Object‐substitution masking modulates spatial attention deployment and the encoding of information in visual short‐term memory: Insights from occipito‐parietal ERP components

If object‐substitution masking (OSM) arises from mask representations replacing target representations, OSM should impede the formation of representations in visual short‐term memory (VSTM). We utilized event‐related potentials to examine the effect of OSM on target processing. An N2pc was observed on trials with delayed‐offset masks, indicating that focused attention was directed to the target. The sustained posterior contralateral negativity (SPCN), an index of VSTM storage, was observed in delayed‐offset trials only on trials with correct responses. This supports the hypothesis that inaccurate performance on delayed‐offset trials arises from a failure to encode the target in VSTM. On co‐termination trials, accuracy was high and neither the N2pc nor SPCN was observed. This indicates that, in the absence of masking, the task was accomplished by maintaining a diffuse attentional state that enabled the joint encoding of the potential target items.     

Spatial layout of letters in nonwords affects visual short‐term memory load: Evidence from human electrophysiology

The sustained posterior contralateral negativity (SPCN) was used to investigate the effect of spatial layout on the maintenance of letters in VSTM. SPCN amplitude was measured for words, nonwords, and scrambled nonwords. We reexamined the effects of spatial layout of letters on SPCN amplitude in a design that equated the mean frequency of use of each position. Scrambled letters that did not form words elicited a larger SPCN than either words or nonwords, indicating lower VSTM load for nonwords presented in a typical horizontal array than the load observed for the same letters presented in spatially scrambled locations. In contrast, prior research has shown that the spatial extent of arrays of simple stimuli did not influence the amplitude of the SPCN. Thus, the present results indicate the existence of encoding and VSTM maintenance mechanisms specific to letter and word processing.     

On the representation of words and nonwords in visual short-term memory: Evidence from human electrophysiology

Electrophysiological measures were used to investigate the contribution of lexical status on the maintenance of letter strings in visual short-term memory (VSTM). The sustained posterior contralateral negativity (SPCN), an electrophysiological marker of storage in VSTM, was measured for words and nonwords as well as scrambled letters. A smaller SPCN was found for words than for nonwords (independently of their pronounceability), indicating that lexical status influences storage in VSTM. One possibility is that words produce a smaller SPCN because they can be recoded to a form that does not require a low-level representation in VSTM. For exploratory purpose, a comparison between the nonwords and the scrambled nonwords was also made. Based on previous research, the SPCN component should not be affected by the size of the region enclosing to-be-encoded objects. Surprisingly, significant differences between the SPCN for nonwords and scrambled letters conditions were found, suggesting that special encoding mechanisms may be recruited to encode word-like letter strings.     

Chronic medication does not affect hyperactive error responses in obsessive‐compulsive disorder

Patients with obsessive‐compulsive disorder (OCD) show an increased error‐related negativity (ERN), yet previous studies have not controlled for medication use, which may be important given evidence linking performance monitoring to neurotransmitter systems targeted by treatment, such as serotonin. In an examination of 19 unmedicated OCD patients, 19 medicated OCD patients, 19 medicated patient controls without OCD, and 21 unmedicated healthy controls, we found greater ERNs in OCD patients than in controls, irrespective of medication use. Severity of generalized anxiety and depression was associated with ERN amplitude in controls but not patients. These data confirm previous findings of an exaggerated error response in OCD, further showing that it cannot be attributed to medication. The absence in patients of a relationship between ERN amplitude and anxiety/depression, as was found in controls, suggests that elevated error signals in OCD may be disorder‐specific.     

Bilateral parietal and contralateral responses during maintenance of unilaterally encoded objects in visual short-term memory: Evidence from magnetoencephalography

A component of the event-related magnetic field (ERMF) response was observed in magnetoencephalographic signals recorded during the maintenance of information in visual short-term memory (VSTM). This sustained posterior contralateral magnetic (SPCM) field is likely the magnetic equivalent of the sustained posterior contralateral negativity (SPCN) found in electrophysiology. Magnetoencephalography data showed, at the sensor level, a bilateral activation over the parietal cortex that increased in amplitude for higher memory load. Others sensors, also over the parietal cortex, showed an activation pattern similar to the SPCN with higher activation for the hemisphere contralateral to the visual field from which visual information was encoded. These two activation patterns suggest that the SPCN and SPCM are generated by a network of cortical sources that includes bilateral parietal loci, likely intra-parietal/intra-occipital cortex, and contralateral parietal sources.     

