Positive difference in ERPs reflects independent processing of visual changes

Bayesian estimation of group event-related potential components (BEGEP): testing a model for synthetic and real datasets

Objective.The spatial resolution of event-related potentials (ERPs) recorded on the head surface is quite low, since the sensors located on the scalp register mixtures of signals from several cortical sources. Bayesian models for multi-channel ERPs obtained from a group of subjects under multiple task conditions can aid in recovering signals from these sources.Approach.This study introduces a novel model that captures several important characteristics of ERP, including person-to-person variability in the magnitude and latency of source signals. Furthermore, the model takes into account that ERP noise, the main source of which is the background electroencephalogram, has the following properties: it is spatially correlated, spatially heterogeneous, and varies over time and from person to person. Bayesian inference algorithms have been developed to estimate the parameters of this model, and their performance has been evaluated through extensive experiments using synthetic data and real ERPs records in a large number of subjects (N= 351).Main results.The signal estimates obtained using these algorithms were compared with the results of the analysis of ERPs by conventional methods. This comparison showed that the use of this model is suitable for the analysis of ERPs and helps to reveal some features of source signals that are difficult to observe in their mixture signals recorded on the scalp.Significance.This study shown that the proposed method is a potentially useful tool for analyzing ERPs collected from groups of subjects in various cognitive neuroscience experiments.

Subjectively different emotional schematic faces not automatically discriminated from the brain's bioelectrical responses

The present study investigates how the brain automatically discriminates emotional schematic faces, as indicated by the mismatch responses, and how reliable these brain responses are. Thirty-three healthy volunteers participated in the vMMN EEG experiment with four experimental sets differing from each other by the type of standard (object with scrambled face features) and the type of deviants (Angry, Happy and Neutral schematic faces) presented. Conscious subjective evaluations of valence, arousal and attention catching of the same stimuli showed clear differentiation of emotional expressions. Deviant faces elicited rather similar vMMN at frontal and occipital sites. Bayesian analyses suggest that vMMN does not differ between angry and happy faces. Neutral faces, however, did not yield statistically significant vMMN at occipital leads. Pearson's correlation and intra-class correlation analyses showed that the brain's reactions to the stimuli were highly stable within individuals across the experimental sets, whereas the mismatch responses were much more variable.

Is It Implicit Detection or Perception During Change Blindness?

Purpose

Implicit detection differs from implicit perception. The former includes implicit registration, localisation, identification and comparison of an object. Implicit comparison is not necessary for implicit perception, and should not involve the identification or localisation of objects. While many studies have reported evidence of implicit detection in change blindness, they may, in fact, have only observed implicit perception. In this study, we aimed to find out whether there is implicit detection or perception during the change blindness period.

Methods

In Experiments 1 and 2, we used a simple change detection paradigm, coupled with a speeded attribute discrimination task. Reaction times (RTs) and accuracy of the participants were measured for the speeded attribute discrimination task. We compared differences in RT and accuracy of the invalid and congruent cue trials to find evidence for implicit detection. Invalid trials referred to stimuli where the appearance of the cue does not change, whereas congruent trials involved cued objects with the same attributes as that of the change object. In Experiment 3, a one-shot change detection experiment was conducted, where subjects were required to report whether the objects were the same or different as quickly as possible. We compared the differences in RTs between trials in which the stimulus exhibited a change but participants reported “same” (change blindness trails) and trials in which the stimulus exhibited no change and participants reported “same” (baseline trials), to find evidence for implicit perception.

Results

In Experiments 1 and 2, the difference in accuracy and RTs under invalid and congruent conditions was not significant. We did not observe a validity effect as evidence for implicit localisation or a congruency effect as evidence for identification. In Experiment 3, the RTs were longer in the change blindness relative no-change trials, which indicated that there was implicit perception.

