[Differential visual attention scales directed by location versus semantic cue].

OBJECTIVE: To compare the cortical mechanisms associated with visual spatial attention directed by location cues and Chinese character cues. METHOD: Eleven healthy adults (mean age=19) with normal vision served as the subjects. In experiment I, the cue was a circle with black solid line. There were three cue sizes: small, medium and large. In experiment II, three black concentric circles were presented as background, their diameters were the same as the three cues used in experiment I. The cue was one of three Chinese characters small, medium or large respectively. The task of the subjects was to discriminate the target's orientation. RESULT: RT in experiment II was longer with short ISI. The anterosuperior N1 amplitude elicited by the cue in experiment II was larger than that in experiment I. The inferoposterior P1 latency in experiment II was longer than that in experiment I. Comparing the target evoked ERP, the inferoposterior P1 and N1, latency of experiment II was longer than that in experiment I, the inferoposterior P2 amplitude in experiment II was larger than that in experiment I. CONCLUSION: The processing of Chinese cue takes place at higher level functional brain regions compared to processing of location cue. The later requires more resource in the earlier stage of cue process and less in the subsequent stage of the task.

[Brain processing component during face cognition--N170 revealed by event-related potentials].

Objective. To observe features of early component N170 during face recognition. Method. Scalp distribution, amplitude, and latency of N170 was recorded during face recognition tasks in 16 normal subjects. Result. N170 was elicited by the face stimuli in only half of the subjects and the amplitude was modulated by cognitive tasks. Conclusion. N170 reflects not only face structure encoding unit but also direct visual processing unit. Whether N170 reflects the specialty in face recognition needs further study. The latency of N170 showed left hemisphere dominance and the amplitude showed right hemisphere dominance, indicating that it is not pure right hemisphere dominance in face recognition.

[The mechanism of gain in scale of visual attention].

Objective. To compare the cortical mechanisms associated with the visual spatial attention directed by fixed location cues. Method. The subjects were 12 healthy right-handed young volunteers. The visual stimuli were presented with the sequence as: background-cue-target. The cue was a black circle varied in three different sizes randomly. The foci of the circles were always at the center of the screen. The task of the subjects was to search the target within the cue circle and discriminate its orientation. Electroencephalogram (EEG) was recorded from 128 scalp sites. Result. The reaction time (RT) to the targets in the same location shortened when the cue size enlarged. The target evoked P1 and N1 components were not affected by the attentive region size, while the amplitudes of the inferoposterior P2 and anterosuperior N2 enlarged when the attentive region size enlarged. Conclusion. 1) The P1 and N1 components under visual attention were related to the spatial location processes mainly. 2) Cue-evoked P2 and N2 components were related to the size of attentive region. 3) The processes of spatial location information were earlier than attentive scale information, which supported the theory that spatial selection is a prerequisite for correct processes of visual object information.