阿尔茨海默病患者听觉感觉记忆缺陷的神经电生理观察分析

目的:探讨阿尔茨海默病(AD)患者的听觉感觉记忆功能状况。方法:应用事件相关电位(ERP)中的失匹配负波(MMN)的方法对26例AD患者及31位正常人检测结果进行对照研究。结果:AD组MMN潜伏期延长、波幅降低。结论:①AD患者在听觉皮质水平上信息加工有损害;②MMN能够敏感地表达听觉感觉记忆缺陷;③因检查勿需受试者主动注意的参与,对痴呆患者及检查难以合作的患者认知功能早期阶段评估可提供帮助。     

Age‐related changes in ERP correlates of visuospatial and motor processes

Although previous ERP studies have demonstrated slowing of visuospatial and motor processes with age, such studies frequently included only young and elderly participants, and lacked information about age‐related changes across the adult lifespan. The present research used a Simon task with two irrelevant dimensions (position and direction of an arrow) to study visuospatial (N2 posterior contralateral, N2pc) and motor (response‐locked lateralized readiness potential, LRP‐r) processes in young, middle‐aged, and elderly adults. The reaction time and motor execution stage (LRP‐r) increased gradually with age, while visuospatial processes (N2pc latency) were similarly delayed in the older groups. No age‐related increase in interference was observed, probably related to a delay in processing the symbolic meaning of the direction in older groups, which was consistent with age‐related differences in distributional analyses and N2pc amplitude modulations.     

Storage of feature conjunction in transient auditor memory

The purpose of this study was to determine whether feature conjunction are stored in transient auditory memory. The mismatch negativity (MMN), an event-related potential that is elicited by stimuli that differ from a series of preceding stimuli was used in this endeavour. A tone that differed from the preceding series of stimuli in the conjunction of tow of its features, both present in preceding stimuli but in different combination, was found to elicit the MMN, the data are interpreted to indicate that information about the conjunction of feature is stored in the memory.     

Electrophysiological revelations of trial history effects in a color oddball search task

In visual oddball search tasks, viewing a no‐target scene (i.e., no‐target selection trial) leads to the facilitation or delay of the search time for a target in a subsequent trial. Presumably, this selection failure leads to biasing attentional set and prioritizing stimulus features unseen in the no‐target scene. We observed attention‐related ERP components and tracked the course of attentional biasing as a function of trial history. Participants were instructed to identify color oddballs (i.e., targets) shown in varied trial sequences. The number of no‐target scenes preceding a target scene was increased from zero to two to reinforce attentional biasing, and colors presented in two successive no‐target scenes were repeated or changed to systematically bias attention to specific colors. For the no‐target scenes, the presentation of a second no‐target scene resulted in an early selection of, and sustained attention to, the changed colors (mirrored in the frontal selection positivity, the anterior N2, and the P3b). For the target scenes, the N2pc indicated an earlier allocation of attention to the targets with unseen or remotely seen colors. Inhibitory control of attention, shown in the anterior N2, was greatest when the target scene was followed by repeated no‐target scenes with repeated colors. Finally, search times and the P3b were influenced by both color previewing and its history. The current results demonstrate that attentional biasing can occur on a trial‐by‐trial basis and be influenced by both feature previewing and its history.     

An electrophysiological measure of visual short‐term memory capacity within and across hemifields

Recent electrophysiological research has identified a specific contralateral correlate of the contents of visual short‐term memory (VSTM). This posterior contralateral delay activity (CDA) persists during the retention period, and its amplitude is modulated by the number of items held at any one time. Here we show that, despite the contralateral nature of this activity, its amplitude is modulated by the number of objects from both hemifields. When objects from one side of the visual field are held in memory, CDA activity increased for arrays of one, two, and three objects, but stopped getting larger for arrays of four objects. However, when objects from both sides are memorized at the same time, CDA activity reached its asymptotic limit for arrays of two objects per side. These results suggest that, in spite of being contralaterally organized, VSTM is limited by the number of objects from both hemifields.     

