Unlike prospective time perception paradigms, in which participants are aware that they have to estimate forthcoming time, little is known about retrospective time perception in normal aging and Alzheimer’s disease (AD). Our paper addresses this shortcoming by comparing prospective and retrospective time estimation in younger adults, older adults, and AD patients. In four prospective tasks (lasting 30 s, 60 s, 90 s, or 120 s) participants were asked to read a series of numbers and to provide a verbal estimation of the reading time. In four other retrospective tasks, they were not informed about time judgment until they were asked to provide a verbal estimation of four elapsed time intervals (lasting 30 s, 60 s, 90 s, or 120 s). AD participants gave shorter verbal time estimations than older adults and younger participants did, suggesting that time is perceived to pass quickly in these patients. For all participants, the duration of the retrospective tasks was underestimated as compared to the prospective tasks and both estimations were shorter than the real time interval. Prospective time estimation was further correlated with mental time travel, as measured with the Remember/Know paradigm. Mental time travel was even higher correlated with retrospective time estimation. Our findings shed light on the relationship between time perception and the ability to mentally project oneself into time, two skills contributing to human memory functioning. Finally, time perception deficits, as observed in AD patients, can be interpreted in terms of dramatic changes occurring in frontal lobes and hippocampus.
Patients with Alzheimer’s disease (AD) exhibit great deviations from true clock time, as they tend to show significant alterations in the judgment of time intervals (Nichelli, Venneri, Molinari, Tavani, & Grafman, 1993). Several investigations have provided support for this idea (Carrasco, Guillem, & Redolat, 2000; Caselli et al., 2009, Nichelli et al., 1993, Papagno et al., 2004 and Rueda et al., 2009). However, all these studies have been concerned by one facet of time perception, namely, prospective time perception.
In prospective time perception measures, participants are instructed in advance that they have to estimate time intervals. In retrospective measures, on the contrary, they are not. Prospective and retrospective timing are thought to be related to different processes: the first to timing mechanisms, the second to general cognitive mechanisms not specifically related to time, such as memory (Block, 2003). The common feature between retrospective timing and memory may lie in mental time travel. Mental time travel, or the ability to mentally project oneself backward in time to relive past experiences, is the mean feature of autonoetic consciousness characterizing episodic recall (Tulving, 2002 and Wheeler et al., 1997). Autonoetic consciousness, or mental time travel, is described as a sense of a subjective experience of time, and according to Tulving’s (2002) quote “no sense of subjective time, no mental time travel” (p. 2). According to this assumption mental time travel, allowing episodic recall, is likely to be heavily relying on retrospective time perception, or the subjective experience of the past.
