Rapid Stream Stimulation Research Articles

Brain mechanism of Chinese character processing in rapid stream stimulation

In visual masking, the visibility of a fleetingly presented visual target is disrupted by the presentation of an additional image, the mask, shortly before or after the target. Rapid stream stimulation (RSS) is a masking paradigm that is frequently used in character processing. Although neuroimaging studies have examined lexicality in terms of RSS, the mechanism underlying character masking has not been investigated. To resolve this issue, we investigated the neural basis of masking effects in lexicality using a two-way factorial design in a 3T-fMRI with masking (mask condition: masked versus unmasked) and target stimulus (character likeness: real-, pseudo-, non-characters) as factors. We found that brain activity in the left middle occipital gyrus (MOG) and lingual gyrus was strongest in the unmasked condition in RSS. Analysis of psychophysiological interactions revealed diverse patterns of functional connectivity in the two conditions, with stronger functional connectivity of the left MOG to the left fusiform gyrus and the right posterior cingulate cortex, suggesting the involvement of lexical processing of familiar characters. Together, these findings of activation and connectivity patterns indicated that masking in RSS reduced the visibility of characters by suppressing activity in the occipital cortex and reduced connectivity in both orthographical and attention networks.

Rapid stream stimulation can enhance the stimulus selectivity of early evoked responses to written characters but not faces.

The recognition potential (RP) is an early visually evoked response (~250 ms) whose magnitude is sensitive to object recognizability and related factors. The RP is often measured when objects are embedded in a rapid stream of masking stimuli (the RSS paradigm), especially in reading research. The idea is that RSS provides greater stimulus-dependent variations in RP, compared to the corresponding variations without RSS. However, this idea has never been subject to systematic evaluation. We directly test whether RSS can enhance 2 types of RP stimulus selectivity, by measuring the RP in conditions that only differ in the presence or absence of a masking stream and in the type of stimulus shown. We measure the effect of image inversion on RP for Chinese characters (experiment 1); the effect of orthographical correctness on RP for Chinese characters (experiment 3); and as a control study, the effect of image inversion on the N170 response to faces (experiment 2). To ensure a fair comparison, the earliest negative deflections (RP/N170) measured with and without RSS should at least have similar channel ranges, and topographical distributions of both amplitude and selectivity. Our first set of results clearly supports this. Our main results clearly show an increase in stimulus-selectivity for RSS over non-RSS in both of the RP (Chinese character) experiments, but no such enhancement in the N170 (face) experiment. This provides incentive for investigations into the underlying mechanisms of selectivity enhancement. Our findings may also help to explain contradictory findings between RP/N170 studies that differ only in the use of noise masks, which is sometimes treated as trivial detail in papers that do not reference the RP/RSS literature.

The influence of background music on recognition processes of Chinese characters: An ERP study

In this paper, we employed RSS (rapid stream stimulation) paradigm to study the recognition processes of Chinese characters in background music. Real Chinese characters (upright or rotated) were used as target stimuli, while pseudo-words were used as background stimuli. Subjects were required to detect real characters while listening to Mozart's Sonata K. 448 and in silence. Both behavioral results and ERP results supported that Mozart's music mainly served as a distracter in the recognition processes of real Chinese characters in the experiment. The modulation of Mozart's music on RP (recognition potential) was different across different orientations of Chinese characters; in particular, the modulation of RP elicited by upright Chinese characters was more significant, suggesting that the music factor and orientation factor interact to affect the RP component. In brief, the simultaneous playing of Mozart's music did not improve subjects’ performance in the detection of real Chinese characters.

The recognition potential and rotated Chinese characters

The recognition potential (RP), which is recorded at occipital–temporal sites 200–300 ms poststimulus onset, is an event-related potential (ERP) response to a recognizable stimulus during an object recognition task. Using the rapid stream stimulation (RSS) paradigm and a word detection task, the present study investigated the effect of word detection on RP activity by manipulating angular orientation and image version of Chinese characters. The results showed larger RP amplitude during the normal condition than during the mirror-reversed condition across angular orientations. Moreover, the RP latencies were delayed for 60°, 120°, and 180° orientations relative to the upright, and the amplitudes were larger for 0° and 60° orientations than for 120° and 180° orientations only during the normal condition. This suggests that, as mirrored by RP activity, different strategies depend on the difficulty of word recognition. More specially, piecemeal and serial processing strategy would be used when incoming information is sufficient for word recognition, whereas holistic strategy and the global analysis of categorical features would be used when a word cannot be recognized due to the degraded quality of incoming stimuli.

