Franca Stablum

Attention and Control Deficits Following Closed Head Injury

This study was aimed at identifying the impaired attentional components in patients who had sustained a severe CHI several years before. A group of 14 CHI patients and a Control group (matched for age, sex and education) were tested. Experiment 1 used a dual-task paradigm (Umiltà et al., 1992). The double task-single task difference was greater for the CHI group, indicating a specific damage at a central executive stage where decision are made and responses are coordinated. Experiment 2 used a task-shifting paradigm (Morra and Roncato, 1986). The cost of shifting from one task to the other was greater for the CHI group, but only in the Short Series Condition where a new task-program could be pre-activated. Experiment 3 studied visual selective attention using Navon paradigm (1977); in this case, there was no difference between patients and controls.

Executive Functioning Following Mild Closed Head Injury

This study was aimed to identify impaired attentional components in mild CHI patients. The CHI features taken into account were age (< or = 30 vs. > 30 years), loss of consciousness (yes vs. no), and time after injury (few days vs. some months). The groups tested were composed of 26 patients and 26 controls (matched for age, sex and education). Experiment 1 used a dual-task paradigm (Umiltà et al., 1992), which taps executive functions. The double task-single task difference was greater for the CHI group, but only for patients older than 30 years and/or with consciousness loss. Two years after injury, some of these patients were retested: The results showed that this deficit was still present. Experiment 2 studied visual selective attention using the Navon (1977) paradigm. In this case, there were no differences between patients and controls. The results are discussed with reference to the anterior/posterior attention systems.

Different methods for reproducing time, different results

One of the most widely used tasks for investigating psychological time, time reproduction, requires from participants the reproduction of the duration of a previously presented stimulus. Although prior studies have investigated the effects of different cognitive processes on time reproduction performance, no studies have looked into the effects of different reproduction methods on these performances. In the present study, participants were randomly assigned to one of three reproduction methods, which included (a) just pressing at the end of the interval, (b) pressing to start and stop the interval, and (c) maintaining continuous pressing during the interval. The study revealed that the three reproduction methods were not equivalent, with the method involving keypresses to start and stop the reproduction showing the highest accuracy, and the method of continuous press generating less variability.

An investigation of prospective memory functions in people with traumatic brain injury using Virtual Week

Prospective memory (PM) refers to memory for future intentions and is critically linked to independent living. Previous laboratory research has shown that people who have sustained a traumatic brain injury (TBI) have difficulties with PM, but few of these have used measures of PM that closely represent the types of PM activities that occur in everyday life. One measure that incorporates more ecologically valid tasks, and which also allows systematic investigation of different PM task parameters (regular, irregular, and event and time based), is Virtual Week. Consequently, in the present study, Virtual Week was administered to participants with TBI (n = 18) and demographically matched controls (n = 18). Consistent with considerable prior literature, the results indicated that people with TBI had significant difficulties executing PM tasks, with these deficits more pronounced for time-based than for event-based tasks. These data point to there being a relatively global PM deficit in people with TBI. Of particular interest was the finding that the magnitude of TBI impairment was consistent across regular and irregular tasks. Because the key distinction between these tasks is that they place low and high demands on retrospective memory, respectively, these data suggest that failures of retrospective memory are not the major cause of TBI-related impairment in PM. The implications of these results for the assessment and rehabilitation of PM impairment in people with TBI are discussed.

Time-based prospective memory in severe traumatic brain injury patients: the involvement of executive functions and time perception.

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.

