Xiaohua Cao

Left-lateralized early neurophysiological response for Chinese characters in young primary school children

Adult readers consistently show an enhanced early event-related potential (ERP) response, N170, for visual words compared with other stimuli at left posterior electrodes. Developmental studies with words in alphabetic languages showed that this neurophysiological specialization for print develops rapidly from 6 to 10-years of age and becomes established around 10-11 years of age. Here we report for the first time the development of the word-related N170 in Chinese children learning to read Chinese, a logographic writing system radically different from alphabetic scripts in visual and linguistic features. We recorded ERP responses elicited by Chinese characters and line drawings of common objects in three groups of primary school children at 7, 9, and 11 years of age as well as college students. Results showed that the amplitude of N170 evoked by Chinese characters in the 7-year-old group was significantly larger than that in the 11-year-old group and the adult readers. Remarkably, all four age groups - even the youngest group - showed an increased and left-lateralized N170 response for Chinese characters, as compared with line drawings, suggesting that a relatively specialized mechanism for processing Chinese characters is already emergent by as early as 7 years of age. Our results, combined with studies of non-Chinese child readers suggest that the developmental pattern of word-related N170 is highly similar across different scripts, possibly reflecting increased visual processing expertise that children acquire through everyday reading.

Selectivity of N170 in the left hemisphere as an electrophysiological marker for expertise in reading Chinese

ObjectiveThe left-lateralized N170, an event-related potential component consistently shown in response to alphabetic words, is a robust electrophysiological marker for reading expertise in an alphabetic language. In contrast, such a marker is lacking for expertise in reading Chinese, because the existing results about the lateralization of N170 for Chinese characters are mixed, reflecting complicated factors such as top-down modulation that contribute to the relative magnitudes of N170 in the left and right hemispheres. The present study aimed to explore a potential electrophysiological marker for reading expertise in Chinese with minimal top-down influence.MethodsWe recorded N170 responses to Chinese characters and three kinds of control stimuli in a content-irrelevant task, minimizing potential top-down effects.ResultsDirect comparison of the N170 amplitude in response to Chinese characters between the hemispheres showed a marginally significant left-lateralization effect. However, detailed analyses of N170 in each hemisphere revealed a more robust pattern of left-lateralization — the N170 in the left but not the right hemisphere differentiated Chinese characters from control stimuli.ConclusionThese results suggest that the selectivity of N170 (a greater N170 in response to Chinese characters than to control stimuli) within the left hemisphere rather than the hemispheric difference of N170 with regard to Chinese characters is an electrophysiological marker for expertise in reading Chinese.

The overlap of neural selectivity between faces and words: evidences from the N170 adaptation effect

Abstract Faces and words both evoke an N170, a strong electrophysiological response that is often used as a marker for the early stages of expert pattern perception. We examine the relationship of neural selectivity between faces and words by using a novel application of cross-category adaptation to the N170. We report a strong asymmetry between N170 adaptation induced by faces and by words. This is the first electrophysiological result showing that neural selectivity to faces encompasses neural selectivity to words and suggests that the N170 response to faces constitutes a neural marker for versatile representations of familiar visual patterns.

N170 adaptation effect for repeated faces and words

Using ERP adaptation paradigms, studies have shown that the N170 adaptation effect is a stable phenomenon for both faces and words. However, the N170 adaptation effect for repeated identity remains unclear, so we have addressed this with two experiments. In Experiment 1, we investigated the face-related N170 repeated adaptation effect in a short interstimulus interval (ISI) and found that the N170 response elicited by faces was smaller when preceded by a same face adaptor than by another face adaptor. Experiment 2 addressed whether this repeated N170 adaptation effect generalizes to words. For the first time, the results indicated that the N170 response elicited by words was larger with a different word as an adaptor relative to the same word as an adaptor. Our results demonstrate that the face-related N170 response is sensitive to visual face features and extend the characteristics of N170 with the sensitivity to repeated items to other familiar objects of expertise (i.e. words). The results also suggest that there are some common characteristics between faces and words in the early perceptual processing.

The spatial distribution of inhibition of return revisited: No difference found between manual and saccadic responses

Inhibition of return (IOR) commonly refers to the effect of prolonged response times to targets at previously attended locations. It is a well-documented fact that IOR is not restricted to previously attended locations, but rather has a spatial gradient. Based on a myriad of manual/saccadic dissociations, many researchers now believe that there are at least two forms of IOR completely dissociable on the basis of response type. The present study evaluated whether these two forms of IOR are encoded in similar representations of space. Across a range of conditions, there was little indication that the two forms could be differentiated on the basis of their spatial distributions. Furthermore, the present study also found that the gradient of IOR was steepest for cues appearing nearest fixation.

