Effect of the Orientation Difference on Components of Visual Event-Related Potentials
Changes in the components of visual event-related potentials (VERPs) depending on the difficulty of the identification counting tasks (“coarse” and “fine”) were studied in healthy humans. The basic finding is that much greater changes in the VERPs waves were observed within a 5 to 15 deg range th...
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Dushanova, J. Mitov, D. 2019-02-16T21:17:40Z 2019-02-16T21:17:40Z 2013 Effect of the Orientation Difference on Components of Visual Event-Related Potentials / J. Dushanova, D. Mitov // Нейрофизиология. — 2013. — Т. 45, № 3. — С. 273-278. — Бібліогр.: 20 назв. — англ. 0028-2561 https://nasplib.isofts.kiev.ua/handle/123456789/148099 612.821:612.822 Changes in the components of visual event-related potentials (VERPs) depending on the difficulty of the identification counting tasks (“coarse” and “fine”) were studied in healthy humans. The basic finding is that much greater changes in the VERPs waves were observed within a 5 to 15 deg range than those within the range of 15 to 90 deg. The amplitude of the second sensory component (P2), the latencies of both sensory components, and that of the second cognitive one increased with increase in the task difficulty, while the amplitudes of both cognitive components N2/P3 decreased. Additionally, small changes in the task difficulty affected the attentional effort and modulated the N1 amplitude and P2 latency. These VERP changes are considered an electrophysiological correlate of the psychophysical data when the “label” of an activated orientation-selective channel is sufficient for “coarse” discrimination, and an additional computational process comparing the responses of the activated channels makes discrimination possible in “fine” discrimination. У здорових суб’єктів досліджувалися зміни компонентів візуальних пов’язаних із подією потенціалів (ВППП), залежні від труднощів ідентифікації в завданнях із підрахунком (“грубим” або “тонким”). Основним спостереженням було наступне: в діапазоні 5–15 град відмічалися набагато більші зміни хвиль ВППП порівняно з такими в діапазоні 15–90 град. Амплітуда другого сенсорного компонента (P2), латентні періоди обох сенсорних компонентів і даний параметр другого когнітивного компонента зростали із збільшенням складності завдання, тоді як амплітуди обох когнітивних компонентів N2/P3 зменшувалися. Крім того, невеликі зміни складності завдання впливали на концентрацію уваги і модулювали амплітуду N1 та латентний період P2. Такі зміни ВППП розглядаються як електрографічні кореляти психофізіологічних даних, згідно з якими „мітка” активованого орієнтаційно селективного каналу є достатньою для „грубої” дискримінації, а додатковий процес розрахунків, забезпечуючий порівняння відповідей активованих каналів, робить можливою „тонку” дискримінацію. The authors acknowledge support from the National Science Fund (NSF) of Bulgaria (project 0475/2008). en Інститут фізіології ім. О.О. Богомольця НАН України Нейрофизиология Effect of the Orientation Difference on Components of Visual Event-Related Potentials Вплив відмінностей орієнтації на компоненти зорових пов’язаних із подією потенціалів Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials |
| spellingShingle |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials Dushanova, J. Mitov, D. |
| title_short |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials |
| title_full |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials |
| title_fullStr |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials |
| title_full_unstemmed |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials |
| title_sort |
effect of the orientation difference on components of visual event-related potentials |
| author |
Dushanova, J. Mitov, D. |
| author_facet |
Dushanova, J. Mitov, D. |
| publishDate |
2013 |
| language |
English |
| container_title |
Нейрофизиология |
| publisher |
Інститут фізіології ім. О.О. Богомольця НАН України |
| format |
Article |
| title_alt |
Вплив відмінностей орієнтації на компоненти зорових пов’язаних із подією потенціалів |
| description |
Changes in the components of visual event-related potentials (VERPs) depending on the
difficulty of the identification counting tasks (“coarse” and “fine”) were studied in healthy
humans. The basic finding is that much greater changes in the VERPs waves were observed
within a 5 to 15 deg range than those within the range of 15 to 90 deg. The amplitude of the
second sensory component (P2), the latencies of both sensory components, and that of the
second cognitive one increased with increase in the task difficulty, while the amplitudes of
both cognitive components N2/P3 decreased. Additionally, small changes in the task difficulty
affected the attentional effort and modulated the N1 amplitude and P2 latency. These VERP
changes are considered an electrophysiological correlate of the psychophysical data when the
“label” of an activated orientation-selective channel is sufficient for “coarse” discrimination,
and an additional computational process comparing the responses of the activated channels
makes discrimination possible in “fine” discrimination.
