Electrophysiological responses to visuospatial regularity

Humans are quicker to detect reflectional than rotational or translational symmetry, despite the fact that these patterns are equally regular. We were interested in the neural correlates of these perceptual effects. Participants viewed random, reflection, rotation, and translation patterns while we recorded EEG from the scalp. Half the participants classified the pattern regularity overtly, the other half did not explicitly attend to pattern regularity but reported rare oddball trials, where two squares were embedded among the dots. The amplitude of a symmetry‐related ERP known as the sustained posterior negativity was most pronounced for reflection, then rotation and translation. We suggest that reflectional symmetry, despite its biological significance, may not be processed by unique visual mechanisms, but instead it could be a preferred stimulus for a more general regularity‐sensitive network in the extrastriate visual cortex.     

Effects of learning on color-form conjunction in macaque inferior temporal neurons

Many neurons in area TE of the macaque respond selectively to colors or forms. One problem remaining is how these neurons contribute to conjunctive perception of these features when there are many objects in their receptive fields. In order to investigate the effects of learning on neural activities for the conjunction of color and form, neurons were recorded during a visual fixation task and two go/no-go visual discrimination tasks. One discrimination task involved conjunction of color and form for successively presented colored patterns. In this task, the monkeys were required to hold two go stimuli in the transient memory. The other task involved associative discrimination between the form of gray patterns and the color of irregular textures when the two features were presented simultaneously at separate locations. Each of the two stimuli was neutral in the go/no-go behavior in the latter task. One third of responsive neurons showed a significant interaction of color and form in response to the colored patterns during the conjunction task. Responses of these neurons were mostly enhanced for a particular colored pattern, which was usually one of the go stimuli. The response enhancement was preserved when the go stimulus was presented with a distractor. However, this change was not seen during the associative discrimination task. During the fixation task, the neurons that showed interaction of color and form in the conjunction task were usually selective either for the forms of gray patterns or colors of irregular textures, and only a few neurons were selective for both. The results indicate that neurons in area TE can conjoin color and form actively for an object held in the working memory, suppressing illusory conjunction.     

Unnoticed regularity violation elicits change-related brain activity

Event-related brain electric activity (ERP) was investigated to unnoticed visual changes. The orientation of grid elements (vertical or horizontal) changed after the presentation of 10–15 identical stimuli. The grid patterns were task irrelevant, and were presented in the background of a shape discrimination task. During the first half of the session, participants were unaware of the stimulus change. However, in comparison to the ERPs to the fifth identical stimuli, stimulus change elicited posterior negativities in the 270–375 ms range (visual mismatch negativity, vMMN). With participants instructed on the stimulus change, negativities emerged with earlier onset and with wider distribution. When stimulus change was preceded by only two identical stimuli, there were no such ERP effects. As the results show, a longer sequence of identical unattended stimuli may establish the memory representation of stimulus regularity, and violation of regularity is indicated by posterior negative ERP components (vMMN).     

Attention‐dependent sound offset‐related brain potentials

When performing sensory tasks, knowing the potentially occurring goal‐relevant and irrelevant stimulus events allows the establishment of selective attention sets, which result in enhanced sensory processing of goal‐relevant events. In the auditory modality, such enhancements are reflected in the increased amplitude of the N1 ERP elicited by the onsets of task‐relevant sounds. It has been recently suggested that ERPs to task‐relevant sound offsets are similarly enhanced in a tone‐focused state in comparison to a distracted one. The goal of the present study was to explore the influence of attention on ERPs elicited by sound offsets. ERPs elicited by tones in a duration‐discrimination task were compared to ERPs elicited by the same tones in not‐tone‐focused attentional setting. Tone offsets elicited a consistent, attention‐dependent biphasic (positive‐negative—P1‐N1) ERP waveform for tone durations ranging from 150 to 450 ms. The evidence, however, did not support the notion that the offset‐related ERPs reflected an offset‐specific attention set: The offset‐related ERPs elicited in a duration‐discrimination condition (in which offsets were task relevant) did not significantly differ from those elicited in a pitch‐discrimination condition (in which the offsets were task irrelevant). Although an N2 reflecting the processing of offsets in task‐related terms contributed to the observed waveform, this contribution was separable from the offset‐related P1 and N1. The results demonstrate that when tones are attended, offset‐related ERPs may substantially overlap endogenous ERP activity in the postoffset interval irrespective of tone duration, and attention differences may cause ERP differences in such postoffset intervals.     

