Andrey Nikolaev | KU Leuven (original) (raw)
Papers by Andrey Nikolaev
Attention, Perception & Psychophysics, 2019
We investigated visual working memory encoding across saccadic eye movements, focusing our analys... more We investigated visual working memory encoding across saccadic eye movements, focusing our analysis on refixation behavior. Over 10-s periods, participants performed a visual search for three, four, or five targets and remembered their orientations for a subsequent change-detection task. In 50% of the trials, one of the targets had its orientation changed. From the visual search period, we scored three types of refixations and applied measures for quantifying eye-fixation recurrence patterns. Repeated fixations on the same regions as well as repeated fixation patterns increased with memory load. Correct change detection was associated with more refixations on targets and less on distractors, with increased frequency of recurrence, and with longer intervals between refixations. The results are in accordance with the view that patterns of eye movement are an integral part of visual working memory representation.
Do we perceive a group of dancers moving in synchrony differently from a group of drones flying i... more Do we perceive a group of dancers moving in synchrony differently from a group of drones flying in-sync? The brain has dedicated networks for perception of coherent motion and interacting human bodies. However, it is unclear to what extent the underlying neural mechanisms overlap. Here we delineate these mechanisms by independently manipulating the degree of motion synchrony and the humanoid quality of multiple point-light displays (PLDs). Four PLDs moving within a group were changing contrast in cycles of fixed frequencies, which permits the identification of the neural processes that are tagged by these frequencies. In the frequency spectrum of the steady-state EEG we found two emergent frequency components, which signified distinct levels of interactions between PLDs. The first component was associated with motion synchrony, the second with the human quality of the moving items. These findings indicate that visual processing of synchronously moving dancers involves two distinct neural mechanisms: one for the perception of a group of items moving in synchrony and one for the perception of a group of moving items with human quality. We propose that these mechanisms underlie high-level perception of social interactions. Synchronous motion is frequently found in the animal kingdom: flocks of birds fly together in harmony, schools of fish swim in perfect unison, orcas hunt by navigating their motion in perfect synchrony. Humans are no exception. Synchrony might have been important in our evolution as a social species because it facilitates psychological unification in a cooperative society 1. Moreover, synchronous motion is used to create choreography, which we often find appealing. Who was not impressed by the perfectly in-sync performance in the opening ceremony of the Summer Olympics of 2008 in Beijing? Synchronous motion is also not particular to animate creatures. It is also applied to the movements of man-made things, such as multiple swings, flying drones, fireworks exploding together (see examples here: http://gestaltrevision.be/s/SynMotion). How does the brain process these synchronized motions? To what extent is the synchrony of human motions special as opposed to inanimate synchronous motions?. Until now, studies of neural mechanisms underlying motion perception focused mostly on low-level coherent motion, i.e., common fate 2,3. Another group of studies considered higher-level visual processing of biological motion 4–7. This line of studies was initiated in 1973 by Johansson, who has shown that only few point-lights attached to the joints of a human carrying out a specific action (e.g., walking, running, jumping) are sufficient for us to perceive a specific biological motion 8. Such point-light displays (PLDs) are capable to carry specific information about the biological nature of the motion without other cues, such as familiarity, shape and color 8. Therefore, PLDs have been used frequently to investigate perception of motion of single human figures 4–6. Later, multiple PLDs were used to study high-level perception of motion in a social context, including meaningful interactions between agents involved in reciprocal actions or reacting to each other 9–11. These studies revealed that detection
Int J Psychophysiol, 1997
Biological Psychology, 2008
Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Librar... more Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Libraries; Toledo; Intranet; KU Leuven Nederlands. logo zoekterm: Navigation. Education: International programmes; Faculties; ECTS; Vision and policy. Research: Research at KU Leuven; Support and funding; Industry and society; PhD; Postdoc researchers; Output and impact; Networking; Vision and policy. Admissions: How to apply; Scholarships; Degree-seeking students; ...
"Visual integration between target and irrelevant features leads to effects of irrelevant feature... more "Visual integration between target and irrelevant features leads to effects of irrelevant feature congruency (Stroop) or variation (Garner) on classification response performance. In a factorial design, Stroop and Garner effects were obtained on response times and error rates, and their correlates in brain activity were observed in event-related potentials (ERP). Stroop effects were manifested in ERP amplitude at the latencies of the N1 and N2 components, starting about 170 ms after stimulus onset. Garner effects were observed in the amplitude of the rising part of the P3 component, starting about 330 ms after stimulus onset. The difference in time course between Stroop and Garner effects is in accordance with the view that both are produced by different mechanisms, the former sensitive to interference within presentations and the latter to interference between presentations.
