| Decision making is a process that gathering information from sensory system and then forming priority selection, selection, motor execution and evaluation. Because of its universality and importance in human life, it has received extensive attention. Both the motor preparation and the motor execution are described as the two important parts of decision making process. And Lateralized Readiness Potential (LRP), a component of event-related potential (ERP), is closely related to these two parts. Therefore study on the decision making mechanism of LRP provides a new method to study the process of decision making. This paper utilizes the random dot motion detection task, and manipulates the proportion of coherently moving dot to control the stimulus difficulty level. And we acquires the brain signal and behavioral data from ten subjects. Then we study the process of decision making by studying the influence of difference stimulus difficulty levels on LRP.First we analyzed the brain signal. The average technique and subtract-average method were used to obtain the LRP waveform, and segment regression method was used to compute the onset of response-locked LRP. The result shows that the interval between the onset of LRP the response time increase with the increasing of the difficulty level. Thus, the interval can be regarded as an index of task difficulty. But the amplitude of LRP didn’t appear any relationship with task difficulty. It reflects that the task difficulty didn’t show any effects on the allocation of motion resources.Meanwhile we use the single-trial analysis to analyze the brain signal and find that the recognizability of task difficulty and motor direction increase with the time goes by. And the increasing of recognizability reflects the process of evidence accumulation, so as the more evidence accumulate, the better classification performance it makes. It is concluded that the evidence accumulated began about 230ms after the stimulus presentation by comparing two kinds of recognition task. This time point is a dividing point that divides the stimulus-locked LRP into two parts. The early part reflects the phase of evidence sensory and moving limbs selection, while the late part reflects the process of evidence accumulation.Second, this paper analyzed the behavioral data. And in order to establish the relationship between the performance and the mental process, we uses the diffusion model to fit the behavioral data, and then use the fitting parameter to interpret the relationship. The behavioral data analysis and drift-diffusion model parameters results indicated that the variation of the reaction time (r=-0.173) and the accuracy (r= 0.602)is significant for different difficulty levels, and the correlation between the drift rate and the difficulty levels is also significant (r=-0.463, p= 0.01<0.05) while the non-decision time doesn’t show any relationship with task difficulty. In combination with the LRP results, we conclude that the interval between the onset of response-locked LRP and the response time reflects the decision phase.In summary, this paper combined the LRP waveform analysis, the single-trial analysis and the behavior data analysis for the first time to study the decision making mechanism of LRP and use the results to analyze the mechanism of decision making process. We find that the LRP waveform reflects the decision making process. This study provides a new method for studying the perceptual decision making process. |
