# Impairment of Spatial Performance by Environmental Noise

Authors: Mohammad Ali Gheraat; Nasser Naghdi; Bahram Jalaei; Pouneh Mokhtari; Farid Rezaei Moghadam; Elaheh Soleimannejad; Leila Eidi Abarghani
Journal: Scholarly Research Exchange
 (2009)

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## Abstract

We examined the effects of noise on acquisition and retention of the spatial memory task in equal and unequal context in adult male rats. The natural noise in Azadi football stadium was recorded and measured by sound level meter instrument and set in high (HI), moderate (MI), and low (LI) intensities, 86, 64, and 47 decibels A (dbA), respectively. Rats were trained in Morris water maze (MWM) for 3-consecutive-day program and at day 4 visible and probe tests were done under one of the above noise intensities. The retention was evaluated at day 7 on the basis of equal and unequal noise exposure situation. Escape latency, traveled distance, and swimming speed were recorded and used for subsequent analysis. Our results showed significant increases in the escape latency and traveled distance by increasing the noise intensity during acquisition period, and also retention test in equal noise situation. Furthermore, retention test in the group that was under HI noise during both training period and retention test escape latency and traveled distance compared to the groups which was under HI noise during training period and LI or MI noise during retention test (HI-LI or HI-MI).


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## Body

## 1. Introduction

Noise is one
of the problems which affects some aspects of human life. For example, noise
impairs human task performance most likely in the case of unexpected bursts of
noise presented during tasks, whether it involves the continuous intake of new
information [1, 2],  and also the psychomotor
task impaired by brief experimentally imposed noise in human [3].
In contrast of these studies, It has been shown that addition of an appropriate
amount of noise can improve signal detection in a nonlinear system called
stochastic resonance [4]; human hearing and the ability of
encoding temporal information can increase by noise
[5–7].
Nevill et al. [8] found that crowd noise
influenced referee’s decisions at favor of the home team. In marine life (e.g.,
in cetaceans), the general increase in underwater noise and the use of sonar
have been associated with behavioral and pathological changes  in diving mammalians exposed to such an
environment [9, 10].Studies on the short-term effects of imposed noise on school-age
children’s performance in classroom environments have found no effects of a
range of noise levels on writing task performance [11], and different
kinds of sound on performance of easy and difficult arithmetic problems
[12], and also imposed experimental noise on oddity task
performance. Adverse effects of 55–78 dbA noise have
been found on recognition memory task [13]. Several studies
found long-term effects of traffic noise on auditory discrimination
[14],
reading, and attention [15].Some theories explaining the effects of noise are primarily based
on the researcher's perception of the role of adaptation [13], but Glass and Singer [16] have reported that autonomic reactivity
does not always adapt with brief noise stimulation (continuous 80 dbA). Prevalent
theoretical approaches often account for noise effects using the concepts of
arousal or distraction [17–20]. Positive and negative effects are
suggested to be as a reason of distraction-arousal arising from extra-auditory
systemic responses (physiological and intellectual) to stimulate nervous system
through auditory channels
[21].However, different kinds and levels of noise can have various
effects on retention test. The present study was performed to investigate this
idea that whether various intensities of noise can act as differential positive
and negative impacts on acquisition and retention of a spatial memory task in
equal; when the intensity of noise during training period is the same as
exposed noise intensity during retention performance task, and unequal noise contextual
situations in rats.


## 2. Materials and Methods

### 2.1. Animals

Adult male albino Wister rats
(12 weeks old), weighting 250–300 gr, were
obtained from the breeding colony of the Pasteur Institute of Iran. They were housed
four per cage in a temperature and light-controlled room under 12 hours: 12 hours
light-dark cycle (light at 07:00 am) with free access to water and food.
Experiments were carried out in a room where only the MWM was placed in
standard conditions and took place at 13:00–16:00.


### 2.2. Noise Regulation

We measured intensity of noise
obtained from a football stadium with sound level meter (B&K 2250, UK)
instrument, when the stadium was full of spectators (about 100 000 people). The
intensity of noise was about 105 dbA in an extremely noisy situation, and about
95 dbA in moderate situation, and also 69 dbA in silence times. At first, we
recorded this natural sound from football stadium and compared to the hearing
system of rats, then we set the intensity of noise for high and moderate
situations in 86 dbA and 64 dbA. We regulated the acoustic system in these
intensities by Cool-Edit 2000 Software (designed by Gold soft company, UK) at
a stable frequency.


