| Spatial-Numerical Association of Response Codes effect(SNARC effect)refers to the tendency during number processing that the left hand responds faster to small numbers,and the right hand responds faster to large numbers.Previous studies with the help of free-choice paradigm have found that the magnitude of numbers not only affects the speed of the participants' response,but also affects their choice of response direction such as eye movement,button pressing and turning around.However,the numerical stimuli in previous studies are mainly presented intuitively,and the random number generation task is seldom combined with the free-choice paradigm.Therefore,the purpose of this study is to investigate whether the magnitude of number still affects the response selection without directly presented,and to explore the specific generation stage of this effect through EEG.Moreover,we want to know whether there is a difference in brain processing between numbers seen and imagined.The experimental tasks in this study consists of free selection,parity and magnitude judgment.In the free selection task,the participants need to press “F” or “J” according to their own will to response to the number presented on the screen.When a question mark appears on the screen,it means they should press the button after generating a number in their own mind.The numbers seen and imagined were generated within the range of 1,2,8,9.Then the participants were asked to make parity and magnitude judgment on the numbers they saw or imagined.Because the subjects were not required to report the number imagined during the experiment,the results of parity and magnitude judgment enabled us to infer which number generated by subjects after the experiment,so only the subjects who reach the specified accuracy rate(?80%)will be adopted.In addition,in order to distinguish the response of the subjects from their inherent response tendency or the influence of numerical magnitude,symbols(#,&)were added as neutral stimuli in the free selection task.This study consists of two experiments.Experiment 1 adopted the experimental design of 4(stimulus presentation time: 1000 ms,1200ms,1400 ms,1600ms)×2(stimulus type: number seen,number imagined)×2(number magnitude: small,large).It was found that only when the stimulus was presented at 1600 ms did both the numbers seen and imagined exhibit the SNARC effect: The left hand responds more to small numbers,and the right hand responds more to large numbers.Experiment 2 used the same procedure as experiment 1,and adopted the experimental design of 2(stimulus type: number seen,number imagined)×2(number magnitude: small,large)with 1600 ms as stimulus presentation time to conduct EEG research.The behavior results were consistent with the experiment 1,that is,we found the congruency effect(congruent:left-small,right-large;incongruent:left-large,right-sm all)of numbers seen and imagined.The EEG results showed that the SNARC effect of the numbers seen appeared in components P1 of the parietal-occipital and N2-P3 of the frontal and parietal areas,while the SNARC effect of the numbers imagined only occurred in the N1 component of the parietal-occipital region.Specifically,congruent keying elicited more positive P1 in stimulus presentation stage and incongruent keying elicited more positive N2-P3 in response selection stage for the number seen,while incongruent keying produced more negative N1 for the number imagined.In addition,the average amplitude induced by the number seen and imagined is different in bilateral hemispheres.For the number seen,N2 in the frontal lobe showed that the amplitude of the left hemisphere was more negative than that of the right hemisphere,and P3 in the frontal lobe showed that the amplitude of the right hemisphere was more positive than the left hemisphere.For the number imagined,parietal-occipital P1 and frontal P3 showed that the left hemisphere was more positive than the right hemisphere,and frontal N2 showed that the right hemisphere was more negative than the left hemisphere.In terms of latency,both P1 and P2 in parietal-occipital showed that the number seen started earlier than the number imagined in the left hemisphere,while the number imagined started earlier than the number seen in the right hemisphere.However,in the N2 and P3 components of the frontal lobe,the left and right hemispheres both showed that the number imagined started earlier than the number seen.The results of this study show that :(1)Even if there's not number-related information input to sensory perception,the connection between number and space still exists and is manifested by its influence on response selection;(2)No matter for the number seen or imagined,the spatial-numerical association has affected the choice of the participants' response in the perceptual representation stage.The SNARC effect of both the number seen and imagined occurred in the early perceptual coding stage,and the SNARC effect of the number seen also occurred in the response selection stage;(3)The brain processes the numbers seen and imagined differently at different stages.The bilateral hemispheres are activated with different degrees in different EEG components.And before generated in the brain,the processing speed of number imagined is more slowly than the number seen,but becomes faster subsequently. |
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