How personal earthquake experience impacts on the Stroop interference effect: An event‐related potential study

Event‐related brain potentials (ERPs) were measured when 24 Chinese subjects performed the classical Stroop task. All of subjects had experienced the great Sichuan earthquake (5/12), with 12 people in each of the Far (Chengdu city) and the Close (Deyang city) earthquake experience groups. The behavioral data showed that the Stroop task yielded a robust Stroop interference effect as indexed by longer RT for incongruent than congruent color words in both the Chengdu and Deyang groups. Scalp ERP data showed that incongruent stimuli elicited a more negative ERP deflection (N400–600; Stroop interference effect) than did congruent stimuli between 400–600 ms in the Chengdu group, while the Stroop interference ERP effect was not found in the Deyang group. Dipole source analysis localized the generator of the N400–600 in the right prefrontal cortex (PFC) and was possibly related to conflict monitoring and cognitive control.     

Differences in ERP topographies during color matching of smoking-related and neutral pictures in smokers and non-smokers.

The concept of a specific memory network that drives addictive behavior has often been discussed in relation to the phenomenon of sudden relapse into addiction after years of abstinence. But there is still a lack of data that shows a link between drug-related cue processing and specific changes of behavior in addicts. In the present study we investigated the relationship between smoking-related picture processing, performance in a color matching task, and ERP topographies. Fifteen smokers and 19 non-smoking participants performed a color matching task including monochromic pictures with smoking-related and neutral content. Smokers and non-smokers showed remarkable differences between stimulus category-related ERP topographies. Furthermore, both smokers and non-smokers showed increased reaction times during color matching when the picture contents were related to smoking behavior. The results are discussed with respect to different drug-cue-related patterns of information processing in smokers and non-smokers.     

Do different perceptual task sets modulate electrophysiological correlates of masked visuomotor priming? Attention to shape and color put to the test

According to classical theories, automatic processes operate independently of attention. Recent evidence, however, shows that masked visuomotor priming, an example of an automatic process, depends on attention to visual form versus semantics. In a continuation of this approach, we probed feature‐specific attention within the perceptual domain and tested in two event‐related potential (ERP) studies whether masked visuomotor priming in a shape decision task specifically depends on attentional sensitization of visual pathways for shape in contrast to color. Prior to the masked priming procedure, a shape or a color decision task served to induce corresponding task sets. ERP analyses revealed visuomotor priming effects over the occipitoparietal scalp only after the shape, but not after the color induction task. Thus, top‐down control coordinates automatic processing streams in congruency with higher‐level goals even at a fine‐grained level.     

Interactions of age of acquisition and lexical frequency effects with phonological regularity: An ERP study

Across languages, lexical frequency and age of acquisition (AoA) are important predictors of word reading that are naturally correlated, and both variables have been shown to interact with phonological regularity. Previous behavioral findings in Chinese have shown stronger regularity effects in low frequency relative to high frequency characters. Meanwhile, the arbitrary mapping hypothesis predicts stronger interference effects in late‐acquired irregular words. This study examined the neural bases of these phenomena in Chinese using a delayed naming task with 480 single characters. Single‐trial ERP analyses were conducted to contrast the interactions of frequency or AoA effects with phonological regularity, while controlling for the other factor. Results showed differential and significant effects of AoA and frequency at the N400 and late positive component (LPC), respectively, indicating their independence. ERP interaction patterns of frequency and regularity in Chinese were observed for the first time in the LPC time window and suggested semantic interference from sublexical units during character reading. Interaction of AoA and regularity at the N400 could be explained by the semantic hypothesis but appeared inconsistent with the arbitrary mapping hypothesis.     

