized light stimuli. Journal of
Experimental Psychology, 3, 505-517.
Berlucchi, G., Heron, W., Hyman, R., Rizzolatti,
and Umilta, C. (1971). Simple reaction times of
ipsilateral and contralateral hand to
lateralized visual stimuli. Brain, 94, 419-430.
IHTT
14
Bignami, G. and Michalek, H. (1978). Cholinergic
mechanisms and aversively motivated behaviours.
In H. Anisman and G. Bignami (Eds.).
Psychopharmacoloqy of aversively motivated
behaviour (pp. 173-255). New York: Plenum Press.
Bootzin, R., Bower, G., Zajonc, R. and Hall, E.
(1986). Psychology today: An introduction. New
York: Random House.
DiStefano, M., Morelli, M., Marzi, C.A. and
Berlucchi, G. (1980). Hemispheric control of
unilateral and bilateral movements of proximal
and distal parts of the arm as inferred from
simple reaction time to lateralized light
stimuli in man. Experimental Brain Research, 38,
197-204.
Poulton,C. (1979). Composite model for human
perfo Rance in continuous noise. Psychological
Review, 86, 361-375.
Thompson, R.F. (1985). The brain. New York: W.H.
Freeman.
Segalowitz, S.J. (1983). Two sides of the brain.
New Jersey: Prentice-Hall.
IHTT
15
Siggins, G. and Bloom, F. (1981). Modulation of
unit activity by chemically coded neurons. In 0.
Pompeiano and C. Marsan (Eds.). Brain mechanisms
and perceptual awareness. (pp. 431-447). New
York: Raven Press.
Wallace, R.J. (1971). S-R compatibility and the
idea of a response code. Journal of Experimental
Psychology, 88, 354-360.
The Effect of Physiological Arousal on
Interhemispheric Transmission Time
Cathy Gouchie
Algoma University
IH1 1
Running Head: INTERHEMISPHERIC TRANSMISSION TIME
Abstract
The effect of physiological arousal on interhemispheric transmission
time (IH1 1') was investigated. Since physiological arousal produces
changes in neurotransmitter activity, these changes could result in a
decrease in IH1 1. IHTT was measured with a simple reaction time
(SRT) experiment using an IBM PC model 80 computer and customized
software. Physiological arousal was produced in 24 subjects through the
presentation of a loud (90 dB) white noise. Twelve were not submitted
to the noise. The results were inconclusive due to inaccurate
measurements of IHI'l . A possible reason for these results could be
the location of the stimulus. The light flash presented to subjects to
stimulate a response may have been situated too close to the centre of
the subject's field of vision rather than in the left or right visual fields.
IH 1 1
The Effect of Physiological Arousal on
Interhemispheric Transmission Time
Though the left and right cerebral hemispheres appear physically
similar, there are considerable and well-documented differences in their
functions (Segalowitz, 1983). Tactile and visual information is
transmitted directly to the hemisphere opposite to the side of the body
that received the information. Motor control of the limbs also rests
within the hemisphere on the opposite side of the body.
The hemispheres are joined together by several bundles of
connecting fibers, the largest of which is the corpus callosum Any
advantage gained by one hemisphere through lateralization of function,
or any sensory information coming into only one hemisphere, is shared
with the other hemisphere by transmitting information across the corpus
callosum
The rate at which information can be transmitted between cerebral
hemispheres may change, depending on the circumstances. An increase
in physiological arousal may decrease the interhemispheric transmission
time (IH I 1'), the time taken for information to cross from one
IH I I
hemisphere to the other. Vital information could therefore be
integrated more quickly, offering a distinct advantage to an organism's
survival under stressful situations.
IH I I can be measured using a simple reaction time (SRT)
experiment. This paradigm is based on reasoning originally proposed by
Poffenberger (1912, cited in Bashore, 1981). Simple reaction times are
measured in response to a stimulus presented to only one visual field at
a time. A stimulus presented to the right visual field (RVF) is
transmitted to the left hemisphere. If a right hand response (ipsilateral
response) is requested, the reaction time should be faster than if the
stimulus were presented to the left visual field (LVF) and carried to the
right hemisphere. In this case, the information would have to be first
transferred to the left hemisphere before a right hand response could
occur (contralateral response). The difference in reaction times is
assumed to be the time required for the information to cross to the
other hemisphere (interhemispheric transmission time-IHTT).
