Sex differences in the neuroanatomy of human mirror-neuron system: a voxel-based morphometric investigation.

Females frequently perform better in empathy, interpersonal sensitivity, and emotional recognition than do males. The mirror-neuron system has been proposed to play an important role in social cognition. It remains to be clarified, however, whether the neuroanatomy underlying the human mirror neuron system exhibits sex differences. With the use of voxel-based morphometry analysis, a whole-brain unbiased technique to characterize regional cerebral volume differences in structural magnetic resonance images, concurrent with the dispositional empathy measures, we demonstrate that young adult females (n=25) had significantly larger gray matter volume in the pars opercularis and inferior parietal lobule than matched males (n=25) participants. Moreover, higher self-report scores in the emotional empathic disposition was tightly coupled with larger gray matter volume of the pars opercularis across all female and male participants (P=0.002). These results indicate that the existence of neuroanatomical sex differences in the human mirror-neuron system. They also suggest that the network of the human mirror-neuron system is strongly linked to empathy competence.

Segregation of visual selection and saccades in human frontal eye fields.

The premotor theory of attention suggests that target processing and generation of a saccade to the target are interdependent. Temporally precise transcranial magnetic stimulation (TMS) was delivered over the human frontal eye fields, the area most frequently associated with the premotor theory in association with eye movements, while subjects performed a visually instructed pro-/antisaccade task. Visual analysis and saccade preparation were clearly separated in time, as indicated by 2 distinct time points of TMS delivery that resulted in elevated saccade latencies. These results show that visual analysis and saccade preparation, although frequently enacted together, are dissociable processes.

A left-lateralized network for reading Chinese words: a 3 T fMRI study.

fMRI was used to investigate brain organization for reading in Chinese. Subjects were shown two-character Chinese words. A control task was used to eliminate the non-linguistic visual and motor confounds. Results show that naming of Chinese logographs is characterized by left-lateralized neuronal networks for the processing of orthographic, phonological, and semantic attributes. The orchestration of the middle frontal cortex, superior temporal cortex, superior parietal cortex, basal temporal area and extrastriate cortices of the left hemisphere may manifest the particularity of the central representation of simple word naming in Chinese.

Local-level and global-level form characteristics in apparent-motion correspondence.

This study addressed the "correspondence" problem of apparent-motion (AM) perception in which parts of a scene must be matched with counterparts separated in time and space. Given evidence that AM correspondence can be mediated by two distinct processes--one based on a low-level motion-detection mechanism (the Reichardt process), the other involving the tracking of objects by visual attention (the attention-based process)--the present study explored how these processes interact in the perception of apparent motion between hierarchically structured figures. In three experiments, hierarchical figures were presented in a competition motion display so that, across frames, figures were identical at either the local or the global level. In experiment 1 it was shown that AM occurred between locally identical figures. Furthermore, with the Reichardt AM component eliminated in experiments 3 and 4, no preference was obtained for either level. While evidence from previous studies that form extraction for hierarchically structured figures proceeds from the global to the local levels, the present results indicate the irrelevance of such a global precedence in AM correspondence. In addition, it is suggested that Reichardt AM correspondence between local elements constrains attention-based AM correspondence between global figures so that both components move in the same direction. It is argued that this constraining process represents an elegant means of achieving AM correspondence between objects undergoing complex transformation.

The classifier problem in Chinese aphasia.