### 2.3. Apparatus

The MWM task was consisted of a
dark circular pool (140 cm in diameter, 55 cm height) filled with water (20±1°C)
to a depth of 25 cm. A transparent Plexiglas platform (11 cm in diameter) was
located 1 cm below the water surface in the center of one of arbitrarily
designed north-east (NE), south-east (SE), south-west (SW), or north-west (NW) orthogonal
quadrants. The platform provided the escape from the water. The room, where
water maze was placed, was surrounded by extra maze cues such as racks, a door,
a watch, and pictures on the walls which were kept in fixed positions, respectively,
around the swimming pool. So rats were allowed to locate the escape platform
hidden below the water by using these cues. A video tracking system and a PC
computer with software developed for monitoring and storing the position of the
rat in the water maze was used. Thus, the required time to reach the platform (escape
latency) and the swimming path (travelled distance) were recorded.


### 2.4. Procedure

The spatial memory task was defined
as finding the hidden platform in the MWM. All rats were given a daily session
of two blocks (each block consisted of 4 trials) with 5 minutes interval
between blocks for 3 days in the training period. During all experiments, the
platform was located in a fixed position in the middle of SW quadrant. Each
trial involved placing the rat in the pool, close to and facing the wall in one
of the four equal quadrants (North, South, East, or West). Rats were allowed to
swim freely until they found the platform. If a rat failed to find the platform
within 90 seconds, the experimenter placed the rat on it. The intertrial
interval was 30 seconds, during which the rat remained on the platform. The rat
was taken directly from the platform to the new starting point which was changed
from trial to trial in a quasirandom order. So each starting point was used
once in each session of 4 trials. All animals were exposed to the defined noise
in their group (as described below) during training period and also probe,
visible, and retention tests.We divided rats into 3 groups: low-intensity
noise group (LI = control) was trained under natural noise (47 dbA) (n = 8), while
moderate-intensity noise (MI) and high-intensity noise (HI) groups were trained
under 64 dbA and 86 dbA (n = 7 per group) noise intensities, respectively. For
the first 3 consecutive days, rats were trained in MWM along with noise
exposure. At the day 4, probe and visible tests were done. For the Probe test,
the platform was removed away in the MWM and let the rats to swim and look for
platform and SW quadrant. 60 minutes after doing the probe test, the platform was
covered by aluminum foil and placed 1 cm above the water surface in the SE
quadrant and visible test was done. This procedure is believed to provide
information on the possible nonspecific effects involving motor, visual, or
motivational abilities. At day 7, the retention test was done when the platform
was placed in the SW quadrant and it was similar to the training day program in
blocks and trial numbers of sessions while noise was exposed. If the exposed noise
during retention test was similar to ones in the training period, then the test is called “equal;”  if it
wasn’t similar, then it is
called “unequal” retention test.


### 2.5. Statistical Analysis

The data analyzed by one-way
analysis of variance (ANOVA), followed by post hoc Tuky's test and also we usedt-repeated measure. All results have shown as mean ± SEM. In all statistical
comparisons, P<.05 was considered as significant difference.


### 2.6. Experiments

Experiment 1
The aim of this experiment was
to determine the effect of low-intensity (LI) noise exposure during acquisition
period and retention test on MWM performance. In this experiment, rats were
trained in LI noise for 3 training days according to the procedure. Visible and
probe tests were held in day 4.  Retention
test was performed under equal (LI) and two unequal (MI and HI) noise conditions.
It should note since environmental sounds in the experimental room were similar
to LI noise intensity (approximately 47 dbA), so we used the group under LI-exposed
noise during both training period and retention test (LI-LI) as the control
group.Experiment 2
The aim of this experiment was
to determine the effect of MI noise exposure during acquisition period and
retention test on MWM performance. In this experiment, rats were trained in MI noise
for 3 training days according to the procedure. Visible and probe tests held in
day 4. Retention test was performed under equal (MI) and two unequal (LI and
HI) noise conditions.Experiment 3
The aim of this experiment was
to determine the effect of HI noise exposure during acquisition period and
retention test on MWM performance. In this experiment, rats were trained in HI noise
for 3 training days according to the procedure. Visible test and probe tests
held in day 4. Retention test was performed under equal (HI) and two unequal
(LI and MI) noise conditions.