Conclusion

The results of this study showed that there was no evidence supporting implicit detection in colour or orientation as a single or a combination of features. However, we report evidence for implicit perception during the change blindness period. Change may be implicitly perceived, but not located or identified before there is conscious detection.

Distilling the distinct contralateral and ipsilateral attentional responses to lateral stimuli and the bilateral response to midline stimuli for upper and lower visual hemifield locations

A contralateral posterior negativity elicited by lateral oddballs (N2pc) and a bilateral posterior negativity elicited by vertical midline oddballs (bilateral N2) are ERP components reflecting attentional deployment that have been rarely compared. In different tasks, we explored to what extent they reflect similar underlying mechanisms of attention. We used a multiple-frame procedure to present pop-out color oddballs among distractors. A homogeneous condition contained only distractors (0 oddballs) and served as a control condition that was subtracted from oddball-present conditions to isolate attention effects. The number of oddballs and the vertical hemifield containing them (upper vs. lower) were two critical factors. For the lower hemifield, the signal amplitude increased with the number of oddballs, otherwise had similar effects and scalp distributions, suggesting the bilateral N2 acted as a bilateral N2pc and likely reflected similar underlying generators. For the upper hemifield, component amplitude also increased with the number of oddballs, but the scalp distributions were positive and more centered, suggesting inverted generators across the two vertical hemifields. An ipsilateral positivity occurred about 50 ms after a contralateral positivity, similar in magnitude, producing a biphasic contra-minus-ipsi difference wave. Previously reported smaller negative N2pc components for upper hemifield oddballs likely reflected a negative lobe artificially created by the subtraction of a lagged positive ipsilateral response. The results compel us to argue for a systematic separation of data for upper versus lower hemifields in studies of visuo-spatial attention, and the use of an experimental design permitting the separate estimation of contralateral and ipsilateral responses.

Visual mismatch response and fMRI signal adaptation correlate in the occipital-temporal cortex

Several electrophysiological studies found response differences to a given stimulus when it is repeated frequently as compared to when it occurs rarely in oddball sequences. Initially defined in acoustic perception, such difference also exists in the visual modality and is referred to as visual mismatch negativity (vMMN). However, the repetition of a stimulus also leads to the reduction of the blood oxygen-level dependent (BOLD) signal (fMRI adaptation, fMRIa) when compared to alternating stimuli in fMRI experiments. So far no study compared the vMMN to fMRIa within the same paradigm and participants. Here we tested the possible connection between fMRIa and vMMN in a visual oddball paradigm in two separate sessions, acquiring electrophysiological and neuroimaging data for real and false characters from the same participants. We found significant visual mismatch response (vMM) as well as fMRIa for both character types. Importantly, the magnitude of the vMM over the CP1 electrode cluster showed a significant correlation with the fMRIa within the letter form area, for real characters. This finding suggests that similar neural mechanisms are responsible for the two phenomena.

Read My Lips: Brain Dynamics Associated with Audiovisual Integration and Deviance Detection

Information from different modalities is initially processed in different brain areas, yet real-world perception often requires the integration of multisensory signals into a single percept. An example is the McGurk effect, in which people viewing a speaker whose lip movements do not match the utterance perceive the spoken sounds incorrectly, hearing them as more similar to those signaled by the visual rather than the auditory input. This indicates that audiovisual integration is important for generating the phoneme percept. Here we asked when and where the audiovisual integration process occurs, providing spatial and temporal boundaries for the processes generating phoneme perception. Specifically, we wanted to separate audiovisual integration from other processes, such as simple deviance detection. Building on previous work employing ERPs, we used an oddball paradigm in which task-irrelevant audiovisually deviant stimuli were embedded in strings of non-deviant stimuli. We also recorded the event-related optical signal, an imaging method combining spatial and temporal resolution, to investigate the time course and neuroanatomical substrate of audiovisual integration. We found that audiovisual deviants elicit a short duration response in the middle/superior temporal gyrus, whereas audiovisual integration elicits a more extended response involving also inferior frontal and occipital regions. Interactions between audiovisual integration and deviance detection processes were observed in the posterior/superior temporal gyrus. These data suggest that dynamic interactions between inferior frontal cortex and sensory regions play a significant role in multimodal integration.

