| Since the day of human is human beings, we are surrendered by every kind of dangerous stimulus. In the long run of human evolution, human gets different kinds of ability to dispose danger. In the book of "evolutionary psychology" of Darwin's, function of each organism was supposed as products of environment adaption, if the function is not need anymore, it will wipe out as time goes by. As a product of long-term evolution, fear emotion is as important as it is described [1]. When facing threat stimuli, alert system is fast inspired and quick response is made, anymore, experience accumulated and conditional reflex are formed when the same situation come up again. Like everything has two sides, fear can bring good and bad. If not treat fear emotion appropriate, it will affect physiological and social functions. Night time as a special period of one day can't be eliminated. Danger frequently occurs under the cover of dark and gets more close to the prey. As for physical weak, humans are naturally become the target in the dark night. To adaptation the dark night, from the earliest people until now, from drilling wood to make fire to brilliantly illuminated, whatever means take, human improve visibility in dark night in order to distinguish fear stimuli from dark background. Therefore, to investigate the affect dark night played on fear stimuli processing has more realistic significance than daylight.This research trying to adopt the same neutral stimuli and fear stimuli, in the first time to investigate the affect dark night played on fear stimuli processing so as to give more intuitive and powerful evidence to prove night-time fear is fear threats lurking in dark night. Therefore, this is made up with a behavior research which is day/night fear strength estimation and high-resolution event related potential (ERP) technology research which is an implicit paradigm oddball task trying to find out whether test environment can affect neutral and fear stimuli processing also its neutral mechanism along with it.The first part adopts" fear intensity estimation task" to neutral and fear materials to study whether the feeling fear strength is different between daylight and dark night by applying of 9 point scale. The aim of this task is to find out whether night impacts fear feeling comparing with daylight from the angle of explicit. Experimental results show that:according to the score, there is no significant difference to neutral stimuli between daylight and dark night. However, night truly has affect on fear strength, fear strength of fear stimuli are significantly higher at night than in day time. Night can reduce fear threshold and makes the feeling of fear much stronger.EXP2:We apply ERP technology, using oddball paradigm and two category of material (neutral pictures and fear pictures) as deviation stimulation. The probability of standard stimuli a cup is 80%, as deviation stimuli fear stimuli and neutral stimuli take probability of 10% for each part. The task of subject is to distinguish the standard stimulation or deviation stimulation. Such design can imitate threat stimuli occur without expectation. The result of ERP show:at the time window of 80-120ms, 150-200ms,200-260ms,350-420ms, there is a stimuli type main effect. Anymore, at the time window of 450-550ms and 600-1000ms, there is a stimuli type by test environment interaction effect. Further analysis found that neutral stimuli didn't display day/darkness different on senior composition N4 and LPP. But fear stimuli processing did has night time effect as N4 and LPP are bigger than it is at daytime. N1,P2,N2,P3 those ingredients has main effect of stimuli type that shows stimuli type effect do not change with the change of test environment. Fear stimulating in any time can cause more cerebral resources processing, this comes from the need of survive evolution, only fast to identify and response threat stimuli can human being gets survived. Neutral stimulation are not danger to human so it won't get much more brain resource to process.Fear stimuli appear in dark night are more likely to raise people's fear feeling. Because dark cover threat so that it can get more close to it's pray and more easily succeed. This makes fear stimuli rouse more brain resource and intense fear feeling. This is the reason why in dark fear feeling will last longer when something threat stimuli comes up.Overall, fear to threats is the product of evolution; darkness is a time of fear period. Research from behavior experiments and ERP experiment to investigate the affect darkness puts on fear stimuli processing. From the result of behavior data and ERP data, darkness obviously has affect on fear stimuli processing. ERP data tell us fear strength to neutral stimuli won't change as circumstances change. But fear stimuli arouse different fear feeling between day and darkness even the same material. Darkness can intensify fear feeling. The reason is that fear stimuli threat to human. From ERP result, we know darkness can stir up more cerebral resources and internal senior ingredients, so the ERP wave at night are much more bigger than daylight. |
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