关键词: 轻度认知障碍, 时间知觉障碍, 回溯式时距估计任务, 长时距知觉

Abstract: Mild Cognitive Impairment (MCI) denotes the clinical stage between healthy aging and Alzheimer’s disease (AD). There is emerging evidence indicating that patients with AD suffer from time distortion, but it remains controversial whether MCI patients also show compromised ability in time perception. The current study aims to investigate the time perception ability of MCI patients and to examine whether time distortion can be observed at the pre-clinical stage of Alzheimer’s disease.
Using the retrospective time estimation task, the current study tested 34 MCI patients and 34 healthy controls, who are matched in age, education, and gender. Before the experiment, participants were tested with Mini-Mental State Examination (MMSE) by a clinician, and the diagnoses and group allocation remained unknown to the participants until the end of the experiment. After diagnoses, participants were exposed to the target interval by engaging in a naming task. In this task, participants were first given an eye-sight check and correction. And then, following the naming task instruction and practice, they were informed to verbally report the names of 36 objects and 36 scenes in the pictures on a computer screen. There was no time limit for their responses, and their responses were recorded at the same time. While accomplishing the naming task, all participants were surprisingly asked to estimate the clock time between the onset of eye-sight check and the end of naming task. The target intervals ranged between 15 to 40 minutes, and participants were unaware of the timing task when they were exposed to the target intervals.
In data analysis, interval ratio (estimated clock time/original clock time) and interval distortion ratio (|estimated clock time-original clock time|/original clock time) were calculated respectively to indicate the overestimation/underestimation tendency and the degree of estimation distortion. With independent samples t-tests, it was found that though MCI patients did not differ significantly from the control groups in the naming task, they underestimated target interval (M= .81, SD= .18) to a larger extent than healthy controls (M= .95, SD= .16). In addition, the distortion in time estimation was also larger for MCI patients (M= .23, SD= .12) than that for the control group (M= .13, SD= .10).
In general, the results suggest that MCI patients showed significant deficit in timing long intervals retrospectively. Such deficit could possibly be attributed to the memory decline of MCI patients, according to recall-based account of timing. MCI patients would underestimate the target duration with fewer details being retrieved about the target episode, as one’s remembered duration is largely determined by the amount of recalled information. In addition, the compromised ability in time perception of MCI patients could also be explained by the attention-based timing theory, that the estimated duration would be shorter when less attention is allocated to the time aspect of the target episode. In this view, as fewer attentional resources would be available and attributed to the temporal aspect during the naming task for MCI patients, the estimated duration would be prone to underestimation. Moreover, the dysfunction of internal clock may also account for the observed findings, that the declined pace of internal clock and the illusion of time acceleration would possibly be severer for MCI patients than for the healthy elderly, which leads to the significant group difference in retrospective timing.
The current findings provide direct evidence for the time distortion in MCI patients, which provides valuable insights into the progression of time distortion from normal aging to AD and may contribute to the early clinical diagnosis of Alzheimer’s disease. In addition, rather than grounding research in prospective timing and short intervals below 1 to 2 minutes, this study creatively investigates time perception for long intervals above 15 minutes using the retrospective task, which enables the full understanding of time perception at different time scales and in different paradigms. Moreover, further studies are needed to investigate the cognitive mechanisms and neural underpinnings of timing dysfunction elicited by MCI or AD.

Key words: MCI, time distortion, retrospective time estimation, long interval perception