Differentiation of neuronal operations in latent components of event-related potentials in delayed match-to-sample tasks

The goal of this study was to decompose ERPs into latent components associated with hypothetical processes of category discrimination, comparison to working memory and action-related operations. In five variants of the delayed match-to-sample s1-s2 task, instructions were varied for manipulation of the processes. The blind source separation was applied to the collection of ERPs. The category discrimination operation is attributed to three latent components with peak latencies of 130 to 170 ms, which are generated in different parts of the prestriate cortex. The comparison to working memory operation is attributed to a latent component that is generated in the temporal cortex and manifested in a positive deflection with a peak latency of 250 ms after s2. The category discrimination and comparison to working memory effects were dissociated spatially and temporally from attention and action selection effects.

Neural adaptation to non-symbolic number and visual shape: an electrophysiological study

Several studies assumed that the analysis of numerical information happens in a fast and automatic manner in the human brain. Utilizing the high temporal resolution of electroencephalography (EEG) in a passive oddball adaptation paradigm, we compared event-related brain potentials (ERPs) evoked by unattended shape changes and unattended numerosity changes. We controlled visual stimulus properties in a stringent manner. Unattended changes in shape elicited significant, gradual adaptation effects in the range of early visual components, indicating the fast and automatic processing of shapes. Changes in numerosity did not elicit significant changes in these early ERP components. The lack of early number-specific effects was qualified by a significant interaction between Shape and Number conditions. Number change elicited gradual ERP effects only on late ERP components. We conclude that numerosity is a higher-level property assembled from naturally correlating perceptual cues and hence, it is identified later in the cognitive processing stream.

Sustained posterior contralateral activity indicates re-entrant target processing in visual change detection: an EEG study

The present study investigated the neural mechanisms that contribute to the detection of visual feature changes between stimulus displays by means of event-related lateralizations of the electroencephalogram (EEG). Participants were instructed to respond to a luminance change in either of two lateralized stimuli that could randomly occur alone or together with an irrelevant orientation change of the same or contralateral stimulus. Task performance based on response times and accuracy was decreased compared to the remaining stimulus conditions when relevant and irrelevant feature changes were presented contralateral to each other (contralateral distractor condition). The sensory response to the feature changes was reflected in a posterior contralateral positivity at around 100 ms after change presentation and a posterior contralateral negativity in the N1 time window (N1pc). N2pc reflected a subsequent attentional bias in favor of the relevant luminance change. The continuation of the sustained posterior contralateral negativity (SPCN) following N2pc covaried with response times within feature change conditions and revealed a posterior topography comparable to the earlier components associated with sensory and attentional mechanisms. Therefore, this component might reflect the re-processing of information based on sustained short-term memory representations in the visual system until a stable target percept is created that can serve as the perceptual basis for response selection and the initiation of goal-directed behavior.

Impairment in preattentive processing among patients with hypertension revealed by visual mismatch negativity

Objective. Patients with hypertension show deficits in cognitive function. However, the neural mechanisms underlying the preattentive information processing in hypertensive patients are poorly understood. We seek to investigate whether hypertensive patients have impairments in preattentive information processing. Methods. We compared visual mismatch negativity (vMMN) between 15 hypertensive patients and 15 age-matched healthy controls, which was elicited by the change of visual duration randomly presented in both peripheral visual fields. In addition, the global cognitive function for all participants was assessed with Mini-Mental State Examination (MMSE). Results. The vMMN in deviant-standard comparison was observed at occipital-temporal regions. Compared with normal healthy controls, the amplitude of vMMN was significantly decreased in hypertensive patients (P < 0.05). Meanwhile, the vMMN peak latency was delayed in the hypertensive group (P < 0.05). However, the MMSE scores of patients with hypertension were not significantly different from those of controls (P > 0.05), and there was no significant correlation between the mean amplitude of vMMN and SBP, DBP, and MMSE in hypertensive individuals, respectively. Conclusions. These data indicate dysfunction of automatically change detection processing in patients with hypertension. Moreover, the changes of vMMN provide a more objective and reliable assessment for cognitive impairment in hypertensive patients.