Aiming for the bull's eye: Preparing for throwing investigated with event-related brain potentials

We explored the feasibility of investigating complex goal-directed actions with event-related brain potentials by studying the aiming phase of throwing. A virtual reality environment was set up, allowing aimed throws at distant targets, with participants standing upright and moving relatively unrestrained. After a separate practice session, the contingent negative variation (CNV) was measured during preparation for a simple button release, unaimed throws, and aimed throws at targets of two levels of difficulty. Consistent with expectations, CNV amplitude was larger for all throwing conditions compared to button release. It further increased with task difficulty in the aimed throwing conditions, reflecting the increasing motor programming demands for more difficult goal-directed actions. Therefore, investigating throwing as an instance of complex goal-directed action with ERPs is feasible, opening interesting perspectives for future research.     

Multiple time scales of adaptation in the auditory system as revealed by human evoked potentials

Single neurons in the primary auditory cortex of the cat show faster adaptation time constants to short- than long-term stimulus history. This ability to encode the complex past auditory stimulation in multiple time scales would enable the auditory system to generate expectations of the incoming stimuli. Here, we tested whether large neural populations exhibit this ability as well, by recording human auditory evoked potentials (AEP) to pure tones in a sequence embedding short- and long-term aspects of stimulus history. Our results yielded dynamic amplitude modulations of the P2 AEP to stimulus repetition spanning from milliseconds to tens of seconds concurrently, as well as amplitude modulations of the mismatch negativity AEP to regularity violations. A simple linear model of expectancy accounting for both short- and long-term stimulus history described our results, paralleling the behavior of neurons in the primary auditory cortex.     

Conditions for view invariance in the neural response to visual symmetry

Symmetry detection is slow when patterns are distorted by perspective, perhaps due to a time‐consuming normalization process, or because discrimination relies on remaining weaker regularities in the retinal image. Participants viewed symmetrical or random dot patterns, either in a frontoparallel or slanted plane (±50°). One group performed a color discrimination task, while another performed a regularity discrimination task. We measured a symmetry‐related event‐related potential (ERP), beginning around 300 ms. During color discrimination, the ERP was reduced for slanted patterns, indexing only the remaining retinal structure. During regularity discrimination, the same ERP was view invariant, and identical for frontoparallel or slanted presentation. We conclude that normalization occurs rapidly during active symmetry discrimination, while symmetry‐sensitive networks respond only to regularity in the retinal image when people are attending to other features.     

Electrophysiological correlates of speech perception mechanisms and individual differences in second language attainment

In an increasingly globalized world mastering a second language (L2) provides a clear advantage. However, after early childhood, not everyone can easily learn a foreign language. The present study explored whether the large variability found in L2 attainment in the normal population, not diagnosed as learning disabled, is related to preattentive speech perception abilities. Using event‐related potentials (ERPs) we examined the mismatch negativity, P3a, and the late discriminative negativity (MMN‐P3a‐LDN) complex, which served as an index for preattentive foreign phonological contrast discrimination abilities. Our results show that, compared to unsuccessful L2 learners, successful L2 learners had shorter latencies of the MMN and P3a components and higher amplitudes of the LDN component. These results suggest that unsuccessful L2 learners have a deficient speech perception mechanism.     

Age-related changes in the impact of contextual strength on multiple aspects of sentence comprehension

Contextual information influences multiple aspects of language comprehension extended over time. To determine how age-related changes impact normal comprehension, effects of contextual strength were examined with event-related potentials. Increased contextual constraint facilitated semantic processing (reduced N400s). Effects were smaller and delayed for older adults, and sensitivity to contextual information was diminished for weak contexts. Both groups elicited a later left-lateralized frontal negativity associated with reinterpretation of context when multiple interpretations of a sentence were likely. Older adults evidenced the frontal negativity over a wider range of constraint. The change in the use of contextual information across age is attributed to decreased reliance on predictive processing for older adults. Thus, age-related changes in comprehension lead to differential engagement of processing resources over time for older adults.     