Separate Capacities for Storing Different Features in Visual Working Memory.

Recent empirical and theoretical work suggests that visual features such as color and orientation can be stored or retrieved independently in visual working memory (VWM), even in cases when they belong to the same object. Yet it remains unclear whether different feature dimensions have their own capacity limits, or whether they compete for shared but limited resources in VWM. In 3 experiments, participants memorized arrays of dual-feature objects, for which the number of feature values was fixed on one feature dimension and was varied on the other feature dimension. The results show that memory performance on the fixed dimension was not affected by the number of to-be-stored feature values on the other. These findings provide converging evidence that visual features can be encoded and stored separately in VWM if the task requires it, with each having its own capacity limit and little cross-dimensional interference.

The commonality between the perceptual adaptation mechanisms involved in processing faces and nonface objects of expertise

OBJECTIVE The authors designed 2 experiments to examine the commonality of the N170 component involved in processing faces and nonface objects of expertise. METHOD In Experiment 1, to investigate the N170 adaptation effect between faces and printed language, 18 bilingual participants (7 males) were recruited, and the N170 response elicited by faces and words was recorded using a 128-channel HydroCel Geodesic Sensor Net. To address whether this asymmetrical between-category N170 adaptation effect generalizes to any object of expertise, in Experiment 2, 19 participants (9 males) were recruited by training to become Greeble experts. The N170 component elicited by faces and Greebles was recorded before and after training. RESULTS In Experiment 1, the authors found that only faces can affect the N170 response elicited by words but words cannot affect the N170 response elicited by face. In Experiment 2, both before and after training, Greeble adaptors did not affect the N170 response elicited by faces. It is important to note that after training, the faces decreased the N170 response elicited by the Greebles. CONCLUSIONS These results suggest that not only is there some commonality of N170 response elicited by face and nonface objects of expertise but also the kinds of functions associated with the N170 neural selectivity to faces were more than that to nonface expert objects.

Location-based effects underlie feature conjunction benefits in visual working memory

Studies of visual working memory (VWM) have reported that different features belonging to the same object (conjunctions) are better retained than the same features belonging to spatially separated objects (disjunctions). This conjunction benefit has been taken as evidence for the theory that VWM representations are object-based. However, compared to separate features, conjunctions also occupy fewer locations. Here we tested the alternative hypothesis that the conjunction benefit reflects a spatial-based rather than an object-based advantage. Experiment 1 shows a clear VWM conjunction benefit for spatially laid out displays of memory items. However, when the same items were presented sequentially at one location (i.e., location was noninformative), memory performance was equivalent for conjunction and disjunction conditions. Experiment 2 shows that only when the probe carries spatial information (i.e., it matches the location of the memory item) does a conjunction benefit occur. Taken together, these results put important boundaries on object-based theories of VWM.

Rapid adaptation effect of N170 for printed words.

Faces and written words are two of the most familiar types of visual patterns with the brains selective response of N170 component in early perception. Using ERP adaptation paradigms, studies have found the N170 response is reduced when there is repeated presentation of upright faces relative to a control condition. In contrast to these well-established features of the face-related N170 adaptation effect, the characteristics of the N170 adaptation effect for printed words are less clear. The goal was to investigate the ERP adaptation effects of printed language (English words and Chinese characters) in a short ISI (200msec.) adaptation paradigm. The present study showed that both alphabetic words and non-alphabetic words could produce a rapid N170 adaptation effect. Objects of expertise (e.g. words and faces) can produce a rapid N170 adaptation effect but other objects (e.g., houses) cannot, indicating that the specific stimuli have some specific mechanisms for the rapid N170 adaptation.

Sex differences of hemispheric lateralization for faces and Chinese characters in early perceptual processing

Previous event-related potential studies showed that the N170 response is left-lateralized for words and right-lateralized for faces. Using a one-back repetition task, this study aimed to clarify sex differences in hemispheric specialization for both faces and words in early visual processing. We found that the N170 amplitude elicited by faces in males was right-lateralized, while in females it was bilateral. Interestingly, the N170 amplitude elicited by Chinese characters in males was bilateral, whereas in females it was left-lateralized. The N170 latency for faces was shorter in females than in males, whereas the N170 latency for Chinese characters was similar in females and males. The degree of lateralization of faces was significantly related to the degree of lateralization of Chinese characters in both the female and male groups. Therefore, sex differences in N170 hemispheric lateralization for faces are different from those for Chinese characters, and there are some links between the two categories of objects of expertise in early perceptual processing.