"
PERCEPTION- …, Jan 1, 2003
According to a widely cited finding by Ellis & Stark (1978), the duration of eye fixations is lon... more According to a widely cited finding by Ellis & Stark (1978), the duration of eye fixations is longer at the instant of perceptual reversal of an ambiguous figure than before or after the reversal. However, long fixations are more likely to include samples of an independent random event than short fixations. This sampling bias would produce the pattern of results also when no correlation exists between fixation duration and perceptual reversals. When an appropriate correction is applied to the measurement of fixation durations, the effect disappears. In fact there are fewer actual button presses during the long intervals than would be expected by chance. Moving window analyses performed on eye-fixation data reveal that no unique eye-event is associated with switching behavior. However, several indicators such as blink frequency, saccade frequency, and the direction of the saccade each are differentially sensitive to perceptual and response-related aspects of the switching process. The time course of these indicators depicts switching behavior as a process of cascaded stages.
AIP Conference Proceedings, 2004
Spatio-temporal dynamics of alpha activity during the resting state is characterized by alternati... more Spatio-temporal dynamics of alpha activity during the resting state is characterized by alternation between ordered and disordered states. The ordered state exhibits a variety of phase patterns. We found that the duration distributions of these states and phase patterns obey power laws. These results suggest that the appearance of phase patterns and the alternation between ordered and disordered states are not just due to noise but products of internal dynamics of the brain. We discuss the possibility that these dynamics are ...
ABSTRACT We tested the memory characteristics of visual search in an event-related potentials stu... more ABSTRACT We tested the memory characteristics of visual search in an event-related potentials study. Participants searched for a target letter presented among nontarget letters. We varied target identity (switch to new vs swap with nontarget from previous trial), nontarget identity (switch to new vs swap with target from previous trial), target location (repeat, switch, swap with nontarget), and nontarget location (repeat, switch, swap with target). Repeated target locations were responded to faster and more accurately than switched ones. There was a slowdown in performance when nontarget and target swapped their locations. The amplitude in the N2pc component was smaller when target location switched than repeated. The amplitude in the N1 component was highest when target and nontarget swapped their roles and target location switched; and smallest when both target and nontarget switched to new identity and target location repeated. These data show that visual search has memory for both target location and identity, but also nontarget identity and location play a role in processing.
Neuroreport, May 1, 2009
Selection of visual short-term memory content takes place during perceptual and postperceptual pr... more Selection of visual short-term memory content takes place during perceptual and postperceptual processing. We studied postperceptual selection in a change detection task, in which spatially distributed cues preceding the memory array marked potential change targets. In the 550-730 ms interval after the memory array onset but not in the following retention interval, event-related potentials showed larger contralateral delay activity when the spatial cues were selective than when they were unselective. This finding implies that distributed precueing strengthens the visual short-term memory representation during an extended memory consolidation phase. NeuroReport
Neuroscience and Behavioral Physiology, 1995
The stages of the mental rotation of complex three-dimensional figures were investigated in nine ... more The stages of the mental rotation of complex three-dimensional figures were investigated in nine healthy subjects using the intracortical interaction mapping technique. It was established that mental rotation is accomplished with the participation of both parietal regions; the prerotation setup is associated with the involvement of the frontal, central, and right temporal divisions of the brain; decision-making regarding the result of the rotation and the response is accomplished through the conjunction of both frontal and temporoparietooccipital regions of the left hemisphere. In the case of the unsuccessful solution of the problem the process seems to stop at the stage of the prerotation setup. With verbal control the configuration of the zone of high-level association during the first three stages is reminiscent of that observed in the baseline activity.
Physical Review E Statistical Nonlinear and Soft Matter Physics, Aug 1, 2007
We investigate patterns of collective phase synchronization in brain activity in awake, resting h... more We investigate patterns of collective phase synchronization in brain activity in awake, resting humans with eyes closed. The alpha range of human electroencephalographic activity is characterized by ever-changing patterns, with strong fluctuations in both time and overall level of phase synchronization. The correlations of these patterns are reflected in power-law scaling of these properties. We present evidence that the dynamics underlying this fluctuation is type-I intermittency. We present a model study illustrating that the scaling property and the collective intermittent dynamics are emergent features of globally coupled phase oscillators near the critical point of entering global frequency locking.
