This study investigated time-based prospective memory (PM) performance in 76 younger and 76 older adults with a time-monitoring task in which participants were required to press a designated key every 5 minutes while watching a movie. Participants were assigned to two conditions, free and fixed monitoring. In free monitoring participants could check a clock when they wanted, but in fixed monitoring they were restricted a maximum of six times every 5 minutes. We also investigated the involvement of time perception, inhibition, and updating in time-based PM performance. We hypothesised that participants with inefficiencies in those three cognitive functions would have less strategic monitoring behaviour and would also be less accurate at the target time. In the free-monitoring condition older adults checked the clock more frequently than younger participants, but presented with a similar pattern of monitoring behaviour and increased their frequency of clock checking closer to the target time. In the fixed-monitoring condition younger participants checked the clock more frequently than older adults and showed a strategic pattern of monitoring. Older adults did not show strategic use of clock checking and their monitoring function remained unchanged. Differences in PM accuracy and monitoring behaviour are discussed according to different involvement of cognitive abilities.

Prospective memory (PM) is the ability to remember to perform a future action at a specified later time, which is investigated through the use of event-based and time-based tasks. Prior investigations have found that PM is impaired following traumatic brain injury (TBI). However, there is limited information regarding the cognitive functions that mediate TBI and PM performance. Thus, this study investigated time-based PM in TBI patients, and the relationship among time-based PM, time perception, and executive functions. To accomplish this objective, 18 severe TBI patients and 18 healthy matched controls performed a time-based PM task, a time reproduction task, and two executive functions (Stroop and n-back) tasks. While both groups increased their monitoring frequency close to the target time, TBI patients monitored more and were less accurate than healthy controls at the target time confirming the time-based PM dysfunction in these patients. Importantly, executive functions, particularly inhibition and updating abilities, were strongly related to time-based PM performance; both time perception and executive functions are involved in time-based prospective memory in controls, whereas, only executive functions appear to be involved in TBI time-based prospective memory performance. (JINS, 2012, 18, 1–9)

Adequate temporal abilities are required for most daily activities. Traumatic brain injury (TBI) patients often present with cognitive dysfunctions, but few studies have investigated temporal impairments associated with TBI. The aim of the present work is to review the existing literature on temporal abilities in TBI patients. Particular attention is given to the involvement of higher cognitive processes in temporal processing in order to determine if any temporal dysfunction observed in TBI patients is due to the disruption of an internal clock or to the dysfunction of general cognitive processes. The results showed that temporal dysfunctions in TBI patients are related to the deficits in cognitive functions involved in temporal processing rather than to a specific impairment of the internal clock. In fact, temporal dysfunctions are observed when the length of temporal intervals exceeds the working memory span or when the temporal tasks require high cognitive functions to be performed. The consistent higher temporal variability observed in TBI patients is a sign of impaired frontally mediated cognitive functions involved in time perception.