An alteration of serial dependence in an aging population with mild cognitive impairment

In an ever changing world, retention of past information is necessary to stabilize our visual perception. This adaptive process is called serial dependence. While an effect was evidently found in several studies in adults, little is known about an effect of serial dependence in a healthy aging population or an aging population with mild cognitive impairment (MCI). Two possible theories can be seen in MCI patients. First, retention of previous memory could be difficult in MCI patients due to memory impairment. On the other hand, an effect of serial dependence might be stronger. As memory impairment could cause the patients to rely more on previous information. To test our hypotheses, our group recruited 17 healthy aging adults and 19 MCI patients aged from 55 to 82 years old. Visual search task was used to evaluate the subject's attention and working memory. All 12 stimuli were spatially arranged in a circular fashion. The cue appears on the screen to make participants attend to the specific location. Then, participants have to answer whether the shape at the target location is a diamond shape or hourglass. Accuracy and reaction time were recorded. We found that when the current stimulus appears in the same position as the previous trial. MCI patients responded faster and more accurately than when the stimuli appeared in other positions. (p-value = 0.0002 and 0.006 respectively) While in a healthy aging group, there was no difference between accuracy and reaction time across positions. A group comparison demonstrated that there is a stronger effect of serial dependence in MCI patients compared to control groups in terms of reaction time (p-value = 0.028) but not accuracy. The knowledge found from this study can be used to understand mechanisms of pathophysiologic change in MCI patients. Further studies into this effect could be a crucial step to develop a specific intervention for MCI patients.