Several behavioral studies have been performed on measurements of
IHTT. After reviewing many of these studies of IHTT, Bashore (1981)
felt that sufficient research had been done using SRT procedures to
IHI I
demonstrate reliable estimates of IH'I 1. The average estimate is
appc,..,.(imately 3.0 insec.
Based on previous am research, it should be possible to comparedifferences in IHTT under different conditions using the SRT paradigm.
If physiological arousal can be induced in some subjects, a decrease in
IHTT compared to subjects under normal conditions may be detected.
Method
Subjects
Thirty-six psychology students (eight male, twenty-eight female) at
Algoma University took part in this study on a voluntary basis. They
were all right-handed, with normal or corrected vision as tested on the
Lomb Orthorater. They ranged in age from 18 to 45 years.
,,:„Jed for their participation with bonus marks in one
of their psychology courses. All were treated in accordance with the
"Ethical Principles of Psychologists" (American Psychological
Association, 1981).
Procedure
was seated with the head positioned so a fixed viewing
distance of 17 cm from the computer screen was maintained. This
ensured that the stimulus was presented at the proper visual angle. The
IH11
ghL tad rested of the table with the index finger prepared to hold
down the response button. Subjects were instructed to focus on the
fixation point at all times, and to lift their finger from the button as
quickly as possible whenever a stimulus appeared, whether it was to the
left or right of the fixation point.
Stimuli were presented on the display screen of an IBM PC Model
30 computer utilizing customized software. A small fixation spot
remained present in the centre of the screen throughout the session.
Before each trial, the computer displayed written instructions to press
the button and hold it down when ready to proceed with the trial. Once
the button was pressed, and after a delay varying randomly between 500
and 1500 cosec (to discourage anticipatory responding), the stimulus
symbol was presented for 25 msec subtending 4 of visual angle to
either the left or right of the fixation point. The presentation and
randomization of the left-right trial sequence was controlled by
computer. Any reaction times (RT) that fell outside the range of 100-
1000 rnsec were excluded since very short RT may be due to
anticipation and long RT may be the result of lapse of attention (Milner
and Lines, 1982). Release of a microswitch attached to the computer
terminal served as the response. The time from onset of stimulus to
IH'I I
release of the button was measured and recorded by the computer as
the reaction time.
Each test session consisted of 20 practice trials, followed by 6 blocks of
40 trials each. There was a rest period of several minutes between each
block. All subjects were asked to wear earphones throughout the
experiment. Physiological arousal was produced in some of the subjects
by submitting them, through use of the earphones, to a loud (90 dB),
continuous white noise. Poulton (1979) pointed out that the increase in
arousal, which accompanies continuous noise, leads to improvement on
simple speed or vigilance tasks. Noise of 90 dB during the reaction time
experiment should, therefore, produce sufficient physiological arousal to
allow any IHTT advantages, derived from increased arousal, to be
measured. Twelve of the subjects (early noise group) were submitted to
the noise after completion of the second block. Another twelve (late
noise group) were submitted to the noise after the fourth block. The
final twelve served as a control group and wore the headphones but
were not exposed to the noise.
IL recorded every ten seconds during the practice and
experimental trials using a Inque pulse monitor model PU-701 and the
values were averaged for each block. During the interval between
IH11
blocks blood pressure was measured with a Copal digital
sphygmomanometer UA-271.
Results
The mean RVF response times were subtracted from the mean LVF
times to produce a measure of IHTT per block for each subject.
However, as Figure 1 shows, many of the IH I I values calculated in this
way were negative, a reversal of the expected results. Most
Insert Figure 1 about here
subjects produced both negative and positive values, indicating that the
times measured were not actually interhemispheric transmission times.
The effect of noise on the physiological arousal of the subjects can
be seen from Figure 2. Changes
Insert Figure 2 about here
in pulse rate, calculated by subtracting mean pulse rate/block from the
mean pulse rate for the practice trials, declined in the control group as
the experiment progressed. The same trend was observed in the late
9
noise group until the noise was introduced. At this point the heart rate
leveled off. Pulse rate in the early noise group remained relatively
constant throughout the experiment and higher than for all other groups.