The recognition potential: Semantic processing or the detection of differences between stimuli?

The recognition potential is traditionally described as an electrical index elicited when subjects view a recognizable stimulus. Recent studies further show that it may be influenced by semantic processing. In this study, we investigated whether this observed influence is really produced by differences in semantic processing or whether it might be caused by the detection of differences between sequentially presented stimuli. In two different experiments, we systematically altered the type of background images presented while keeping the recognizable word constant. Analyses revealed that the same recognizable words elicited an RP with different amplitudes and latencies when viewed under different background conditions. Control stimuli, which were identical to background stimuli, did not elicit the RP. Hence, we postulate that when using the rapid stream stimulation paradigm, RP might also be influenced by the detection of differences between sequentially input stimuli. It is necessary to clarify whether RP changes are caused by the processing of the stimuli or by the detection of difference between successively input stimuli before any conclusion could be made.

ERP components reflecting stimulus identification: contrasting the recognition potential and the early repetition effect (N250r)

The recognition potential component (RP) in the event-related brain potential (ERP) appears during rapid stream stimulation and has been related to the activation of word form or word meaning. The early repetition effect (ERE/N250r) is observed in repetition priming designs and has been linked to the access to stored representations of the structure of familiar faces and names. Because of the apparent similarities in latency, topography and theoretical interpretation we compared the RP and ERE/N250r within the same rapid stream stimulation design and for the same type of stimulus material: names and faces of famous persons and names and pictures of common objects. Contrasting with RP, the ERE/N250r occurred later and differed in both scalp topography and amplitude patterns across stimulus conditions. Therefore, the ERE/N250r seems to reflect a separate and content-specific stage of information processing, following the RP, which appears to reflect domain-general processes of structural analyses.

The recognition potential during sentence presentation: stimulus probability, background stimuli, and SOA

Recognition potential (RP) is an electrical brain response that has proved its usefulness for studying semantic processing of isolated words, and appears when subjects view meaningful stimuli embedded in a stream of background images at a high rate of presentation: the rapid stream stimulation paradigm (RSS). The present technical study is aimed at testing the validity of this procedure in the study of words within sentences. For this purpose, we varied word and background probability of appearance, the number of background stimuli preceding each word, and stimulus onset asynchrony. Probability did not have significant effects on RP, but it was found that a minimum number of two background stimuli preceding each word and a high rate (250 ms) of presentation are preferable for enhancing RP amplitude. The RSS paradigm would therefore improve the visibility-and, hence, refine the analysis-of a component that can nevertheless be obtained with more standard paradigms, such as rapid serial visual presentation, devoid of interspersed background stimuli.

Electrophysiological evidence of an early effect of sentence context in reading

Recognition Potential is an electrophysiological response of the brain that is sensitive to semantic aspects of stimuli. According to its peak values (about 250 ms), Recognition Potential appears as a good candidate to reflect lexical selection processes. Consequently, Recognition Potential might be sensitive to contextual information during reading a sentence. In present study, the standard procedures to improve the visibility of Recognition Potential (Rapid Stream Stimulation paradigm) were used in a task in which sentence context was crucial. A parieto-occipital Recognition Potential was observed to peak about 264 ms after stimulus onset, followed by a centro-parietal N400 peaking at about 450 ms. Recognition Potential was affected by contextual information though, contrary to N400, presenting larger amplitude to contextually congruous words. These results support the assumption that Recognition Potential may reflect lexical selection processes, representing also evidence of context effects on ERP around 250 ms after stimulus onset during sentence reading.

The recognition potential and repetition effects

The recognition potential (RP) is an electrical brain response peaking at 250 ms that appears when subjects view meaningful stimuli. Previous RP research was conducted in experimental conditions in which repetition effects could not be totally ruled out as influencing the generation of the RP response. The present study aims to elucidate whether repetition effects affect the topography and waveform of this component. For this purpose semantically correct, orthographically correct, strings of random letters, control and background stimuli were presented to 20 subjects following the rapid stream stimulation procedure and without repetition of any test stimulus. As previously, the RP showed its maximal amplitude at the PO7 electrode. It showed sensitivity to all levels of lexical processing, its response being maximal for semantically correct stimuli, and its topographical distribution was similar for all types of stimulus. Direct statistical comparisons with the data of a previous study where repetition effects could not be disregarded were performed, confirming the similarity between the results obtained in both experiments. The neural generators of the RP were placed again, as in previous studies, within the lingual gyrus. Although repetition effects have been reported to affect other semantic-related components such as the N400, they do not seem to affect either the topography or the waveform of the RP.