Journal of Cognitive Neuroscience, Dec 1, 2005
PloS one, 2016
Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain a... more Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent activity occurred in the delta, theta, alpha and beta bands of the signal in the form of large-scale waves, which propagated with a variety of velocities. Their mean speed at each frequency band was proportional to temporal frequency, giving a range of 0.06 to 4.0 m/s, from delta to beta. The wave peaks moved over the entire measurement array, during both ongoing activity and task-relevant intervals; direction of motion was more predictable during the latter. A large proportion of the cortical signal, measurable at the scalp, exists as large-scale coherent motion. We argue that the distribution of observable phase velocities in MEG is domina...
Perception Abstract, Feb 1, 2003
Page 1. Traveling Waves of Spontaneous Alpha EEG Activity phase synchronization method for spat... more Page 1. Traveling Waves of Spontaneous Alpha EEG Activity phase synchronization method for spatio-temporal EEG pattern analysis Junji Ito, Andrey R Nikolaev and Cees van Leeuwen Laboratory for Perceptual Dynamics ...
The aim of this study was to investigate an interaction between frontal and left temporo-parietal... more The aim of this study was to investigate an interaction between frontal and left temporo-parietal cortices in tasks requiring word association. A new method was used to examine averaged event-related potentials in different frequency bands by calculating correlation coef®cients between wavelet curves in distant cortical areas. This method was applied to previous event-related potentials recordings which found successive activation of frontal and left posterior areas . Correlated activity at 17 Hz was observed between frontal and left temporal (Wernicke's) areas prior to full activation of Wernicke's area. q
Zhurnal vysshei nervnoi deiatelnosti imeni I P Pavlova
Solution of spatial and verbal tasks was studied in 43 subjects using the advanced version of the... more Solution of spatial and verbal tasks was studied in 43 subjects using the advanced version of the method of intracortical interaction mapping (IIM) and analysis of EEG spectra in short (250 ms) intervals. Comparison between the IIM and coherence methods during solving simple motor tasks revealed some advantages of the IIM for studying of labile cortical connections. Several stages were separated in the process of solution of the mental task in accordance with patterns of cortical connections. The duration of the stages was similar in both kinds of tasks and corresponded to that revealed in psychological experiments. Cortical connections in the theta range were generalized and reflected the level of general tension. This unspecific tension was high for the whole period of the spatial task solution while in the verbal task the tension increased to the stage of decision making. Task-specific patterns were revealed in the beta range. The right parietal and temporal regions were the centers of EEG connections during solution of the spatial task while the left central area was essential for the verbal task solution. The left parietal area was involved in solution of both kinds of tasks. The frequency parameters of connections in the beta range were stable during the spatial task solving, and in the process of verbal task solving the dominant frequency changed after the initial (perception) stage probably due to switching to another thinking mechanism.
Zhurnal vysshei nervnoi deiatelnosti imeni I P Pavlova
The EEG spectral power in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) was studied durin... more The EEG spectral power in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) was studied during mental rotation of two- and three-dimensional objects. Only those EEG segments were analyzed which corresponded to the tasks with similar time of solving. The EEG spectral power of the alpha range was higher under control conditions than during task solving. The spectral power in the range of 15-45 Hz was higher under the operation than under the control conditions. This finding confirms the assumption that EEG desynchronization in the alpha range is accompanied by the high-frequency synchronization. The EEG high-frequency power was higher during mental rotation of two-dimensional objects than three-dimensional ones. Since the angular difference between the two-dimensional objects was larger than between the three-dimensional ones, the rotation angle rather than the "depth" of space increased cortical activation. Under experimental conditions, EEG spectral power in the range of 15-45 Hz was always the highest in the occipital areas, which was associated with the visual modality of stimuli. The EEG spectral power in the gamma range (35-45 Hz) was substantially higher at the first second of operation as compared with the second one testifying that EEG changes in this range are more related with the processes of perception and recognition than with mental operations with images.