У здорових суб’єктів досліджувалися зміни компонентів
візуальних пов’язаних із подією потенціалів (ВППП), залежні від труднощів ідентифікації в завданнях із підрахунком (“грубим” або “тонким”). Основним спостереженням
було наступне: в діапазоні 5–15 град відмічалися набагато більші зміни хвиль ВППП порівняно з такими в діапазоні 15–90 град. Амплітуда другого сенсорного компонента
(P2), латентні періоди обох сенсорних компонентів і даний параметр другого когнітивного компонента зростали із
збільшенням складності завдання, тоді як амплітуди обох
когнітивних компонентів N2/P3 зменшувалися. Крім того,
невеликі зміни складності завдання впливали на концентрацію уваги і модулювали амплітуду N1 та латентний період
P2. Такі зміни ВППП розглядаються як електрографічні кореляти психофізіологічних даних, згідно з якими „мітка” активованого орієнтаційно селективного каналу є достатньою
для „грубої” дискримінації, а додатковий процес розрахунків, забезпечуючий порівняння відповідей активованих каналів, робить можливою „тонку” дискримінацію.
|
| issn |
0028-2561 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/148099 |
| citation_txt |
Effect of the Orientation Difference on Components of Visual Event-Related Potentials / J. Dushanova, D. Mitov // Нейрофизиология. — 2013. — Т. 45, № 3. — С. 273-278. — Бібліогр.: 20 назв. — англ. |
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| first_indexed |
2025-11-25T14:36:44Z |
| last_indexed |
2025-11-25T14:36:44Z |
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| fulltext |
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3 273
UDC 612.821:612.822
J. DUSHANOVA1 and D. MITOV1
EFFECT OF THE ORIENTATION DIFFERENCE ON COMPONENTS OF VISUAL
EVENT-RELATED POTENTIALS
Received November 11, 2012.
Changes in the components of visual event-related potentials (VERPs) depending on the
difficulty of the identification counting tasks (“coarse” and “fine”) were studied in healthy
humans. The basic finding is that much greater changes in the VERPs waves were observed
within a 5 to 15 deg range than those within the range of 15 to 90 deg. The amplitude of the
second sensory component (P2), the latencies of both sensory components, and that of the
second cognitive one increased with increase in the task difficulty, while the amplitudes of
both cognitive components N2/P3 decreased. Additionally, small changes in the task difficulty
affected the attentional effort and modulated the N1 amplitude and P2 latency. These VERP
changes are considered an electrophysiological correlate of the psychophysical data when the
“label” of an activated orientation-selective channel is sufficient for “coarse” discrimination,
and an additional computational process comparing the responses of the activated channels
makes discrimination possible in “fine” discrimination.
Keywords: sinusoidal gratings, orientation identification, visual ERPs (VERPs), sensory-
mental task.
1Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Correspondence should be addressed to J. Dushanova
(e-mail:juliana@bio.bas.bg).