Human efficiency for symmetry detection on 3D bumpy surfaces

Based on the ideal observer analysis, we investigated sampling properties of image information used by human visual system, for symmetrical pattern discrimination on 3D bumpy surface. There were three models of ideal observer (IO) to perform the task: 2D-IO using 2D projection image (i.e., retinal image), 2.5D-IO using image transformed to canonical view, and 3D-IO using recovered pattern image of 2D plane. We measured discrimination thresholds on the task for each IO model and subjects, and calculated human statistical efficiency relative to each ideal observer. The results indicated for the detection of a diagonal symmetry in the bumpy surface that human performance was similar to 3D-IO. This implies that human observers use the structure of the bumpy surface to detect the diagonal symmetry.     

Single trial ERP reading based on parallel factor analysis

The extraction of task‐related single trial ERP features has recently gained much interest, in particular in simultaneous EEG‐fMRI applications. In this study, a specific decomposition known as parallel factor analysis (PARAFAC) was used, in order to retrieve the task‐related activity from the raw signals. Using visual detection task data, acquired in normal circumstances and simultaneously with fMRI, differences between distinct task‐related conditions can be captured in the trial signatures of specific PARAFAC components when applied to ERP data arranged in Channels × Time × Trials arrays, but the signatures did not correlate with the fMRI data. Despite the need for parameter tuning and careful preprocessing, the approach is shown to be successful, especially when prior knowledge about the expected ERPs is incorporated.     

Alcohol words elicit reactive cognitive control in low‐sensitivity drinkers

Previous ERP studies shown support for the idea that alcohol‐related stimuli are particularly salient to individuals who report low sensitivity (LS) to alcohol's effects (a known risk factor for alcohol‐related problems), leading such stimuli to spontaneously capture their attention and interfere with self‐regulatory goal pursuit. The current study investigated LS individuals' use of reactive and proactive cognitive control in response to alcohol‐related stimuli. Participants performed an alcohol Stroop task in which they indicated the font color of alcohol‐ and nonalcohol‐related words while ERPs were recorded. The probability of alcohol and nonalcohol words was manipulated to test predictions derived from Dual Mechanisms of Control theory. Among LS individuals, infrequent alcohol‐related words elicited slower responses and larger N2 amplitude, consistent with these stimuli eliciting enhanced reactive control responses. Amplitude of the frontal slow wave (FSW) component, associated with proactive control, was marginally larger among LS individuals when alcohol words were more frequent, but response accuracy was lower. These findings demonstrate that LS individuals experience conflict when presented with task‐irrelevant alcohol‐related stimuli, even in a context where conflict arguably should not be present. Findings further suggest that LS individuals can effectively implement reactive control to deal with this conflict when it is infrequent but have difficulty implementing proactive control in the context of more frequent conflict.     

Linking visual gamma to task‐related brain networks—a simultaneous EEG‐fMRI study

There is a growing interest in human gamma‐band oscillatory activity due to its direct link to neuronal populations, its associations with many cognitive processes, and its positive relationship with fMRI BOLD signal. Visual gamma has been successfully detected using concurrent EEG‐fMRI recordings and linked to activity in the visual cortex using voxel‐wise regression analysis. As gamma‐band oscillations reflect predominantly feedforward projections between brain regions, its inclusion in functional connectivity analysis is highly recommended; however, very few studies have investigated this line of research. In the current study, we aimed to explore this gap by asking which fMRI brain network is related to gamma activity induced by the color discrimination task. Advanced denoising strategies and multitaper spectral decomposition were applied to EEG data to detect gamma oscillations, and group independent component analysis was performed on fMRI data to identify task‐related neural networks. Despite using only trials without motor response (50% of the trials), the two neural measures were successfully coupled. One of the six task‐related networks, the occipito‐parietal network, exhibited significant trial‐by‐trial covariations with gamma oscillations. In addition to the expected extrastriate visual cortex, the network encompasses extensive brain activations in the precuneus, bilateral intraparietal, and anterior insular cortices. We argue that the visual cortex is the source of gamma, whereas the remaining brain regions exhibit feedforward and feedback connections related to this oscillatory activity. Our findings provide evidence for the electrophysiological basis of the connectivity revealed by BOLD signal and impart novel insights into the neural mechanism of color discrimination.     