## 2.1. Animals

Adult male albino Wister rats
(12 weeks old), weighting 250–300 gr, were
obtained from the breeding colony of the Pasteur Institute of Iran. They were housed
four per cage in a temperature and light-controlled room under 12 hours: 12 hours
light-dark cycle (light at 07:00 am) with free access to water and food.
Experiments were carried out in a room where only the MWM was placed in
standard conditions and took place at 13:00–16:00.


## 2.2. Noise Regulation

We measured intensity of noise
obtained from a football stadium with sound level meter (B&K 2250, UK)
instrument, when the stadium was full of spectators (about 100 000 people). The
intensity of noise was about 105 dbA in an extremely noisy situation, and about
95 dbA in moderate situation, and also 69 dbA in silence times. At first, we
recorded this natural sound from football stadium and compared to the hearing
system of rats, then we set the intensity of noise for high and moderate
situations in 86 dbA and 64 dbA. We regulated the acoustic system in these
intensities by Cool-Edit 2000 Software (designed by Gold soft company, UK) at
a stable frequency.


## 2.3. Apparatus

The MWM task was consisted of a
dark circular pool (140 cm in diameter, 55 cm height) filled with water (20±1°C)
to a depth of 25 cm. A transparent Plexiglas platform (11 cm in diameter) was
located 1 cm below the water surface in the center of one of arbitrarily
designed north-east (NE), south-east (SE), south-west (SW), or north-west (NW) orthogonal
quadrants. The platform provided the escape from the water. The room, where
water maze was placed, was surrounded by extra maze cues such as racks, a door,
a watch, and pictures on the walls which were kept in fixed positions, respectively,
around the swimming pool. So rats were allowed to locate the escape platform
hidden below the water by using these cues. A video tracking system and a PC
computer with software developed for monitoring and storing the position of the
rat in the water maze was used. Thus, the required time to reach the platform (escape
latency) and the swimming path (travelled distance) were recorded.


## 2.4. Procedure

The spatial memory task was defined
as finding the hidden platform in the MWM. All rats were given a daily session
of two blocks (each block consisted of 4 trials) with 5 minutes interval
between blocks for 3 days in the training period. During all experiments, the
platform was located in a fixed position in the middle of SW quadrant. Each
trial involved placing the rat in the pool, close to and facing the wall in one
of the four equal quadrants (North, South, East, or West). Rats were allowed to
swim freely until they found the platform. If a rat failed to find the platform
within 90 seconds, the experimenter placed the rat on it. The intertrial
interval was 30 seconds, during which the rat remained on the platform. The rat
was taken directly from the platform to the new starting point which was changed
from trial to trial in a quasirandom order. So each starting point was used
once in each session of 4 trials. All animals were exposed to the defined noise
in their group (as described below) during training period and also probe,
visible, and retention tests.We divided rats into 3 groups: low-intensity
noise group (LI = control) was trained under natural noise (47 dbA) (n = 8), while
moderate-intensity noise (MI) and high-intensity noise (HI) groups were trained
under 64 dbA and 86 dbA (n = 7 per group) noise intensities, respectively. For
the first 3 consecutive days, rats were trained in MWM along with noise
exposure. At the day 4, probe and visible tests were done. For the Probe test,
the platform was removed away in the MWM and let the rats to swim and look for
platform and SW quadrant. 60 minutes after doing the probe test, the platform was
covered by aluminum foil and placed 1 cm above the water surface in the SE
quadrant and visible test was done. This procedure is believed to provide
information on the possible nonspecific effects involving motor, visual, or
motivational abilities. At day 7, the retention test was done when the platform
was placed in the SW quadrant and it was similar to the training day program in
blocks and trial numbers of sessions while noise was exposed. If the exposed noise
during retention test was similar to ones in the training period, then the test is called “equal;”  if it
wasn’t similar, then it is
called “unequal” retention test.


## 2.5. Statistical Analysis

The data analyzed by one-way
analysis of variance (ANOVA), followed by post hoc Tuky's test and also we usedt-repeated measure. All results have shown as mean ± SEM. In all statistical
comparisons, P<.05 was considered as significant difference.