Attention, Perception & Psychophysics, 2019
We investigated visual working memory encoding across saccadic eye movements, focusing our analys... more We investigated visual working memory encoding across saccadic eye movements, focusing our analysis on refixation behavior. Over 10-s periods, participants performed a visual search for three, four, or five targets and remembered their orientations for a subsequent change-detection task. In 50% of the trials, one of the targets had its orientation changed. From the visual search period, we scored three types of refixations and applied measures for quantifying eye-fixation recurrence patterns. Repeated fixations on the same regions as well as repeated fixation patterns increased with memory load. Correct change detection was associated with more refixations on targets and less on distractors, with increased frequency of recurrence, and with longer intervals between refixations. The results are in accordance with the view that patterns of eye movement are an integral part of visual working memory representation.
Do we perceive a group of dancers moving in synchrony differently from a group of drones flying i... more Do we perceive a group of dancers moving in synchrony differently from a group of drones flying in-sync? The brain has dedicated networks for perception of coherent motion and interacting human bodies. However, it is unclear to what extent the underlying neural mechanisms overlap. Here we delineate these mechanisms by independently manipulating the degree of motion synchrony and the humanoid quality of multiple point-light displays (PLDs). Four PLDs moving within a group were changing contrast in cycles of fixed frequencies, which permits the identification of the neural processes that are tagged by these frequencies. In the frequency spectrum of the steady-state EEG we found two emergent frequency components, which signified distinct levels of interactions between PLDs. The first component was associated with motion synchrony, the second with the human quality of the moving items. These findings indicate that visual processing of synchronously moving dancers involves two distinct neural mechanisms: one for the perception of a group of items moving in synchrony and one for the perception of a group of moving items with human quality. We propose that these mechanisms underlie high-level perception of social interactions. Synchronous motion is frequently found in the animal kingdom: flocks of birds fly together in harmony, schools of fish swim in perfect unison, orcas hunt by navigating their motion in perfect synchrony. Humans are no exception. Synchrony might have been important in our evolution as a social species because it facilitates psychological unification in a cooperative society 1. Moreover, synchronous motion is used to create choreography, which we often find appealing. Who was not impressed by the perfectly in-sync performance in the opening ceremony of the Summer Olympics of 2008 in Beijing? Synchronous motion is also not particular to animate creatures. It is also applied to the movements of man-made things, such as multiple swings, flying drones, fireworks exploding together (see examples here: http://gestaltrevision.be/s/SynMotion). How does the brain process these synchronized motions? To what extent is the synchrony of human motions special as opposed to inanimate synchronous motions?. Until now, studies of neural mechanisms underlying motion perception focused mostly on low-level coherent motion, i.e., common fate 2,3. Another group of studies considered higher-level visual processing of biological motion 4–7. This line of studies was initiated in 1973 by Johansson, who has shown that only few point-lights attached to the joints of a human carrying out a specific action (e.g., walking, running, jumping) are sufficient for us to perceive a specific biological motion 8. Such point-light displays (PLDs) are capable to carry specific information about the biological nature of the motion without other cues, such as familiarity, shape and color 8. Therefore, PLDs have been used frequently to investigate perception of motion of single human figures 4–6. Later, multiple PLDs were used to study high-level perception of motion in a social context, including meaningful interactions between agents involved in reciprocal actions or reacting to each other 9–11. These studies revealed that detection
Int J Psychophysiol, 1997
Biological Psychology, 2008
Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Librar... more Taakbalk. taskbar; subnavigation; contents. Contact; Who's who; Organisational chart; Libraries; Toledo; Intranet; KU Leuven Nederlands. logo zoekterm: Navigation. Education: International programmes; Faculties; ECTS; Vision and policy. Research: Research at KU Leuven; Support and funding; Industry and society; PhD; Postdoc researchers; Output and impact; Networking; Vision and policy. Admissions: How to apply; Scholarships; Degree-seeking students; ...
"Visual integration between target and irrelevant features leads to effects of irrelevant feature... more "Visual integration between target and irrelevant features leads to effects of irrelevant feature congruency (Stroop) or variation (Garner) on classification response performance. In a factorial design, Stroop and Garner effects were obtained on response times and error rates, and their correlates in brain activity were observed in event-related potentials (ERP). Stroop effects were manifested in ERP amplitude at the latencies of the N1 and N2 components, starting about 170 ms after stimulus onset. Garner effects were observed in the amplitude of the rising part of the P3 component, starting about 330 ms after stimulus onset. The difference in time course between Stroop and Garner effects is in accordance with the view that both are produced by different mechanisms, the former sensitive to interference within presentations and the latter to interference between presentations.