Atypical visual change processing in children with autism: an electrophysiological study

Children with Autism Spectrum Disorder (ASD) may display atypical behaviors in reaction to unattended changes that occur in all sensory modalities. Atypical automatic auditory change processing has been highlighted in ASD via the analysis of mismatch negativity (MMN). The present study investigated visual deviancy detection in children with ASD in order to determine whether unusual reactions to change operate in other sensory modalities. Twelve children with ASD were presented with a passive visual oddball paradigm using dynamic stimuli. Compared to controls, children with ASD showed an earlier visual mismatch response, suggesting a hypersensitivity to visual deviancy. This study is thus consistent with the hypothesis of the existence of "general" atypical change detection processing in children with ASD that might contribute to their intolerance of change.

Mismatch Negativity Does Not Show Evidence of Memory Reactivation in the Visual Modality

The possibility of reactivation of the memory representation underlying visual mismatch negativity (vMMN) was investigated in a modified passive roving-standard paradigm. Stimuli (arrays of Gábor patches) were presented in sequences with blank interval between the sequences. The first member of each sequence was identical to the standard of the previous sequence, while the second stimulus had different orientation therefore the second stimulus was considered as deviant. In a control condition the stimuli of the previous sequence had random orientations. Event-related potentials (ERPs) in response to the deviants were compared to ERPs in response to the (physically identical) second stimulus of the control sequences. The comparison showed emergence of a positive component at an early (98–132 ms) latency range elicited by deviants. This component is interpreted as an index of increased sensitivity to rare changes in sequences dominated by identical stimuli rather than a component specific to violation of sequential regularity. Consequently, contrary to the findings in the auditory modality, the first stimulus of the sequence did not reactivate the memory representation underlying the vMMN, since subsequent deviant elicited no vMMN.

Visual mismatch negativity reveals automatic detection of sequential regularity violation

Sequential regularities are abstract rules based on repeating sequences of environmental events, which are useful to make predictions about future events. Here, we tested whether the visual system is capable to detect sequential regularity in unattended stimulus sequences. The visual mismatch negativity (vMMN) component of the event-related potentials is sensitive to the violation of complex regularities (e.g., object-related characteristics, temporal patterns). We used the vMMN component as an index of violation of conditional (if, then) regularities. In the first experiment, to investigate emergence of vMMN and other change-related activity to the violation of conditional rules, red and green disk patterns were delivered in pairs. The majority of pairs comprised of disk patterns with identical colors, whereas in deviant pairs the colors were different. The probabilities of the two colors were equal. The second member of the deviant pairs elicited a vMMN with longer latency and more extended spatial distribution to deviants with lower probability (10 vs. 30%). In the second (control) experiment the emergence of vMMN to violation of a simple, feature-related rule was studied using oddball sequences of stimulus pairs where deviant colors were presented with 20% probabilities. Deviant colored patterns elicited a vMMN, and this component was larger for the second member of the pair, i.e., after a shorter inter-stimulus interval. This result corresponds to the SOA/(v)MMN relationship, expected on the basis of a memory-mismatch process. Our results show that the system underlying vMMN is sensitive to abstract, conditional rules. Representation of such rules implicates expectation of a subsequent event, therefore vMMN can be considered as a correlate of violated predictions about the characteristics of environmental events.