INTRODUCTION
In a number of reports, the factors influencing
visual event-related potential (VERP) components
N1, P2, N2, and P3 were pointed out. One of these
factors for the N1 component is the type of the task,
namely detection or identification [1, 2]. The N1
discrimination effect is observed even when no motor
response is required, and this effect is present for both
color and form discriminations [2]. Moreover, this
discrimination-related effect is equally large for easy
and difficult discrimination tasks. The effect is not
proportional to the degree of the perceptual load. The
P2 VERP component is also differentially affected
by task demands. As is known, P2 requires selective
attention to different features, with the topographic
prevalence over a central line in the orientation and
location tasks extending further to the posterior side
than the response elicited under color discrimination
conditions [1]. Two selective stages, early selection in
high-load tasks and late selection in low-load tasks,
determine which stimulus is included in or excluded
from the attentional focus [3]. The P2 attention effect
is modulated by voluntary attentional allocation
between competing conditions [4, 5]. The P2 wave
can also be influenced by variations in the perceptual
loading. More precisely, the effect of P2 modulation
is termed N2 (in particular, its N2pc subcomponent),
which has been defined as a negative deflection in the
P2 component and is typically inspected at posterior
scalp sites. The N2pc wave is considered a response to
focusing attention on the features of a target stimulus
(like color) and ignoring distracters [1]. The nature
of the P3 wave is affected by the appearance of
unexpected task-irrelevant stimuli within an attended
stimulus train, the target probability [5], as well as
the degree of effort devoted by the subject to the
task [6]. It is important for practical applications to
look for electrophysiological evidence in support of
“coarse”/“fine” identification in the visual system.
In our study, we examined the effect of orientation
difference of sinusoidal gratings on the amplitude
and latency of VERP waves in mental tasks, such as
counting (i.e., with causing a substantial cognitive
load). The occurrence of the mental task should
produce additive effects on the wave components,
differing from binary motor conditions when
orientation difference was changed within the ranges
5 to 15 deg or 15 to 90 deg.
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3274
J. DUSHANOVA and D. MITOV
METHODS
Observers. The observers (11 women and 9 men,
31 ± 7 years) were with a normal or corrected-to-normal
visual acuity. They had no known ophthalmological or
neurological diseases. The subjects were instructed to
visually fixate the center of the screen. The handedness
was assessed by a questionnaire adapted from the
Edinburgh Handedness Inventory (Oldfield, 1971).
Stimuli. Stimuli were sinusoidal gratings with a
spatial frequency of 2.9 deg–1, presented in a circular
Gaussian window with the spatial constant of 0.483 deg
and contrast of 0.05. They were presented for 100 msec
in the center of the visual field. Stimulus orientation
was 90, 85, 75, or 0 deg.
Apparatus. The stimuli were generated by a
computer as 12-bit signals and were displayed on the
screen of a monochrome monitor (640 × 480 pixels,
frame rate 60 Hz). The viewing distance was 1.14 m,
and the mean luminance was 50 cd/m2; it was not
changed by stimulus onset and offset.
Procedure. In each trial, the stimulus orientation
varied randomly between two possible values – 90
and 0 deg, 90 and 75 deg, as well as 90 and 85 deg.
Therefore, the difference between orientations was
90, 15, and 5 deg. The subjects performed a sensory-
mental task. They had to count the number of stimuli
with orientation different from vertical (90 deg) when
the stimulus had an oblique or a horizontal orientation.
The interval between trials varied randomly within
the range of 2.5 to 3.5 sec. Each block contained
100 trials. The EEG was recorded from 12 leads, Fz,
Cz, Pz, Oz, C3, C4, T3, T4, P3, P4, O1, and O2 (10/20
system), with reference to both processi mastoidei
and a ground electrode placed on the forehead. The
oculogram (EOG) was recorded via electrodes placed
above and below the lateral cantus of the left eye (for
detection of eye movements and blink artifacts). EEG
and EOG data were recorded using a Nihon Kohden
EEG-4314F (Japan; cut-off frequencies 0.3 and 70 Hz)
together with markers of the stimulus onset, as well as
those of motor responses. The signals were digitized at
a rate of 500 sec–1 and recorded on a hard disk for off-
line analysis. The length of EEG segments was chosen
to cover 500-msec pre-stimulus and 1,000-msec post-
stimulus intervals. Only artifact-free VERP records
were processed. Extraction of the baseline correction
corresponded to the 300-msec-long pre-stimulus time
period (i.e., –400 to –100 msec). The parameters of
VERP waves were computed relatively to the corrected
baseline. Later on, the signals were verified to have
a signal-to-noise ratio (SNR) above mean 1.1. The
SNRs were calculated using the following formula:
SNR = A/2 · s.d.noise, where the amplitude A is the
peak-to-peak voltage of the mean VERP, and s.d.noise
is the noise standard deviation [7]. The noise ε was
obtained by subtracting the mean from each individual
VERP. In other words, for a given single electrode,
ε is just the collection of residuals when the mean
ERP is subtracted from each individual VERP, and
s.d.noise is the standard deviation over this collection.