## 2.6. Experiments

Experiment 1
The aim of this experiment was
to determine the effect of low-intensity (LI) noise exposure during acquisition
period and retention test on MWM performance. In this experiment, rats were
trained in LI noise for 3 training days according to the procedure. Visible and
probe tests were held in day 4.  Retention
test was performed under equal (LI) and two unequal (MI and HI) noise conditions.
It should note since environmental sounds in the experimental room were similar
to LI noise intensity (approximately 47 dbA), so we used the group under LI-exposed
noise during both training period and retention test (LI-LI) as the control
group.Experiment 2
The aim of this experiment was
to determine the effect of MI noise exposure during acquisition period and
retention test on MWM performance. In this experiment, rats were trained in MI noise
for 3 training days according to the procedure. Visible and probe tests held in
day 4. Retention test was performed under equal (MI) and two unequal (LI and
HI) noise conditions.Experiment 3
The aim of this experiment was
to determine the effect of HI noise exposure during acquisition period and
retention test on MWM performance. In this experiment, rats were trained in HI noise
for 3 training days according to the procedure. Visible test and probe tests
held in day 4. Retention test was performed under equal (HI) and two unequal
(LI and MI) noise conditions.


## 3. Results

Our results were based on the
data which was acquired in acquisition period and retention tests in equal and
unequal noise situations. The escape latency, traveled distance, and swimming
speed were recorded. In all experiments, the swimming speed had no significant differences.
So we do not report details of speed results here.


### 3.1. Training Period

#### 3.1.1. Hidden Platform Trials
(Day 1 to 3 between Groups)

Figure1(a) shows the results of training in the three levels
of noise during training period and visible test. There were significant
differences  in escape latency at day 1 [
F
(2, 20) = 14.48, P<.05],
day 2 [F (2, 20) =  27.62, P<.05], and day 3 [F (2, 20) = 10.53, P<.05]  between three groups. These significant
differences in the escape latency were between LI group with HI group in day 1
(P = .00), day 2 (P<.05), and also day 3 (P<.05).Effects of various
intensities of noise during training period on escape latency in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between different
intensities and LI.
(a)(b)For traveled distance, there were significant differences at
day 1 [F (2, 20) =  22.43, P<.05], day 2 [F (2, 20) =
83.7, P<.05], and day 3 [F (2, 20) = 19.44, P<.05]  between groups. At day 1 (Figure 2(a)), there were significant differences
between LI group with MI group (P<.05) and also HI group (P<.05).
At day 2 and 3, it showed a significant difference between LI group with HI
group (P<.05).Effects of various
intensities of noise during training period on traveled distance in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between
different intensities and LI.
(a)(b)Experiment 1: Performances in Exposure of Li Noise during Training Period, Equal and Unequal Retention Tests
There were no significant
differences between the results of day 1 to 3 in LI noise (Figures1(b) and 2(b)).
Figures 3(a) and 4(b) show there were significant
differences between equal and unequal retention tests (for escape latency F (2, 20) =14.1, P<.05 and also for traveled distance,
F  (2, 20) = 16.7, P<.05); it was between equal (LI-LI) and
unequal (LI-HI) retention tests (P<.05 for both escape latency and traveled
distance). In the visible and probe tests, there were no significant
differences for escape latency and traveled distance.Different effects of
noise exposure on escape latency. (a) Equal (LI-LI) and unequal, moderate (LI-MI)
and high (LI-HI) intensities, and retention tests in LI training group; (b) equal
(MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group;  (d) equal retention tests for LI, MI, and HI
training groups.*P<.05 shows a significant difference between
different intensities with equal group in a to c and LI group in d.
(a)(b)(c)(d)Different effects of
noise exposure on traveled distance. (a) Equal (LI-LI) and unequal, moderate
(LI-MI) and high (LI-HI) intensities, and retention tests in LI training group;
(b) equal (MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group; (d) equal
retention tests for LI, MI, and HI training groups.*P<0.05 shows a
significant difference between different intensities with equal group in a to c
and LI group in d.
(a)(b)(c)(d)Experiment 2: Performances in Exposure of Mi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed MI noise (Figures1(b) and 2(b)).
Figures 3(b) and 4(b) show there were significant differences between equal and
unequal retention tests (for escape latency, F  (2, 20)  = 17.3, P<.05
and for traveled distance, F (2, 20) = 18.7, P<.05); which
it was between equal (MI-MI) and unequal (MI-LI) retention tests (P<.05
for both escape latency and traveled distance). In the visible and probe tests,
there were no significant differences for escape latency and traveled distance.Experiment 3: Performances in Exposure of Hi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed HI noise (Figures1(b) and 2(b)).
Figures 3(c) and 4(c) show there were significant differences between equal and
unequal retention tests (for escape latency, F (2, 20) = 22.7, P<.05,
and for traveled distance, F (2,20) = 23.08, P<.05); which
it was between equal (HI-HI) and unequal (HI-MI) retention (P<.05 for
both escape latency and traveled distance). In the visible and probe tests, there
were no significant differences for escape latency and traveled distance.Performances in Equal Retention Tests
Figures3(d) and 4(d), there were significant differences
between LI-LI and MI-MI groups with HI-HI group in escape latency and traveled
distance (P<.05 for both) during retention tests. But this difference
was not significant between LI-LI and MI-MI groups.