Electrophysiological Evidence for Different Types of Change Detection and Change Blindness

Numerous studies have demonstrated that observers often fail to notice large changes in visual scenes, a phenomenon known as change blindness. Some experiments have suggested that phenomenological experience in change blindness experiments is more diverse than the common distinction between change detection and change blindness allows to resolve. Recently, it has been debated whether changes in visual scenes can be detected (“sensed”) without a corresponding perception of the changing object (“seeing”) and whether these phenomena build on fundamentally different perceptual processes. The present study investigated whether phenomenologically different perceptual processes such as sensing and seeing rely on different or similar neural processes. We studied ERP effects of visual change processing (as compared to change blindness) when observers merely detected the presence of a change (“sensing”) and when they identified the changing object in addition to detection (“seeing”). Although the visual awareness negativity (VAN)/selection negativity was similar for detection with and without identification, a change-related positivity and the N2pc contralateral to changes were found exclusively when the change was fully identified. This finding indicates that change identification requires perceptual and neural processes that are not involved in mere detection. In a second experiment, we demonstrated that the VAN and N2pc effects are similar to effects of selective attention in a visual search task. By contrast, the change-related positivity was specific for conscious processing of visual changes. The results suggest that changes can be detected (“sensed”) without perception of the changing object. Furthermore, sensing and seeing seem to rely on different neural processes and seem to constitute different types of visual perception. These findings bear implications for how different categories of visual awareness are related to different stages in visual processing.

Human Visual System Automatically Encodes Sequential Regularities of Discrete Events

For our adaptive behavior in a dynamically changing environment, an essential task of the brain is to automatically encode sequential regularities inherent in the environment into a memory representation. Recent studies in neuroscience have suggested that sequential regularities embedded in discrete sensory events are automatically encoded into a memory representation at the level of the sensory system. This notion is largely supported by evidence from investigations using auditory mismatch negativity (auditory MMN), an event-related brain potential (ERP) correlate of an automatic memory-mismatch process in the auditory sensory system. However, it is still largely unclear whether or not this notion can be generalized to other sensory modalities. The purpose of the present study was to investigate the contribution of the visual sensory system to the automatic encoding of sequential regularities using visual mismatch negativity (visual MMN), an ERP correlate of an automatic memory-mismatch process in the visual sensory system. To this end, we conducted a sequential analysis of visual MMN in an oddball sequence consisting of infrequent deviant and frequent standard stimuli, and tested whether the underlying memory representation of visual MMN generation contains only a sensory memory trace of standard stimuli (trace-mismatch hypothesis) or whether it also contains sequential regularities extracted from the repetitive standard sequence (regularity-violation hypothesis). The results showed that visual MMN was elicited by first deviant (deviant stimuli following at least one standard stimulus), second deviant (deviant stimuli immediately following first deviant), and first standard (standard stimuli immediately following first deviant), but not by second standard (standard stimuli immediately following first standard). These results are consistent with the regularity-violation hypothesis, suggesting that the visual sensory system automatically encodes sequential regularities. In combination with a wide range of auditory MMN studies, the present study highlights the critical role of sensory systems in automatically encoding sequential regularities when modeling the world.

Event-related potentials reveal rapid registration of features of infrequent changes during change blindness

Background

Change blindness refers to a failure to detect changes between consecutively presented images separated by, for example, a brief blank screen. As an explanation of change blindness, it has been suggested that our representations of the environment are sparse outside focal attention and even that changed features may not be represented at all. In order to find electrophysiological evidence of neural representations of changed features during change blindness, we recorded event-related potentials (ERPs) in adults in an oddball variant of the change blindness flicker paradigm.

Methods

ERPs were recorded when subjects performed a change detection task in which the modified images were infrequently interspersed (p = .2) among the frequently (p = .8) presented unmodified images. Responses to modified and unmodified images were compared in the time window of 60-100 ms after stimulus onset.