Interactions of visual stimuli in the receptive fields of inferior temporal neurons in awake macaques

Summary Monkeys were trained to perform a fixation task and a visual discrimination task. During the fixation task, one or two light bars were presented at different positions in the receptive fields of TE neurons. During the discrimination task, the animal was required to detect the positive stimulus when one or two of the paired small colored spots or two-dimensional patterns were presented. In both behavioral conditions, when the two light stimuli were presented simultaneously, almost none of the TE neurons showed an increase in responding over the single stimulus condition; the response was usually similar or less than the stronger response in the single stimulus condition. In the neurons that responded selectively to the discriminanda during the discrimination task, various interactions between the two antagonistic stimuli occurred depending on the location or the effectiveness of the two stimuli. These results may be related to gain control mechanisms in the wide receptive fields of TE neurons.     

Contextual task difficulty modulates stimulus discrimination: Electrophysiological evidence for interaction between sensory and executive processes

The occipital‐temporal N1 component of the event‐related potential (ERP) has previously been shown to index a stimulus discrimination process. However, the N1 has not consistently been shown to be sensitive to the difficulty of stimulus discrimination. Here, we manipulated the difficulty of stimulus discrimination by modulating the similarity between serially presented targets and nontargets. The same target stimulus was employed in both easy and difficult discrimination contexts, and these physically identical target stimuli elicited a larger N1 and smaller P3b in the difficult task context. Moreover, when targets were incorrectly categorized, N1 amplitude was diminished and a P3b was not elicited. These findings provide evidence that the N1 component reflects a sensory discrimination process that is modulated by executive control, and that this component can index discrimination errors when stimulus discrimination is difficult.     

Color categories affect pre-attentive color perception

Categorical perception (CP) of color is the faster and/or more accurate discrimination of colors from different categories than equivalently spaced colors from the same category. Here, we investigate whether color CP at early stages of chromatic processing is independent of top-down modulation from attention. A visual oddball task was employed where frequent and infrequent colored stimuli were either same- or different-category, with chromatic differences equated across conditions. Stimuli were presented peripheral to a central distractor task to elicit an event-related potential (ERP) known as the visual mismatch negativity (vMMN). The vMMN is an index of automatic and pre-attentive visual change detection arising from generating loci in visual cortices. The results revealed a greater vMMN for different-category than same-category change detection when stimuli appeared in the lower visual field, and an absence of attention-related ERP components. The findings provide the first clear evidence for an automatic and pre-attentive categorical code for color.     

A parietal‐to‐frontal shift in the P300 is associated with compensation of tactile discrimination deficits in late middle‐aged adults

Tactile perception declines with age on both behavioral and neurophysiological levels. Less well understood is how neurophysiological changes relate to tactile discrimination performance in middle adulthood. A tactile discrimination task was conducted while ERPs were measured in three groups of healthy adults aged 20 to 66 years. Accuracy was lowest in late middle adulthood (56–66 years) while somatosensory ERP components (P50, N70, P100, N140) were comparable across age groups. The cognitive P300 revealed age‐related differences in scalp distribution typical for older adults to already be present in late middle adulthood. Increased recruitment of frontal cognitive processes was positively related to performance in later middle adulthood. Our results further the understanding of age‐related differences in tactile perception during middle adulthood and the importance of cognitive processes to compensate for age‐related decline.     

