Chunyan Guo

Electrophysiological Correlates of Visual Affective Priming

The present study used event-related potentials (ERPs) to investigate the underlying neural mechanisms of visual affective priming. Eighteen young native English-speakers (6 males, 12 females) participated in the study. Two sets of 720 prime-target pairs (240 affectively congruent, 240 affectively incongruent, and 240 neutral) used either words or pictures as primes and only words as targets. ERPs were recorded from 64 scalp electrodes while participants pressed either Happy or Sad buttons to indicate target pleasantness. The response time (RT) results confirmed an affective priming effect, with faster responses to affectively congruent trials (659 ms) than affectively incongruent trials (690 ms). Affectively incongruent trials had larger and more negative N200 activation than those to neutral trials. Importantly, a delayed N400 for word prime-target pairs matched the RT results with larger negative amplitudes for incongruent than congruent pairs. This finding suggests that the N400 component is not only sensitive to semantic mismatches, but is also sensitive to affective mismatches for word prime-target pairs.

Age effects on brain activity during repetition priming of targets and distracters

The effects of age on repetition priming and how such differences were related to intentional learning and working memory status were examined. Fourteen older (age 65-75) and 14 younger (age 18-28) healthy adults performed a modified delayed match-to-sample task consisting of a target object held in mind followed by nine test objects. Sixty four-channel EEGs were recorded as participants indicated whether each test object was the same or different from the target object. Half of all target and distractor objects were intentionally studied prior to the task, and both target and distractor objects were repeatedly presented up to four times in each trial. Although both age groups showed repetition priming effects, speed increases due to repetition were more enhanced for elderly. ERP repetition effects for both younger and older adults were indexed via early (200-550) and late (550-850 ms) components. The early repetition effect was affected by whether a distractor was previously studied or not for younger but not for older adults. In contrast, the late repetition effect was not affected by prior intentional learning, and a marginal age effect suggested that repetitions of distractors likely affected older and younger adults differently. These findings suggest that at least two distinguishable repetition mechanisms differentially affect adult aging.

Distinct neural mechanisms for repetition effects of visual objects.

Repetition of visually common objects was examined in relation to prior intentional learning and memory status using a delayed match-to-sample task in humans. Both response time and two temporally separate event-related potential (ERP) components indexed repetition. The early repetition effect ( approximately 200-550 ms) evoked more ERP responses for repeated visual objects, and was diminished by prior intentional learning (old/new) or being maintained in working memory (targets/distracters). In contrast, the late repetition effect (after approximately 550 ms) evoked reduced ERP activation for repeated items, and was not affected by prior learning or working memory status. Our source localization results indicate that the late and posterior repetition effect in visual cortex is consistent with repetition suppression results reported in monkey physiology and human fMRI studies. Meanwhile, the early and anterior repetition effect, in temporal pole and frontal cortices, is modulated by explicit memory mechanisms.

Brain potentials distinguish new and studied objects during working memory

We investigated brain responses to matching versus nonmatching objects in working memory (WM) with a modified delayed match‐to‐sample task using event‐related potentials (ERPs). In addition, ERP correlates of new items (new matches/new nonmatches) and previously studied items (studied matches/studied nonmatches) were examined in the WM task. Half of the common visual objects were initially studied until 95% accuracy was attained and half were new. Each memory trial began with the presentation of a sample object followed by nine test objects. Participants indicated whether each test item was the same as the object held in mind (i.e., match) or a nonmatch. Compared to studied matches, new matches evoked activity that was 50 ms earlier and largest at frontal sites. In contrast, P3 activity associated with studied nonmatches was larger than for new nonmatches at mostly posterior sites, which parallels previously reported old–new ERP effects. The ERP source analysis further confirms that the cortical mechanisms underlying matching objects and rejecting irrelevant objects during the task are both temporally and spatially distinct. Moreover, our current findings suggest that prior learning affects brain responses to matching visual items during a WM task. Hum Brain Mapp 2008.

Brain responses to repeated visual experience among low and high sensation seekers: role of boredom susceptibility

To better understand individual differences in sensation seeking and its components, including boredom susceptibility and experience seeking, we examined brain responses of high and low sensation seekers during repeated visual experience. Individuals scoring in the top and bottom quartiles from a college-aged population on the Brief Sensation-Seeking Scale (BSSS) participated in an event-related potentials (ERPs) experiment. Line drawings of common objects were randomly intermixed and presented 1-3 times. Sixty-four channel ERP responses were recorded while participants classified items as man-made or not man-made in a repetition priming task. The two groups showed different ERP responses at frontal electrode sites after seeing a visual stimulus for 400-800 ms. The frontal late positive components (LPC) showed different habituation of ERP responses to new and studied repeated objects between high and low sensation seekers. Source localization analysis (LORETA) indicated that during visual stimulus adaptation the ventral pre-frontal cortex showed lack of frontal involvement among high sensation seekers. Furthermore, frontal LPC latencies during repeated visual exposure correlated with boredom susceptibility and experience seeking subscales. The distinct profiles of brain responses to repeated visual experience in high and low sensation seekers provide evidence that individual differences in neural adaptation can be linked to personality dimensions.