Results

ERPs to infrequent modified images were found to differ in amplitude from those to frequent unmodified images at the midline electrodes (Fz, Pz, Cz and Oz) at the latency of 60-100 ms even when subjects were unaware of changes (change blindness).

Conclusions

The results suggest that the brain registers changes very rapidly, and that changed features in images are neurally represented even without participants' ability to report them.

Event-related brain potential evidence for implicit change detection: a replication of Fernandez-Duque et al. (2003)

Change blindness studies using explicit behavioral measures have revealed that humans are remarkably poor at explicitly detecting changes between two successive visual images until focused attention is drawn to the changes, which supports the notion that outside the range of focused attention, our mental representations of the visual world are so volatile as to be unable to support detection of changes. However, change blindness studies using implicit behavioral measures have revealed that changes outside the range of focused attention might be detected even in the absence of awareness, which supports the possibility that our mental representations are not so volatile as has been suggested. The purpose of the present study was to provide further evidence for implicit change detection using event-related brain potentials (ERPs). For this purpose, we compared ERPs elicited on trials where color changes were present but participants failed to report the presence of changes (Change blindness trials) and ERPs on trials where changes were absent and participants correctly did not report the presence of changes (No-change trials). The result showed that compared to No-change trials, Change blindness trials elicited a frontal/central positivity at around 160-180ms, which is highly consistent with the result of Fernandez-Duque et al. [D. Fernandez-Duque, G. Grossi, I.M. Thornton, H.J. Neville, Representation of change: separate electrophysiolocal markers of attention, awareness, and implicit processing, J. Cogn. Neurosci. 15 (2003) 491-507] who firstly reported an ERP correlate of implicit change detection. This result provides further evidence for implicit change detection, which supports the notion that even outside the range of focused attention, our mental representations of the visual world are robust at least enough to support implicit detection of changes.

Neural correlates of colour categories

This study used an electrophysiological marker of visual detection to investigate adults' processing of colour difference. Event-related potentials were collected from the identical colour (green: G0) presented as the frequent or infrequent stimulus within different colour contexts. Critically, we compared differences within the same colour category (G0 vs. green: G1) to differences between colour categories (G0 vs. blue and G0 vs. red). All differences showed a change-related positivity with similar scalp distribution. It was, however, not simply the magnitude of colour difference that reduced the latencies of the change-related positivity. A change in colour category without a magnitude difference also reduced latency of the event-related potential. Thus, for the first time we report an independent neural correlate of a colour category.

The mismatch negativity (MMN) in basic research of central auditory processing: a review

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Visual Mismatch Negativity

The visual homolog of the (auditory) mismatch negativity, the vMMN, has already been reviewed ( Pazo-Alvarez, Cadaveira, & Amenedo, 2003 ), but a considerable body of more recent research exists. The present paper concentrates on two crucial issues of vMMN research. These issues are the memory-dependence of the vMMN and the problem of attentive vs. nonattentive processing in vMMN research. While both issues require further clarification, vMMN seems to be a promising index of the nonattentional registration of the violation of environmental rules in the visual word.

ERPs and deviance detection: Visual mismatch negativity to repeated visual stimuli

Previous studies showed a visual analogue of the mismatch negativity (MMN) event-related potential (ERP), which is elicited by violating some sensory regularity. Separating physical change from violating a regularity, here we show that the visual MMN (vMMN) is elicited by regularity violations that do not involve physical stimulus change. Adult participants were presented with a series of red-black and green-black checkerboard patterns delivered regularly in an RRGGRRGG ... order. Infrequently (p=0.1) this regularity was broken by repeating a stimulus one additional time (e.g. RRGGRRR). ERPs elicited by irregular stimulus repetitions were negatively displaced compared to those elicited both by regular repetition and regular change in two latency ranges: 100-140 ms and 220-260 ms. Whereas the first of these two negative ERP differences appears to be sensitive to stimulus repetition per se, the second difference can be identified as a vMMN response to violating the sequential regularity. Thus, similarly to its auditory counterpart, vMMN reflects deviance-(regularity-violation) rather than change-detection processes.