"
PERCEPTION- …, Jan 1, 2003
According to a widely cited finding by Ellis & Stark (1978), the duration of eye fixations is lon... more According to a widely cited finding by Ellis & Stark (1978), the duration of eye fixations is longer at the instant of perceptual reversal of an ambiguous figure than before or after the reversal. However, long fixations are more likely to include samples of an independent random event than short fixations. This sampling bias would produce the pattern of results also when no correlation exists between fixation duration and perceptual reversals. When an appropriate correction is applied to the measurement of fixation durations, the effect disappears. In fact there are fewer actual button presses during the long intervals than would be expected by chance. Moving window analyses performed on eye-fixation data reveal that no unique eye-event is associated with switching behavior. However, several indicators such as blink frequency, saccade frequency, and the direction of the saccade each are differentially sensitive to perceptual and response-related aspects of the switching process. The time course of these indicators depicts switching behavior as a process of cascaded stages.
AIP Conference Proceedings, 2004
Spatio-temporal dynamics of alpha activity during the resting state is characterized by alternati... more Spatio-temporal dynamics of alpha activity during the resting state is characterized by alternation between ordered and disordered states. The ordered state exhibits a variety of phase patterns. We found that the duration distributions of these states and phase patterns obey power laws. These results suggest that the appearance of phase patterns and the alternation between ordered and disordered states are not just due to noise but products of internal dynamics of the brain. We discuss the possibility that these dynamics are ...
ABSTRACT We tested the memory characteristics of visual search in an event-related potentials stu... more ABSTRACT We tested the memory characteristics of visual search in an event-related potentials study. Participants searched for a target letter presented among nontarget letters. We varied target identity (switch to new vs swap with nontarget from previous trial), nontarget identity (switch to new vs swap with target from previous trial), target location (repeat, switch, swap with nontarget), and nontarget location (repeat, switch, swap with target). Repeated target locations were responded to faster and more accurately than switched ones. There was a slowdown in performance when nontarget and target swapped their locations. The amplitude in the N2pc component was smaller when target location switched than repeated. The amplitude in the N1 component was highest when target and nontarget swapped their roles and target location switched; and smallest when both target and nontarget switched to new identity and target location repeated. These data show that visual search has memory for both target location and identity, but also nontarget identity and location play a role in processing.
Neuroreport, May 1, 2009
Selection of visual short-term memory content takes place during perceptual and postperceptual pr... more Selection of visual short-term memory content takes place during perceptual and postperceptual processing. We studied postperceptual selection in a change detection task, in which spatially distributed cues preceding the memory array marked potential change targets. In the 550-730 ms interval after the memory array onset but not in the following retention interval, event-related potentials showed larger contralateral delay activity when the spatial cues were selective than when they were unselective. This finding implies that distributed precueing strengthens the visual short-term memory representation during an extended memory consolidation phase. NeuroReport
Neuroscience and Behavioral Physiology, 1995
The stages of the mental rotation of complex three-dimensional figures were investigated in nine ... more The stages of the mental rotation of complex three-dimensional figures were investigated in nine healthy subjects using the intracortical interaction mapping technique. It was established that mental rotation is accomplished with the participation of both parietal regions; the prerotation setup is associated with the involvement of the frontal, central, and right temporal divisions of the brain; decision-making regarding the result of the rotation and the response is accomplished through the conjunction of both frontal and temporoparietooccipital regions of the left hemisphere. In the case of the unsuccessful solution of the problem the process seems to stop at the stage of the prerotation setup. With verbal control the configuration of the zone of high-level association during the first three stages is reminiscent of that observed in the baseline activity.
Physical Review E Statistical Nonlinear and Soft Matter Physics, Aug 1, 2007
We investigate patterns of collective phase synchronization in brain activity in awake, resting h... more We investigate patterns of collective phase synchronization in brain activity in awake, resting humans with eyes closed. The alpha range of human electroencephalographic activity is characterized by ever-changing patterns, with strong fluctuations in both time and overall level of phase synchronization. The correlations of these patterns are reflected in power-law scaling of these properties. We present evidence that the dynamics underlying this fluctuation is type-I intermittency. We present a model study illustrating that the scaling property and the collective intermittent dynamics are emergent features of globally coupled phase oscillators near the critical point of entering global frequency locking.