The mean interval across stimulus/task combination
for each wave was N1 (80 and 140 msec), P2 (130
and 200 msec), N2 (190 and 298 msec), and P3 (290
and 550 msec). The statistical differences between
the corresponding VERP components at orientation
differences 90/15, 90/5, and 15/5 deg were obtained by
means of the Kruskal–Wallis test for paired comparison
of the scalp leads between stimulus datasets.
RESULTS
Performance Accuracy. The performance accuracy
of the counting at the smallest orientation difference
5 deg was the worse (mean ± s.e.m., 91.12 ± 2.03%)
in comparison with the accuracy at the medium 15 deg
(96.97 ± 0.76%) and the highest 90 deg (95.76 ±
± 2.10%) orientation difference. Pair comparison of the
performance accuracy observed at different orientation
differences showed the following results: F(5 deg and 15 deg)
(1, 39) = 5.09, P(5 deg and 15 deg) = 0.024; F(5 deg and 90 deg)
(1, 39) = 6.72, P(5 deg and 90 deg) = 0.0095, F(15 deg and 90 deg)
(1, 39) = 0.35, P(15 deg and 90 deg) = 0.55.
Orientation Difference-Related Effect on the
VERP Waves. The first negative VERP wave N1
showed an amplitude scalp distribution with a maximal
value at the temporal lobe and a minimal value at the
occipital lobe. This was observed at the orientation
differences of 90 and 5 deg (Fig. 1A, first row), as
at the medium orientation difference (15 deg). The
maximal values of N1 were observed over the central
scalp positions (Fig. 1A, first row).
The amplitude of the N1 component first increased
with decrease in the orientation difference from 90
to 15 deg and then decreased with further decrease in
the above difference. This was not in the case at two
scalp positions, T3 and T4, where the amplitude of
the N1 component did not depend on the orientation
difference. The latency of the N1 component (Fig. 1B,
first row) did not demonstrate clear extremes at any
scalp positions, as it became longer with decrease in
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3 275
EFFECT OF THE ORIENTATION DIFFERENCE ON COMPONENTS OF VISUAL ERPs
–9
–9
–10
–10
–11
–8
–8
µV
1
2
3
BA
b
a
c
d
–7
–7
–6
–6
–5
–5
–4
–4
3
2
100
160
1
90
150
140
4
110
1705
6
120
180
7
8
130
msec
190
9
8
Fz FzCz CzPz PzC3 C3C4 C4P3 P3P4 P4O1 O1O2 O2Oz OzT3 T3T4 T4
10
11
12
13
14
220
420
200
400
380
240
260
440
280
460
F i g. 1. Scalp distributions and statistical comparisons of the amplitudes of visual event-related potential (VERP) waves (N1, P2, N2,
and P3, a-d, respectively). A and B) Amplitudes (mV) and latencies (msec) of VERP components recorded at three orientation differences
(curves 1-3 correspond to 90, 15, and 5 deg, respectively). All parameters of the VERP components presented on this figure are those of
the responses to vertical gratings only. Vertical bars represent 95% confidence intervals. Circles, squares, and asterisks indicate results
of different pair comparisons: 5 deg difference with that of 15 deg (circles), 5 deg difference with that of 90 deg (squares), and 15 deg
difference with that of 90 deg (asterisks). The colors of these symbols correspond to different critical values of the significance: black,
P < 0.001, gray, P < 0.01, and light gray, P < 0.05. Horizontal scale) Scalp leads according to the 10/20 international system.