Electrophysiological correlates of threat processing in spider phobics

The electrocortical correlates of the processing of feared/fear-relevant and neutral stimuli were investigated in a pictorial emotional Stroop paradigm with spider phobic, social phobic, and nonphobic subjects. Subjects identified either the color of red or blue pictures of spiders, birds, or flowers (emotional Stroop task) or the object itself (identification task) by pressing different buttons. No emotional Stroop interference was found for spider phobic subjects when identifying the color of spiders as opposed to neutral stimuli. However, in the object identification task, spider phobic subjects identified spiders significantly faster than birds or flowers. Parietal P300 and P400 amplitudes were enhanced independent of task in spider phobic but not in nonphobic subjects when viewing pictures of spiders, which is consistent with previous studies showing that highly unpleasant and arousing pictures affect parietal late positive potentials.     

Identifying concealment‐related responses in the concealed information test

The concealed information test (CIT) assesses an examinee's recognition of a crime‐relevant item using physiological measures. However, a guilty examinee not only recognizes the crime‐relevant item but also conceals the recognition intentionally. In this study, we attempted to identify the effect of concealing the recognition on event‐related potentials and autonomic responses. After committing a mock theft of two items, 30 participants received two CITs: one for an item that they had to conceal, and the other for an item that they had disclosed. N2, P3, heart rate, skin conductance, and cutaneous blood flow differed between crime‐relevant and irrelevant items in both CITs. In contrast, late positive potential and respiration differed between crime‐relevant and irrelevant items only when the examinee needed to conceal. The former measures appear to be related to orienting process, whereas the latter to controlled process related to concealment.     

Linguistic multifeature MMN paradigm for extensive recording of auditory discrimination profiles

We studied whether a multifeature mismatch negativity (MMN) paradigm using naturally produced speech stimuli is feasible for studies of auditory discrimination accuracy of adult participants. A naturally produced trisyllabic pseudoword was used in the paradigm, and MMNs were recorded to changes that were acoustic (changes in fundamental frequency or intensity) or potentially phonological (changes in vowel identity or vowel duration). All the different changes were presented in three different word segments (initial, middle, or final syllable). All changes elicited an MMN response, but the vowel duration change elicited a different response pattern than the other deviant types. Changes in vowel duration and identity also had an effect on MMN lateralization. Our results show that assessing speech sound discrimination of several features in word context is possible in a short recording time (30 min) with the multifeature paradigm.     

Brain Potentials Related to Stages of Sentence Verification

Subjects were shown the terms of simple sentences in sequence (e.g., “A sparrow / is not / a vehicle”) and manually indicated whether the sentence was true or false. When the sentence form was affirmative (i.e., “X is a Y”), false sentences produced scalp potentials that were significantly more negative than those for true sentences, in the region of about 250 to 450 msec following presentation of the sentence object. In contrast, when the sentence form was negative (i.e., “X is not a Y”), it was the true statements that were associated with the ERP negativity. Since both the false-affirmative and the true-negative sentences consist of “mismatched” subject and object terms (e.g., sparrow / vehicle), it was concluded that the negativity in the potentials reflected a semantic mismatch between terms at a preliminary stage of sentence comprehension, rather than the falseness of the sentence taken as a whole. Similarities between the present effects of semantic mismatches and the N400 associated with incongruous sentences (Kutas & Hillyard, 1980) are discussed. The pattern of response latencies and of ERPs taken together supported a model of sentence comprehension in which negatives are dealt with only after the proposition to be negated is understood.     

Electrophysiological correlates of category induction: PSW amplitude as an index of identifying shared attributes

Event-related potentials (ERPs) were recorded from 15 healthy adults while they performed a category induction task. Two geometric figures characterized by three dimensions (color, shape, and stripe orientation) were presented simultaneously to subjects who were asked to identify their shared attributes. Pairs of figures sharing common attributes composed the category induction condition and pairs of identical figures composed the non-induction condition. It was hypothesized that non-induction only involves abstracting shared attributes from one stimulus, but category induction involves identifying shared attributes by comparing the two stimuli. The ERP waves elicited by induction and non-induction did not differ on N1, P2 and P3b components, but larger frontal N2 and smaller central-parietal PSW components were elicited by category induction. These results suggest that the processing of category induction is reflected in the PSW 400-650 ms post-stimulus.