Probability-independent and -dependent ERPs reflecting visual change detection

In ERP studies, two posterior components with different polarities have been identified as ERP correlates of visual change detection. To compare these components in terms of sensitivity to the preceding stimulus sequence, two peripheral stimuli of different colors (red and blue) were presented with equal (50:50) or different probabilities (20:80 or 80:20), while 12 participants performed shape discrimination at a central location. A posterior positivity at around 90-140 ms was observed with similar amplitude to all stimuli immediately preceded by a different stimulus. In contrast, a posterior negativity at around 140-180 ms was observed to increase in amplitude with increasing number of preceding different stimuli. These results suggest the existence of probability-independent and -dependent change processing in the human visual system. The functional significance is discussed in terms of memory-based comparison and stimulus-specific refractoriness.

An ERP study of visual change detection: effects of magnitude of spatial frequency changes on the change-related posterior positivity

In event-related brain potential (ERP) studies using a visual S1-S2 matching task, change stimuli elicit a posterior positivity at around 100-200 ms. In the present study, we investigated the effects of magnitude of spatial frequency changes on change-related positivity. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., NO-change, p=.40), (2) different from S1 in spatial frequency only (SF-change, .40), (3) different in orientation only (OR-change, .10), or (4) different in both spatial frequency and orientation (BOTH-change, .10). Further, three magnitude conditions (Large, Medium, and Small) were used to examine the effect of the magnitude of the spatial frequency change. Participant's (N=12) task was to respond to S2 with a change in orientation (from vertical to horizontal, or from horizontal to vertical) regardless of the spatial frequency of the stimulus. Changes in the spatial frequency elicited change-related positivity at a latency range of about 120-180 ms, which was followed by a central negativity (N270) and a late positive component (LPC). The amplitude of the change-related positivity tends to be enhanced as the magnitude of the change is increased. These results support the notion that the change-related positivity reflects memory-based change detection in the human visual system.

Neural correlates of preattentive and attentive processing of visual changes

To identify electrophysiological correlates of pre-attentive and attentive processing of visual changes, we compared event-related brain potentials in response to color changes at attended and unattended spatial locations using a visual S1-S2 matching task. The results showed that compared to no change, change stimuli elicited occipito-temporal positivity at around 100-160 ms (change-related positivity) and subsequent central negativity at around 220-300 ms (N270). Change-related positivity was observed in response to changes at both attended and unattended locations, while N270 was observed only when attention was directed to the location of the changes. These results suggest that change-related positivity reflects the pre-attentive processing of visual changes and N270 reflects the attentive processing of visual changes in the human brain.

Independent processing of visual stimulus changes in ventral and dorsal stream features indexed by an early positive difference in event-related brain potentials

In event-related brain potential (ERP) studies of brain activity using a visual S1-S2 matching task, change stimuli elicit a posterior positive component with a latency of 100-200 ms. To elucidate the hierarchical organization of the processing of a visual stimulus change based on multiple stimulus features, ERPs were recorded in 12 participants performing an S1-S2 matching task with stimuli defined by color (mediated by the ventral stream) and motion direction (mediated by the dorsal stream). Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., no change), (2) different from S1 in color only (color change), (3) different in motion direction only (motion direction change), or (4) different in both color and motion direction (color-motion direction change). These trials were presented in random order with equal probability, and the participants were asked to respond to one of these trials in separate blocks. Relative to the no-change stimulus, the three types of change stimuli elicited posterior positivities. The scalp-topography of change positivities differed according to the feature changed. In addition, the amplitude and scalp-topography of change positivities in response to a conjunction change were the respective sums of those in response to changes in the corresponding single features. These results suggest that the change detection system reflected by the change positivity is separate for each feature dimension, and these operate independently.