The Study Of ERP On Mental Rotation

Research on visual image in cognitive psychology consists of mental rotation and mental scanning. Ability of visual image is the essence of spatial intelligence, and individuals with high spatial ability are needed in a lot of special occupations. So research on visual image is of great importance in the selection of personnel and the evaluation of performance. Shepard and Melzler began to study on mental rotation in the 1970s. They proved the existence of mental rotation with RT and error rate by the means of behavioural study. With the coming up of variety of the brain functional image technology, the study of brain mechanism of mental rotation becomes an active area in the cognitive neuroscience. This study explored the brain mechanism of mental rotation employing the Event-Related Potential (ERP) from the angle of cognitive psychology and cognitive neuroscience.This study used the identical and mirror image letters, numbers and Chinese characters as stimulus, asked the subjects to finish the mental rotation tasks, and made a comprehensive analysis combining both the behavioural and ERP data. The experiments, data collection and data analysis were all done on the 32 channels brain evokedpotential workstation produced by the NeuroScan Corporation in America.Twenty-six normal male subjects took part in the experiments. The experiment consists of 4 parts. First, to study the change of ERP's P300 with the letter R rotated in different angles as stimulus. Second, to observe the change of P300 with the Chinese character 司 rotated in different angles as stimulus. Third, to ask the subjects to fulfill different taks according to the instruction in the claasification tasks of letters and numbers; to compare the different ERP's P300 induced by the stimulus pictures needing or not needing mental rotation. Fourth, to intervene in the different processing stages of mental rotation task according to the traditional mental rotation theories, to add vision noise to the stimulus pictures and postpone the process of mental rotation in order to study the change of P3 00.The main results are as follows:1. Stimulated by letter R s, which were rotated 0 or 360 and no matter identical or mirror image, the RT needed in judgment was the lest (identical image 431+54ms, mirror image 504+59ms); With the increase of rotation angles, RT also increased. Rotated 180, RT was the longest(identical image 624+79ms, mirror image 661+ 114ms). There was obvious linear function relationship between the rotation angles of stimulus pictures and RT. In the mental rotation process, there is apparent P300 in parietal. The amplitude becomed relatively more negative and the latency was prolonged with increasing angular disparity from the upright. The average amplitude of mirror image stimulus Pz decreased from 11.43+1.98 uV to 8.98+2.03 uV. Theaverage amplitude of mirror image stimulus Pz decreased from 10.47 + 2.36 uV to 8.63 + 1.59 uV.2. Stimulated by unbalanced Chinese characters, RT prolonged with the increase of rotation angle; 515+94ms in 0 and 698+89ms in 180 when in identical image, 515+94ms in 0 698+89 ms in 180 when in mirror image. P300's amplitude, which also became more negative with the increase of rotation angle, was 15.01+2.56 u V in 0 and 11.91+2.01uV in l80.3. In the classification task, the amplitude of P300 became more negative when the stimulus needed to be rotated. The amplitude of P300 had no significant changing when the stimulus didn't need to be rotated.4. With vision noise added to the stimulus pictures, the quality of perception decreased, the mental rotation process postponed, and the onset of the amplitude modulation was delayed.Conclusion:When image is undergoing the mental rotation process, with the different rotation angles the mental resources needed are different, which can be conformed by the change of P300. The change of P300's amplitude and latency are the electrophysiology indicator that reflects the cognitive process of mental rotation and the brain mechanism.