ERP components activated by the “GO!” and “WITHHOLD!” conflict in the random Sustained Attention to Response Task

The present study investigates the event related potential (ERP) components associated with the random version of the Sustained Attention to Response Task (SART). The random SART is a Go/No-Go task in which the No-Go target appears unpredictably and rarely. In the present experiment, the EEG was recorded from 58 electrodes with mastoids as reference. As expected, the N2 and P3 were larger in the No-Go trials compared to the Go trials, with the P3 more frontal for the No-Go trials compared to the Go trials. The functional role of the N2 and P3 in the No-Go trials is discussed comparing our results to the fixed SART results obtained by Dockree et al. [Dockree P. M., Kelly S. P., Robertson I. H., Reilly R. B., & Foxe J. J. (2005). Neurophysiological markers of alert responding during goal-directed behaviour: A high-density electrical mapping study. NeuroImage, 27, 587-601]. In addition, the lateralized readiness potential (LRP) was computed. The absence of an LRP in the No-Go trials suggests that a central inhibitory mechanism intervenes to prevent the preparation and execution of a dominant motor response.

Rehabilitation of endogenous task shift processes in closed head injury patients

This paper reports a study that was aimed to rehabilitate executive functions in CHI patients. When a subject is engaged in two speeded tasks, not simultaneously but with some form of alternation, the response is slower to an item of task A if it was preceded by an item of task B, than when it was preceded by an item of task A. This shift cost is small when subjects can prepare in advance for the new task (endogenous task shift), whereas the cost is much greater when preparation is not possible (exogenous task shift). The groups tested comprised 20 severe closed head injury (CHI) patients (10 who underwent treatment and 10 controls), 8 mild CHI patients, and 18 non-brain damaged (NBD) controls. In the present study, the shift cost was greater for severe CHI patients than for NBD controls. Treatment consisted of five sessions, in which an endogenous task shift paradigm was used. A significant reduction of the endogenous shift cost from assessment to retest was found. The reduction remained stable at the 4-month follow-up session. These results are not simply due to retesting, as the control patients did not show any improvement at retest. Interestingly, no reduction of exogenous task shift cost was found. The results showed also that the beneficial effect of the treatment generalises to other executive functions. Portions of these data were presented at the Nineteenth European Workshop on Cognitive Neuropsychology, Bressanone (Italy), 21–26 January 2001, and at the Second International Vipiteno/Sterzing Conference on Neuropsychological Rehabilitation after Brain Injury, Vipiteno (Italy), 9–12 June 2004.

Monitoring behaviour in a time-based prospective memory task: The involvement of executive functions and time perception

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.

Time perception in severe traumatic brain injury patients: a study comparing different methodologies.

In this study, we investigated time perception in patients with traumatic brain injury (TBI). Fifteen TBI patients and 15 matched healthy controls participated in the study. Participants were tested with durations above and below 1s on three different temporal tasks that involved time reproduction, production, and discrimination tasks. Data variables analyzed included amount of errors, relative errors, and coefficient of variation. Both groups completed a neuropsychological battery that included measures of attention, working memory, and executive functions. Results revealed significant differences between groups on the time reproduction and discrimination tasks, whereas groups showed similar performance on the time production task. Correlation analyses showed involvement of attention, working memory and executive functions on the time reproduction and time discrimination tasks, but there was no involvement on the time production task. These findings suggest that TBI does not impact specific temporal function. Rather, impairments in attention, working memory and executive function abilities may explain lower temporal performance in people with TBI.

Selective effect of closed-head injury on central resource allocation : evidence from dual-task performance

Abstract. Two dual-task experiments are reported bearing on the issue of slower processing time for severe chronic closed-head injury (CHI) patients compared to matched controls. In the first experiment, a classical psychological refractory period (PRP) paradigm was employed, in which two sequential stimuli, a pure tone and a colored dot, were presented at variable stimulus onset asynchronies (SOAs), each associated with a distinct task. The task on the tone required a speeded vocal response based on pitch, and the task on the colored dot required a speeded manual response based on color. In the second experiment, either one or three masked letters was presented, followed by a pure tone at variable SOAs. The task on the letters required a delayed report of the letters at the end of each trial. The task on the tone required an immediate manual response based on pitch. In both experiments, both CHI patients and matched controls reported an SOA-locked slowing of the speeded response to the second stimulus, a PRP effect. The PRP effect was more substantial for CHI patients than for matched controls, suggesting that a component of the slower processing time for CHI patients was related to a selective increase in temporal demands for central processing of the stimuli.