Р и с. 1. Топографічний розподіл та статистичні порівняння амплітуд хвиль візуальних пов’язаних з подією потенціалів (N1, P2,
N2 та P3, a–d відповідно).
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3276
J. DUSHANOVA and D. MITOV
the orientation differences. However, the prolongation
of the N1 latency was statistically significant within
the orientation difference range of 5 to 15 deg only at
most electrode positions, with the exceptions at O1
and Oz, where the orientation difference influenced
the N1 latency within all the values studied (5 to
90 deg).
The P2 wave demonstrated the maximal amplitude
over the fronto-central and sensorimotor areas
at all orientation differences. The maximal P2
amplitude was also observed over the temporal
area at the greatest (90 deg) and the smallest
(5 deg) orientation differences. The minimal values
of the P2 amplitude were observed over the occipital
and parietal areas, as well as over the temporal
area, at the medium orientation difference (15 deg;
Fig. 1A, second row, black and gray). The amplitude
of the P2 component increased with decrease in the
orientation difference, as this effect was statistically
significant in the frontal areas within the range of
5 to 15 deg only; there are no asterisks in Fig. 1B,
second row, with the exception at T4 only, which
indicates statistically significant changes caused by
the orientation difference variation within the range of
90 to 15 deg. Similarly to the amplitude distribution,
the P2 latency also demonstrated maximal values over
the fronto-central, sensorimotor, and temporal areas,
and minimal values were observed over the occipital
lobe (Fig. 1B, second row). The P2 latency first
decreased with decrease in the orientation difference
from 90 to 15 deg and then increased with further
decrease in this difference. Changes in the P2 latency
were statistically significant within the entire range of
orientation differences studied (5 to 90 deg) at most
scalp positions, with exceptions at P3 and O1 leads,
where changes in the P2 latency were observed within
the 5 to 15 deg range.
The N2 wave showed a maximal amplitude over
the occipital lobe and a minimal amplitude over the
central fronto-parietal, sensorimotor, and temporal
cortex areas. This was better expressed at the greatest
(90 deg) and the medium (15 deg) orientation
differences, and, to a lesser extent, at the smallest
(5 deg) difference (Fig. 1A, third row). The N2
amplitude decreased with decrease in the orientation
difference, mainly within the range of 5 to 15 deg.
This effect, however, was not observed in the temporal
lobe, where the N2 amplitude was not influenced
by the orientation difference. The latency of the N2
component demonstrated maximal values over the
fronto-central, sensorimotor, and temporal areas,
and a minimal value over the occipital lobe. The N2
latency became longer with decrease in the orientation
difference, but this effect was statistically significant
only within the 5 to 15 deg range, with two exceptions
(C3 and T4) where the effect of the orientation
difference was statistically significant within the
entire studied range, 5 to 90 deg (Fig. 1B, third row).
The amplitude scalp distribution of the P3 wave
demonstrated a maximum in the central frontal areas
(Fz and Cz) for all three orientation differences
(Fig. 1A, fourth row). The P3 amplitude increased as
the orientation difference increased, and this increase
was statistically significant within the range of 5 to
15 deg for scalp positions Cz, Pz, P3, O1, Oz, and
T4 and within the range of 15 to 90 deg for position
T4. The P3 latency demonstrated a small maximum
at frontal leads, and this effect was more evident at
smallest orientation differences. The latency of the P3
component lengthened with decrease in the orientation
difference within the entire range of orientation
difference variation (5 to 90 deg; Fig. 1B, fourth row).