The time course of spoken word recognition in Mandarin Chinese: A unimodal ERP study

In the present study, two experiments were carried out to investigate the time course of spoken word recognition in Mandarin Chinese using both event-related potentials (ERPs) and behavioral measures. To address the hypothesis that there is an early phonological processing stage independent of semantics during spoken word recognition, a unimodal word-matching paradigm was employed, in which both prime and target words were presented auditorily. Experiment 1 manipulated the phonological relations between disyllabic primes and targets, and found an enhanced P2 (200-270 ms post-target onset) as well as a smaller early N400 to word-initial phonological mismatches over fronto-central scalp sites. Experiment 2 manipulated both phonological and semantic relations between monosyllabic primes and targets, and replicated the phonological mismatch-associated P2, which was not modulated by semantic relations. Overall, these results suggest that P2 is a sensitive electrophysiological index of early phonological processing independent of semantics in Mandarin Chinese spoken word recognition.

Neural basis for successful encoding and retrieval of prospective memory

Prospective memory (PM) refers to memory for future intentions. Difference due to memory (Dm effect) is the difference in neural activity related to stimuli that were subsequently remembered or forgotten. Using event-related potentials (ERPs), the present study investigated the Dm effect for PM using a subsequent task-switching paradigm. The results showed that a Dm effect of ERP P150 was more positive-going for later PM hit trials than for later PM forgotten trials during 100–200 ms. This Dm effect may reflect the process for the production of future intention or the process for attention. Consistent with previously reported Dm effects of other types of memory, we found that the fbN2 (250–280 ms) and late positivity component (400–700 ms) were stronger in later PM hit trials than in forgotten trials. The fbN2 was evoked by Chinese characters. The late positivity component was related to the precise encoding process. In conclusion, because of the early P150, PM encoding appears to be somewhat different from previously identified Dm effects. However, further research is needed. Our findings reveal that Dm effects of PM share similar characteristics with known Dm effects of other types of episodic memory after the very early stage of neural processing.

Task modulation of disyllabic spoken word recognition in Mandarin Chinese: a unimodal ERP study.

Using unimodal auditory tasks of word-matching and meaning-matching, this study investigated how the phonological and semantic processes in Chinese disyllabic spoken word recognition are modulated by top-down mechanism induced by experimental tasks. Both semantic similarity and word-initial phonological similarity between the primes and targets were manipulated. Results showed that at early stage of recognition (~150–250u2009ms), an enhanced P2 was elicited by the word-initial phonological mismatch in both tasks. In ~300–500u2009ms, a fronto-central negative component was elicited by word-initial phonological similarities in the word-matching task, while a parietal negativity was elicited by semantically unrelated primes in the meaning-matching task, indicating that both the semantic and phonological processes can be involved in this time window, depending on the task requirements. In the late stage (~500–700u2009ms), a centro-parietal Late N400 was elicited in both tasks, but with a larger effect in the meaning-matching task than in the word-matching task. This finding suggests that the semantic representation of the spoken words can be activated automatically in the late stage of recognition, even when semantic processing is not required. However, the magnitude of the semantic activation is modulated by task requirements.

Attention and available long-term memory in an activation-based model

The influence of attention on memorizing related items and on available long-term memory (ALTM) was explored, showing that N400 of no-memory items was more negative than that of the memory item. The results of the category comparison task indicated that information processing under attention-driven in WM determined the availability of related long-term memory, i.e., specific content, which was formerly concerned or ignored, yielding different indirect semantic priming effects. These indicate that the orientation of conceptual attention leads the related representations of LTM to diverse activation patterns, supporting the activation-based model.

Erratum to “distinct neural mechanisms for repetition effects of visual objects” : [Neuroscience 149 (2007) 747–759]

ig. 3. Difference waves for old/new and repetition effects of distracters. (A) ERP old/new difference waves (studied minus new) for distracters at Pz. B) Early ERP repetition effect (repeated minus initial presentations) for new distracters at Cz