## 3.1. Training Period

### 3.1.1. Hidden Platform Trials
(Day 1 to 3 between Groups)

Figure1(a) shows the results of training in the three levels
of noise during training period and visible test. There were significant
differences  in escape latency at day 1 [
F
(2, 20) = 14.48, P<.05],
day 2 [F (2, 20) =  27.62, P<.05], and day 3 [F (2, 20) = 10.53, P<.05]  between three groups. These significant
differences in the escape latency were between LI group with HI group in day 1
(P = .00), day 2 (P<.05), and also day 3 (P<.05).Effects of various
intensities of noise during training period on escape latency in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between different
intensities and LI.
(a)(b)For traveled distance, there were significant differences at
day 1 [F (2, 20) =  22.43, P<.05], day 2 [F (2, 20) =
83.7, P<.05], and day 3 [F (2, 20) = 19.44, P<.05]  between groups. At day 1 (Figure 2(a)), there were significant differences
between LI group with MI group (P<.05) and also HI group (P<.05).
At day 2 and 3, it showed a significant difference between LI group with HI
group (P<.05).Effects of various
intensities of noise during training period on traveled distance in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between
different intensities and LI.
(a)(b)Experiment 1: Performances in Exposure of Li Noise during Training Period, Equal and Unequal Retention Tests
There were no significant
differences between the results of day 1 to 3 in LI noise (Figures1(b) and 2(b)).
Figures 3(a) and 4(b) show there were significant
differences between equal and unequal retention tests (for escape latency F (2, 20) =14.1, P<.05 and also for traveled distance,
F  (2, 20) = 16.7, P<.05); it was between equal (LI-LI) and
unequal (LI-HI) retention tests (P<.05 for both escape latency and traveled
distance). In the visible and probe tests, there were no significant
differences for escape latency and traveled distance.Different effects of
noise exposure on escape latency. (a) Equal (LI-LI) and unequal, moderate (LI-MI)
and high (LI-HI) intensities, and retention tests in LI training group; (b) equal
(MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group;  (d) equal retention tests for LI, MI, and HI
training groups.*P<.05 shows a significant difference between
different intensities with equal group in a to c and LI group in d.
(a)(b)(c)(d)Different effects of
noise exposure on traveled distance. (a) Equal (LI-LI) and unequal, moderate
(LI-MI) and high (LI-HI) intensities, and retention tests in LI training group;
(b) equal (MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group; (d) equal
retention tests for LI, MI, and HI training groups.*P<0.05 shows a
significant difference between different intensities with equal group in a to c
and LI group in d.
(a)(b)(c)(d)Experiment 2: Performances in Exposure of Mi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed MI noise (Figures1(b) and 2(b)).
Figures 3(b) and 4(b) show there were significant differences between equal and
unequal retention tests (for escape latency, F  (2, 20)  = 17.3, P<.05
and for traveled distance, F (2, 20) = 18.7, P<.05); which
it was between equal (MI-MI) and unequal (MI-LI) retention tests (P<.05
for both escape latency and traveled distance). In the visible and probe tests,
there were no significant differences for escape latency and traveled distance.Experiment 3: Performances in Exposure of Hi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed HI noise (Figures1(b) and 2(b)).
Figures 3(c) and 4(c) show there were significant differences between equal and
unequal retention tests (for escape latency, F (2, 20) = 22.7, P<.05,
and for traveled distance, F (2,20) = 23.08, P<.05); which
it was between equal (HI-HI) and unequal (HI-MI) retention (P<.05 for
both escape latency and traveled distance). In the visible and probe tests, there
were no significant differences for escape latency and traveled distance.Performances in Equal Retention Tests
Figures3(d) and 4(d), there were significant differences
between LI-LI and MI-MI groups with HI-HI group in escape latency and traveled
distance (P<.05 for both) during retention tests. But this difference
was not significant between LI-LI and MI-MI groups.