DISCUSSION
An increase in task difficulty (decrease in the
orientation difference from 15 to 5 deg) resulted in
the reduction of the N1 amplitude in VERPs recorded
in the sensory-mental task. At the same time, the N1
amplitude increased with decrease in the orientation
difference within the range of 90 to 15 deg [7]. It might
be suggested that counting is a process generating
a different type of brain activity that interferes with
activity involved in an identification process. The
fact that the oblique grating could not be adequately
identified and counted at a small orientation difference
suggests that the insufficient discrimination resulted
from either exhaustion of the perceptual or cognitive
capacity (which gives the ability to count accurately)
or the attention that can be set to block irrelevant
inputs from selected processing. The effect of task
difficulty can be considered an effect of attentional
effort modulation [8-10]. Modulation of the attentional
effort related to transition of the orientation difference
(15 deg) between easy (90 deg) and difficult (5 deg)
orientation tasks can be explained by the assumption
that the first sensory component corresponds to more
than one active attentional process, such as an “N1
discrimination effect” and an “N1 reorienting effect”
[11]. The former N1 attention effect may involve a
discriminative process restricted to an oriented area
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3 277
EFFECT OF THE ORIENTATION DIFFERENCE ON COMPONENTS OF VISUAL ERPs
in the sensory space and may reflect an enhanced
perceptual processing [11]. The N1 “reorienting
effect” represents an enhanced negativity reflecting an
attentional switch from one orientation to another [4].
The N1 discrimination effect can only be influenced
by mental fatigue that decreases attention [12]. An
increase in task difficulty prolongs the latency of the
N1 wave because the process of counting includes an
increased level of difficulty when a subject estimates
the number of stimuli with small orientations, keeps
track of the running sum, and retrieves and generates
the count-words. In addition, demands are executive
processes in both memory and attention (to keep track
of which gratings have already been counted and ensure
the process of continuing in an effective way over
time). This provides evidence for a more generalized
change in the attentional modulation and interaction
of selective attention with working memory.
The next VERP wave P2 demonstrated changes in
the amplitude predominantly within the orientation
difference range of 5 to 15 deg. The amplitude of the
P2 wave increased with decrease in the orientation
difference. With respect to the anterior P2 waves,
it was found that their amplitude increased with
increase in task difficulty within the 5-15 deg range.
Similarly to the case of the N1 amplitude, the task
difficulty within the 15-5 deg orientation difference
prolonged the P2 latency, while it reduced this latency
within the orientation difference range of 90-15 deg
because small changes in the task difficulty affected
the attentional effort and modulated the parameters
of the P2/N1 complex [9, 10]. Visual attention has
been found to be an effort-extensive process, which
depends on the nature of the task [3-5]. Components
like P2/N1 have demonstrated modulation due to
attending to features like orientation or color and can
actually contribute to the measurement of cognitive
processes in the visual system [1, 10]. The differences
in the direction of the P2 effect found in studies with
different types of task may indicate that the P2 reflects
activation of different visual pathways, namely the
pathway processing target- and direction-related
information and the pathway processing information
about the movement.
The amplitude of the next negative VERP wave, N2,
decreased with decrease in the orientation difference.
Similarly to the influence of the task on the N1
latency, an increase in the task difficulty resulted
in prolongation of the N2 latency. The anterior N2
component is sensitive to orientation discrimination
in both sensory/mental and motor experiments [7].
The posterior N2 amplitude was much more prominent
than that of the anterior N2 in the counting task. The
maximal amplitude was observed in the occipital sites
for easy discrimination. These posterior N2 differences
elicited were influenced by both the experimental
context and the effect of the target status, as arising
from deviation in the task difficulty. The majority
of observed N2-related effects could be attributed to
some processes, such as response inhibition, response
conflict, and error monitoring [13]. The instructions
requested only accuracy in silent counting. The
N2 component included also a related activity in
unsuccessful trials. The error-related negativity may
reflect the adjustment of short- and long-term response
strategies after a mistake, a compensatory response,
and a slower response in the subsequent trial [13].
The amplitude of the endogenous (ERP) P3
wave decreased with increase in the task difficulty.