Studying semantics in the brain: the rapid stream stimulation paradigm

Event-related potentials (ERPs) provide information about the temporal course of cognitive processes in the brain. They have proved to be a valuable tool in order to explore semantic aspects of word processing. However, to date, research in this field has been mostly concerned with the study of post-lexical features by means of the N400-paradigm. We introduce here the rapid stream stimulation paradigm, in which stimuli reflecting different levels of linguistic information are presented to subjects at a high rate of stimulation. The present protocol shows in detail how this paradigm can be applied. The application of the rapid stream stimulation paradigm evokes the recognition potential (RP), an ERP component that peaks at around 260 ms after stimuli onset and seems to be reflecting lexical selection processes. Results of studies that revealed the sensibility of the RP to visual-semantic aspects and the location of its neural generators within basal extrastriate areas are reported. Although some research has been conducted with the rapid stream stimulation paradigm much remains still to be done. Some of the possibilities that this paradigm offers are further discussed.

Semantic processing of open- and closed-class words: an event-related potentials study

Previous research on open- and closed-class words has revealed the existence of several differences in the processing of these types of vocabulary. In this paper the processing of open- and closed-class words was compared by means of an early electrical brain response, recognition potential (RP), which indexes semantic processing and originates from basal extrastriate areas. The effects of word frequency on closed-class words were also investigated. For these purposes, open- and closed-class words, among other stimuli, were presented by means of the rapid stream stimulation procedure. Results showed that there were no significant differences when comparing the RP evoked by open- and closed-class words in the left hemisphere. However, in the right hemisphere this situation changed: the RP evoked by open- and closed-class words did differ. Moreover, there were no differences between the RP evoked by closed-class words and pseudowords. These patterns of results suggest that the semantic processing of closed-class words shares some aspects with the processing of open-class words, despite the existence of some differences. Thus, whereas the semantic processing of open-class words recruits brain areas of both hemispheres, the semantic processing of closed-class words is left-lateralized. A second purpose of this work is to study word-frequency effects on closed-class words. Our results show the insensitivity of closed-class words to word-frequency effects.

Common basal extrastriate areas for the semantic processing of words and pictures

Objective: The recognition potential (RP) is an electrophysiological brain response which is sensitive to the semantic processing of meaningful stimuli. In this study we attempt to elucidate the topography and neural origin of the RP evoked by pictures and to compare it with the RP evoked by words.Methods: Words, pictures, Chinese characters and control stimuli were presented to 20 subjects following the rapid stream stimulation procedure. The activity was recorded using 60 cephalic electrodes.Results: We found a RP displaying its maximal amplitude at the left inferior parieto-occipital electrode (PO7) for words and at the right homologue electrode (PO8) for pictures and Chinese characters. Both the amplitude and the latency of the RP were larger in the case of words. A profile analysis indicated that the neural generators of the RP were common regardless of the type of stimulus, and a dipole analysis placed them about the lingual gyrus.Conclusions: Words and pictures share the same neural generators for the RP despite of subtle differences in lateralization. This is interpreted as an index of a multimodal semantic processing in basal extrastriate areas.

The recognition potential and word priming.

The effect of priming on the latency of the recognition potential (RP) was tested using rapid stream stimulation. Subjects detected five-letter words in a stream of nonword images. Lifting the right index finger signalled detection of a word. Rapid responses were rewarded and false alarms were penalized. Just before generating an image stream, a computer briefly displayed either the specific target word or or five-letter string that indicated the target was any one of ten previously studied words. Precise target specification was expected to produce more rapid detection than the provision of less definite information. Since the RP was thought to reflect the speed of perception, it was predicted that its latency would be less when the target word was beforehand than when less specific information was provided. The results for 10 subjects confirmed the hypothesis.

Rapid stream stimulation and the recognition potential

The “recognition potential” is an electrical response of the brain thatoccurs for recognizable, but not for non-recognizable, images. When a recognizable image evokes it, the more rostral of a pair of vertically oriented occipital electrodes reaches an initial positive peak at about 200–250 msec. Several properties distinguish this component of the evoked response from event-related potentials such as N2 or P3. A new method of stimulation was devised that evoked the recognition potential for recognizable images, but virtually no response of any king for non-recognizable images. This was accomplished by presenting images at high rates. Chinese ideographs evoked it for subjects whose native language was Chinese, but not for subjects unfamiliar with that language. This showed that the recognition potential was not caused by differences in the physical attributes of the images per se. Instead, recognizability, as defined by a subject's individual learning experience, was the important factor.