Blood pressure did not change significantly during the experiment.
Discussion
Due to the invalid measurements of IH1 1', it cannot be determined
from this experiment whether or not physiological arousal increases the
rate that information is transmitted between hemispheres.
As predicted by Poulton, a continuous noise of 90 dB did increase
the physiological arousal in the experimental subjects. The task
required of the subjects was basically a long, eventually monotonous one
and, as indicated by the pulse rate of the control subjects, physiological
arousal decreased as the experiment proceeded. The late noise
experimental group also began to relax until the introduction of the
noise after the fourth block of trials. The pulse rate then ceased to
decline, remaining instead at the level it was before the noise was
activated. The pulse rate of the early noise group did not decline
indicating the subjects in this group did not relax, probably attributable
to the noise they were listening to.
IH1T
10
Figure 3 illustrates the results expected from this study if
physiological arousal does increase IHTT. Since the physiological
arousal level of the
Insert Figure 3 about here
control group decreases, the time it takes for a message to cross from
one hemisphere to the other may take slightly longer. The late noise
group would also show an increased IH I at the beginning since
physiological arousal in that group also decreased at the beginning of
the experiment. The early noise group would be expected to have fairly
constant measurements of IH'1 1 since their level of arousal remained
relatively constant throughout the experiment.
re vresearch on IHTT using the simple reaction time paradigm
produced reliable measurements of around 3 msec (Bashore, 1981).
Milner and Lines (1982) also found consistent results measuring IHTT
with a simple reaction time paradigm using computers. Since the
current study was based on the theory and methodology of these
previous studies ( Berlucchi, Crea, DiStefano, and Tassinari, 1977;
Berlucchi, Heron, Hyman, Rizzolatti, and Umilta, 1971; DiStefano,
11
Morelli, Marzi and Berlucchi, 1980), the measurements of IH I I should
have been similar. However, many of the values were negative
indicating that for some reason the procedure did not measure IH I I as
intended. If negative values were consistently obtained, this would mean
that the contralateral response was faster for some reason. However,
positive and negative values were evenly mixed.
There is no explanation yet as to why the methods designed for use
in this study failed to measure IHTT. A possibility is that the stimuli
were not displayed at a great enough visual angle to ensure presentation
to only one visual field at a time If this is the case, it is an adjustment
easily made for replication of the experiment in the future.
IHTT
12
References
American Psychological Association (1981). Ethical
principles of psychologists. American
Psychologist, 36, 633-638.
Bashore, T. (1981). Vocal and manual reaction time estimates of
interhemispheric transmission time. Psychological Bulletin, 89, 352-
368.
Berlucchi, G., Crea, F., DiStefano, M. and Tassinari, G. (1977).
Influence of spatial stimulus response compatibility on reaction time
of ipsilateral and contralateral hand to lateralized light stimuli.
Journal of Experimental Psychology, 3, 505-517.
Berlucchi, G., Heron, W., Hyman, R., Rizzolatti, and Umilta, C.
(1971). Simple reaction times of ipsilateral and contralateral
hand LO lateralized visual stimuli. Brain, 94, 419-430.
DiStefano, ivl., Morelli, M., Marzi, C.A. and Berlucchi, G.
(1980). Hemispheric control of unilateral and bilateral
movements of proximal and distal parts of the arm as inferred from
simple reaction time to lateralized light stimuli in man.
Experimental Brain Research, 38, 197-204.
IH' I I
13
Milner, A. and Lines, C. (1982). Interhemispheric
pathways in simple reaction time to lateralized
light flash. Neuropsychologia, 20, 171-179.
Poulton,C. (1979). Composite model for human performance in
continuous noise. Psychological Review, 86, 361-375.
Segalowitz, S.J. (1983). Two sides of the brain. New Jersey: Prentice-
Hall.
IH'I I
14
Figure Caption
Figure 1. Mean IHTT measurements per block of trials.
Figure 2. Mean changes in pulse rate per block of trials.
Figure 3. Diagram of expected IH 1 1 measurements.
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