刺激的知觉辨认难度与大脑两半球间的分布式加工

采用半视野速示术将标准刺激在中间视野呈现，比较刺激以不同偏心视角（3.5°，5°和6.5°）在左或右视野同时呈现，以检查不同偏心视角引起比较刺激知觉辨认难度的改变对汉字大写数字奇－偶概念同/异判断任务在大脑两半球间分布式加工的影响。结果显示：随偏心视角的增大正确反应时和错误百分数均显著提高；三种视角条件下左右手的正确反应时均有明显的右视野（左半球）优势；3.5°视角右视野（左半球）呈现时右手反应明显快于左手，5°视角右视野（左半球）与左视野（右半球）呈现时均为右手反应明显快于左手，6.5°视角右视野（左半球）与左视野（右半球）呈现时均为左手反应明显快于右手。这些结果提示：本研究条件下只有比较刺激在6.5°偏心视角呈现时刺激和反应可能出现大脑两半球间分布式加工，3.5°和5°视角呈现时可能为左半球单独加工。6.5°视角刺激呈现的分布加工明显由于大视角呈现时比较刺激辨认难度与注意要求的提高所致。

TASK DIFFICULTY IN PERCEPTUAL IDENTIFICATION OF STIMULUS AND DISTRIBUTING PROCESSING ACROSS TWO HEMISPHERES

Tachistoscopic visual half-field test was used to examine effects of an early perceptual factor of stimuli on the distributing processing across two hemispheres. An odd-even conceptual decision task on pairs of numerals in capitals of Chinese characters was given to subjects involving three different eccentricities( 3.5°, 5° and 6.5° ) of comparative numerals in order to vary the perceptual processing demands of the stimuli. The results showed that the reaction times were slower and the percentage of errors higher while increasing eccentricity of the comparative stimuli. There was a superiority of correct reaction speed for RVF(LH) presentation, regardless of eccentricities and responding hands. A comparasion of the left and the right hand indicated that response with the left hand was more rapid than with the right hand at 6.5°, and response with the right hand was more rapid than with the left hand at 3.5° and 5°. These results suggest that the stimulus and response processing for this task tend to be distributed across the two hemispheres at 6.5°, and operated at 3.5° and 5° by the left hemisphere independently. The effect of distributing processing appeared at 6.5° could result from more difficult perceptual and attentional demands of the comparative stimuli.