Attenuation of auditory ERPs to action‐sound coincidences is not explained by voluntary allocation of attention

The event‐related potential (ERP) correlates of sound detection are attenuated when eliciting sounds coincide with our own actions. The role of attention in this effect was investigated in two experiments by presenting tones separated by random intervals. In the homogeneous condition of Experiments 1 and 2, the same tone was repeated, whereas in the mixed condition of Experiment 1, tones with five different frequencies were presented. Participants performed a time‐interval production task by marking intervals with keypresses in Experiment 1, and tried to produce keypress‐tone coincidences in Experiment 2. Although the auditory ERPs were attenuated for coincidences, no modulation by the multiplicity of tone frequencies in Experiment 1, or by the task‐relevancy of tones and coincidences in Experiment 2, was found. This suggests that coincidence‐related ERP attenuation cannot be fully explained by voluntary attentional mechanisms.     

Goal relevance influences performance monitoring at the level of the FRN and P3 components

The feedback‐related negativity (FRN) provides a reliable ERP marker of performance monitoring (PM). It is usually larger for negative compared to positive feedback, and for unexpected relative to expected feedback. In two experiments, we assessed whether these effects could be modulated by goal relevance, defined as feedback informativeness (reliability) and/or impact on a person's goals. EEG (64‐channel) was recorded while 30 participants (in each experiment) performed a speeded go/no‐go task across blocks in which the feedback on task performance was deemed either relevant or not. At the ERP level, the FRN component was larger for (frequent) negative compared to (deviant) positive feedback exclusively when the feedback was relevant (Experiment 1). When the probability of positive and negative feedback was balanced (Experiment 2), this valence‐driven FRN effect was absent. However, across these two experiments, the FRN was always larger for irrelevant than relevant feedback. Moreover, the subsequent P300 component was larger for feedback in the relevant than the irrelevant blocks. This effect was valence unspecific in Experiment 1, while in Experiment 2 larger P3 amplitudes were recorded for negative than positive (relevant) feedback. Across the two experiments, a larger correct‐related negativity in the irrelevant than relevant context was also observed, suggesting that PM is flexible. These ERP findings indicate that goal relevance influences feedback (and response) processing during PM, with two nonoverlapping neurophysiological effects: It gates reward prediction error brain mechanisms (FRN effect), before enhancing subsequent motivational processes (P300 effect).     

Statistical efficiency of the object recognition with wire-frame stimuli

To investigate whether internal object representations in the brain are 2D or 3D, we measured discrimination thresholds and calculated statistical efficiencies in the object recognition task based on the ideal observer analysis. Stimulus images were created by orthographic projection of 3D wire-frame objects on a fronto-parallel plane. The discrimination task with the wire-frame stimuli was performed in the monocular (Experiment 1) and the binocular (Experiment 2) conditions. The results indicate that the subjects' statistical efficiencies relative to the 2D ideal observer exceeded 100%, suggesting that the internal object representations should be 3D. In addition, the results revealed that the object type with high-level symmetry led to better discrimination in both experiments. Furthermore, the interaction between 3D cue values and the object regularity was suggested to cause the viewpoint dependency.     

Is the 45 degrees-oblique a third dominant direction?

Vertical and horizontal are widely accepted as dominant directions or norms of visual orientation in the frontoparallel plane. They are supposed to cause a normalization effect consisting in the apparent rotation of a tilted straight line towards the nearest dominant direction. The evidence for tilt normalization towards the vertical or horizontal visual meridia is indirect. On the other hand, human observers are very sensitive to departures from the vertical and horizontal, which means that most orientations in the frontoparallel plane are termed tilted rather than vertical or horizontal. By measuring directly the orientation of dot patterns we found that estimated orientation was systematically biased towards the nearest 45 degrees-oblique visual meridian. This finding is interpreted as evidence for the existence of an oblique norm in visual tilt.