Correlations between decrease in the orientation
difference and the amplitude in a cover-response
task were consistent with the viewpoint that more
difficult tasks are associated with less attention to the
targets [10, 14]. The flexible strategies of distributing
attention were evidently no longer available, and
the P3 wave was rather a measure of allocation of
attentional resources in the sensory-mental study
[15]. When subjects performed the counting task,
additional demands are imposed on both memory and
executive processes (to keep track of which gratings
have already been counted and ensure the process
of continuing in an effective way over time). The
insufficient discrimination resulted from exhaustion
of either perceptual/cognitive capacity or the attention
and selected processing. Therefore, the attentional
fatigue reflected a reduction of the P3 amplitude with
increase in the task difficulty. The latency of the P3
component is believed to correspond to the rate of
cognitive processing [13]. The P3 latency increased
with decrease in the orientation difference in counting
tasks. This was associated with the task difficulty
and looked like a measure of the duration of stimulus
evaluation processes (encoding, recognition, and
classification) independent of response selection and
execution [16, 17].
The basic result of our experiments is the fact that
much greater changes in the VERP waves are observed
within the range of 5 to 15 deg than those within the
range of 15 to 90 deg. Small changes in the attentional
effort can, however, also modulate the parameters of
some waves within the orientation difference from
15 to 90 deg in the transition zone between easy and
NEUROPHYSIOLOGY / НЕЙРОФИЗИОЛОГИЯ.—2013.—T. 45, № 3278
J. DUSHANOVA and D. MITOV
difficult tasks (orientation difference 15 deg) [9]. The
relationship between the response conflict and error
detection remains a contentious issue. In summary,
under conditions of our experiments, stimuli activated
either independent orientation-selective mechanisms
(at 15 and 90 deg orientation differences) or
mechanisms with overlapping tuning curves (at a 5 deg
orientation difference) [7, 18-20].
All experiments reported in this paper were carried out
under an approved protocol from the Ethics Committee of the
Institute of Neurobiology (BAS), and all subjects gave their
written informed consent according to the Helsinki declaration.
The authors, J. Dushanova and D. Mitov, declare that
they have no potential competing interests or commercial
relationship, including grants, honoraria, speaker’s lists,
significant ownership, and support from pharmaceutical or other
companies such as manufactures of equipment and diagnostic
or other laboratories whose products are directly or indirectly
involved or affected by the article.
The authors acknowledge support from the National Science
Fund (NSF) of Bulgaria (project 0475/2008).
Ю. Душанова1, Д. Мітов1
ВПЛИВ ВІДМІННОСТЕЙ ОРІЄНТАЦІЇ НА КОМПОНЕН-
ТИ ЗОРОВИХ ПОВ’ЯЗАНИХ ІЗ ПОДІЄЮ ПОТЕНЦІАЛІВ
1 Інститут нейробіології Болгарської Академії наук, Софія
(Болгарія).
Р е з ю м е
У здорових суб’єктів досліджувалися зміни компонентів
візуальних пов’язаних із подією потенціалів (ВППП), за-
лежні від труднощів ідентифікації в завданнях із підрахун-
ком (“грубим” або “тонким”). Основним спостереженням
було наступне: в діапазоні 5–15 град відмічалися набага-
то більші зміни хвиль ВППП порівняно з такими в діапа-
зоні 15–90 град. Амплітуда другого сенсорного компонента
(P2), латентні періоди обох сенсорних компонентів і да-
ний параметр другого когнітивного компонента зростали із
збільшенням складності завдання, тоді як амплітуди обох
когнітивних компонентів N2/P3 зменшувалися. Крім того,
невеликі зміни складності завдання впливали на концентра-
цію уваги і модулювали амплітуду N1 та латентний період
P2. Такі зміни ВППП розглядаються як електрографічні ко-
реляти психофізіологічних даних, згідно з якими „мітка” ак-
тивованого орієнтаційно селективного каналу є достатньою
для „грубої” дискримінації, а додатковий процес розрахун-
ків, забезпечуючий порівняння відповідей активованих ка-
налів, робить можливою „тонку” дискримінацію.
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