## 3.1.1. Hidden Platform Trials
(Day 1 to 3 between Groups)

Figure1(a) shows the results of training in the three levels
of noise during training period and visible test. There were significant
differences  in escape latency at day 1 [
F
(2, 20) = 14.48, P<.05],
day 2 [F (2, 20) =  27.62, P<.05], and day 3 [F (2, 20) = 10.53, P<.05]  between three groups. These significant
differences in the escape latency were between LI group with HI group in day 1
(P = .00), day 2 (P<.05), and also day 3 (P<.05).Effects of various
intensities of noise during training period on escape latency in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between different
intensities and LI.
(a)(b)For traveled distance, there were significant differences at
day 1 [F (2, 20) =  22.43, P<.05], day 2 [F (2, 20) =
83.7, P<.05], and day 3 [F (2, 20) = 19.44, P<.05]  between groups. At day 1 (Figure 2(a)), there were significant differences
between LI group with MI group (P<.05) and also HI group (P<.05).
At day 2 and 3, it showed a significant difference between LI group with HI
group (P<.05).Effects of various
intensities of noise during training period on traveled distance in day 1–3 and visible
test (day 4).*P<.05 shows a significant difference between
different intensities and LI.
(a)(b)Experiment 1: Performances in Exposure of Li Noise during Training Period, Equal and Unequal Retention Tests
There were no significant
differences between the results of day 1 to 3 in LI noise (Figures1(b) and 2(b)).
Figures 3(a) and 4(b) show there were significant
differences between equal and unequal retention tests (for escape latency F (2, 20) =14.1, P<.05 and also for traveled distance,
F  (2, 20) = 16.7, P<.05); it was between equal (LI-LI) and
unequal (LI-HI) retention tests (P<.05 for both escape latency and traveled
distance). In the visible and probe tests, there were no significant
differences for escape latency and traveled distance.Different effects of
noise exposure on escape latency. (a) Equal (LI-LI) and unequal, moderate (LI-MI)
and high (LI-HI) intensities, and retention tests in LI training group; (b) equal
(MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group;  (d) equal retention tests for LI, MI, and HI
training groups.*P<.05 shows a significant difference between
different intensities with equal group in a to c and LI group in d.
(a)(b)(c)(d)Different effects of
noise exposure on traveled distance. (a) Equal (LI-LI) and unequal, moderate
(LI-MI) and high (LI-HI) intensities, and retention tests in LI training group;
(b) equal (MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group; (d) equal
retention tests for LI, MI, and HI training groups.*P<0.05 shows a
significant difference between different intensities with equal group in a to c
and LI group in d.
(a)(b)(c)(d)Experiment 2: Performances in Exposure of Mi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed MI noise (Figures1(b) and 2(b)).
Figures 3(b) and 4(b) show there were significant differences between equal and
unequal retention tests (for escape latency, F  (2, 20)  = 17.3, P<.05
and for traveled distance, F (2, 20) = 18.7, P<.05); which
it was between equal (MI-MI) and unequal (MI-LI) retention tests (P<.05
for both escape latency and traveled distance). In the visible and probe tests,
there were no significant differences for escape latency and traveled distance.Experiment 3: Performances in Exposure of Hi Noise during Training Period, Equal and Unequal Retention Tests
There were significant differences between the results of
day 1 to 3 in exposed HI noise (Figures1(b) and 2(b)).
Figures 3(c) and 4(c) show there were significant differences between equal and
unequal retention tests (for escape latency, F (2, 20) = 22.7, P<.05,
and for traveled distance, F (2,20) = 23.08, P<.05); which
it was between equal (HI-HI) and unequal (HI-MI) retention (P<.05 for
both escape latency and traveled distance). In the visible and probe tests, there
were no significant differences for escape latency and traveled distance.Performances in Equal Retention Tests
Figures3(d) and 4(d), there were significant differences
between LI-LI and MI-MI groups with HI-HI group in escape latency and traveled
distance (P<.05 for both) during retention tests. But this difference
was not significant between LI-LI and MI-MI groups.