In recent years, research on the relationship between brain organization and language processing has benefited tremendously from cross-linguistic comparisons of language disorders among different types of aphasic patients. Results from these cross-linguistic studies have shown that the same aphasic syndromes often look very different from one language to another, suggesting that language-specific knowledge is largely preserved in Broca's and Wernicke's aphasics. In this paper, Chinese aphasic patients were examined with respect to their (in)ability to use classifiers in a noun phrase. The Chinese language, in addition to its lack of verb conjugation and an absence of noun declension, is exceptional in yet another respect: articles, numerals, and other such modifiers cannot directly precede their associated nouns, there has to be an intervening morpheme called a classifier. The appropriate usage of nominal classifiers is considered to be one of the most difficult aspects of Chinese grammar. Our examination of Chinese aphasic patients revealed two essential points. First, Chinese aphasic patients experience difficulty in the production of nominal classifiers, committing a significant number of errors of omission and/or substitution. Second, two different kinds of substitution errors are observed in Broca's and Wernicke's patients, and the detailed analysis of the difference demands a rethinking of the distinction between agrammatism and paragrammatism. The result adds to a growing body of evidence suggesting that grammar is impaired in fluent as well as nonfluent aphasia.

Cerebral asymmetry in visual attention.

The traditional view of cerebral lateralization of various cognitive functions has been challenged by results from recent experimental and clinical studies. Evidence has been gathered to suggest that a seemingly unitized cognitive function can be further broken down into various processing subcomponents which are distributed across the two hemispheres. For instance, according to such a more complex conceptualization of cerebral lateralization, language is seen not as a unitary ability, but rather as a collection of syntactic, semantic, and prosodic components, with each lateralized in particular manners. In much the same way, the present study attempts to examine the cerebral lateralization patterns of the seemingly unitary visual perception process. In a visual half-field experiment, 20 normal subjects were asked to make same/different judgments to laterally presented arrays of stimuli of the same type as previously studied by Treisman and her colleagues in experiments attempting to separate the preattentive and attentive stages of visual perception. Hemispheric differences were obtained only in tasks requiring attentive processing (i.e., Treisman's glueing). Results indicate a local attentional strategy for the left hemisphere and a global attentional strategy for the right hemisphere.

Search for a common neurocognitive mechanism for language and movements.

Examination of the common properties in the three Ss (i.e., speech, script, and sign languages) of human communication suggests that duality of patterning is the key feature in the development of these communication systems. This feature is in essence a sequential strategy that serves as an interface between the increasing number of messages and the limited capacity of our signal production-reception systems. It is argued that since the left hemisphere has a much finer temporal resolution than the right hemisphere, both language and movement systems might have made use of this advantage provided by the left hemisphere to fulfill the requirements of sequential strategy in their early evolution.

Role of cerebral hemispheric processing in the visual half-field stimulus-response compatibility effect.

Two experiments were conducted to test theories of the stimulus-response (S-R) compatibility effect. Stimuli presented above and below a fixation point in the left and right visual field signaled choice responses in the midsagittal plane. Even though the duration of stimulus presentation in Experiment 1 was sufficiently brief, such that the possibility of eye movements was precluded, a visual half-field S-R compatibility effect was still obtained. That such an effect is found when it can be adequately specified to which hemisphere stimulus information is presented suggests that an explanation in terms of cerebral laterality factors be considered. The second experiment employed arbitrary symbols to represent the spatial property of stimuli used in prior experiments, and a similar pattern of results was obtained. These results are discussed in terms of a functional view of cerebral organization.

Meaning specificity in sentence processing.

Two experiments were conducted to test the principle of encoding specificity in sentence recognition when the target sentence was embedded in a meaningful discourse. The results indicate that change in meaning context resulted in significantly less recognition of the target sentences while change in sentence form and the target-test interval had no significant effects. The findings were discussed within the framework of a semantic interpretation of the encoding specificity principle.

A precedence effect in the processing of verbal information.

When a brief sound is monitored in a sound-reverberating room, it is immediately followed by numerous echoes bounced off the walls and ceiling. Only the first sound to arrive at the ears appears to be used in its localization. This is generally referred to as the precedence effect. If the processing of verbal information is seen as a reverberating system (after Hebb) and rehearsal as the manifestation of the echoes, then an analogous precedence effect can be empirically demonstrated. Such an analogy not only helps explain previously uninterpretable data but also generates a very unique prediction that was confirmed by experimental data. The theoretical implications of the analogy are also discussed.