Journal of Cognitive Neuroscience, Dec 1, 2005
PloS one, 2016
Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain a... more Globally coherent patterns of phase can be obscured by analysis techniques that aggregate brain activity measures across-trials, whether prior to source localization or for estimating inter-areal coherence. We analyzed, at single-trial level, whole head MEG recorded during an observer-triggered apparent motion task. Episodes of globally coherent activity occurred in the delta, theta, alpha and beta bands of the signal in the form of large-scale waves, which propagated with a variety of velocities. Their mean speed at each frequency band was proportional to temporal frequency, giving a range of 0.06 to 4.0 m/s, from delta to beta. The wave peaks moved over the entire measurement array, during both ongoing activity and task-relevant intervals; direction of motion was more predictable during the latter. A large proportion of the cortical signal, measurable at the scalp, exists as large-scale coherent motion. We argue that the distribution of observable phase velocities in MEG is domina...
Perception Abstract, Feb 1, 2003
Page 1. Traveling Waves of Spontaneous Alpha EEG Activity phase synchronization method for spat... more Page 1. Traveling Waves of Spontaneous Alpha EEG Activity phase synchronization method for spatio-temporal EEG pattern analysis Junji Ito, Andrey R Nikolaev and Cees van Leeuwen Laboratory for Perceptual Dynamics ...
The aim of this study was to investigate an interaction between frontal and left temporo-parietal... more The aim of this study was to investigate an interaction between frontal and left temporo-parietal cortices in tasks requiring word association. A new method was used to examine averaged event-related potentials in different frequency bands by calculating correlation coef®cients between wavelet curves in distant cortical areas. This method was applied to previous event-related potentials recordings which found successive activation of frontal and left posterior areas . Correlated activity at 17 Hz was observed between frontal and left temporal (Wernicke's) areas prior to full activation of Wernicke's area. q
Zhurnal vysshei nervnoi deiatelnosti imeni I P Pavlova
Solution of spatial and verbal tasks was studied in 43 subjects using the advanced version of the... more Solution of spatial and verbal tasks was studied in 43 subjects using the advanced version of the method of intracortical interaction mapping (IIM) and analysis of EEG spectra in short (250 ms) intervals. Comparison between the IIM and coherence methods during solving simple motor tasks revealed some advantages of the IIM for studying of labile cortical connections. Several stages were separated in the process of solution of the mental task in accordance with patterns of cortical connections. The duration of the stages was similar in both kinds of tasks and corresponded to that revealed in psychological experiments. Cortical connections in the theta range were generalized and reflected the level of general tension. This unspecific tension was high for the whole period of the spatial task solution while in the verbal task the tension increased to the stage of decision making. Task-specific patterns were revealed in the beta range. The right parietal and temporal regions were the centers of EEG connections during solution of the spatial task while the left central area was essential for the verbal task solution. The left parietal area was involved in solution of both kinds of tasks. The frequency parameters of connections in the beta range were stable during the spatial task solving, and in the process of verbal task solving the dominant frequency changed after the initial (perception) stage probably due to switching to another thinking mechanism.
Zhurnal vysshei nervnoi deiatelnosti imeni I P Pavlova
The EEG spectral power in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) was studied durin... more The EEG spectral power in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) was studied during mental rotation of two- and three-dimensional objects. Only those EEG segments were analyzed which corresponded to the tasks with similar time of solving. The EEG spectral power of the alpha range was higher under control conditions than during task solving. The spectral power in the range of 15-45 Hz was higher under the operation than under the control conditions. This finding confirms the assumption that EEG desynchronization in the alpha range is accompanied by the high-frequency synchronization. The EEG high-frequency power was higher during mental rotation of two-dimensional objects than three-dimensional ones. Since the angular difference between the two-dimensional objects was larger than between the three-dimensional ones, the rotation angle rather than the "depth" of space increased cortical activation. Under experimental conditions, EEG spectral power in the range of 15-45 Hz was always the highest in the occipital areas, which was associated with the visual modality of stimuli. The EEG spectral power in the gamma range (35-45 Hz) was substantially higher at the first second of operation as compared with the second one testifying that EEG changes in this range are more related with the processes of perception and recognition than with mental operations with images.