## 4. Discussion

In this study, adult male rats
treated with different intensities of exposed noise displayed memory performance
impairments by increase in intensity of noise (47, 64, and 86 dbA). In training
period, it was significant difference between performance of groups in day 1
and day 2. Also this difference was shown in days 2 and 3 between HI with MI
and LI in escape latency and traveled distance. The longest time and traveled distance
to find the platform during acquisition period was seen at HI group. It is possible
that learning process might be impaired by high-intensity noise [22].
Also it showed that the time and distance to find the platform was improved
according to progression in training period, caused by learning process. In
visible test, there was no significant difference between LI and HI. This
finding is similar to Hamberick–Dixon's [13]
interpretation that they did not find different effects of noisy and quiet day
care center in separation of relevant visual cues, because of directing the
subjects to pay more attention to visual rather than auditory resources
[13, 23].
Also this is in agreement with
Glass and Singer's [16] findings that found the psychological and behavioral
adaptation to brief noise exposure. Also, this is in contrast with Broadbent
[3] finding which revealed the psychomotor task impaired by brief experimentally
imposed noise. Our results in experiment 2 support this
notion that a moderate-intensity noise (MI) in training period can promote
retention in high-intensity noise (MI-HI) than retention in low-intensity noise
(MI-LI). Several possible underlying explanations may explain this finding. Maes
& De Groot [5] have described that discrimination performance at under
noise situation is better than under silence situation supported with Zeng et al.
[4] findings. So we suggest that this promotion in performance at this
intensity might be associated with elevation of the arousal to an appropriate
level [24]. So silent conditions (LI in this
experiment) may be associated with under-arousal so that noise may elevate
arousal to a more optimal level; thereby increasing task performance [24]. Another suggestion of this
improvement is about adaptation with moderate levels so that rats can have an
appropriate attention and good performance
[6, 13, 25, 26].The present results in
experiment 3 showed that retention test in equal situation after exposure to
high-intensity noise (HI-HI) in training period caused less latency and traveled
distance rather than unequal retention in moderate noise (HI-MI). This finding
supports the “test-training context law” described that retention can
be better in equal contexts [27]. Also this is similar to this hypothesis
that the identical retention test of noise levels consequences has better
performance than do dissimilar noise levels [25]. The best time
and distance showed in retention tests of unequal low-intensity noise that
supports with external investigations [3, 5, 13, 20]. From our data, it could
be reasonable that the learning process might get disruption with high-intensity
noise [2, 22, 25]. Another possible
explanation of this disruption is that high-intensity noise may result in over-arousal that can
produce“panic effect” and also
disturbs attention
[5, 8, 17, 18, 21, 24, 26, 28].In experiment 4, it did not
show significant difference between LI-LI and MI-MI groups in equal retention
test. It may be associated with “power of training law” [2, 27] or it associated with the possibility of interaction
between the noise condition during training and retrieval of information [5]. But in unequal retention at high-intensity imposed
noise, it presented the big difference in the results as it has been reported
the role of high-intensity noise in memory processes [1, 5, 8, 10, 12–15, 21, 26]. We did not find significant
difference between speeds of these groups. It could be resulted that the motor
system of rats did not influence by noise.In general, it seems that the
interaction between training period and noise intensity might interfere with the
level of performance in special retention test. We concluded that when a group
trains at the special noise intensity in training period, it will get
adaptation with the situation, and then it will have lower performance in other
intensities at the retention tests, even at the lower intensities. So, it might
be better to train at the equal noise intensity, maybe adapt with this external
disruptive operant and decrease its influences.



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*Source: 840620-2009-02-16.xml*