Speed of processing within semantic memory following severe closed head injury

Implicit memory influences on metamemory during verbal learning after traumatic brain injury

PURPOSE

Prior research has shown that individuals with traumatic brain injury (TBI) may be overconfident in their judgments of learning (JOLs; online measures of self-monitoring of learning and memory). JOLs had been presumed to be driven by explicit processes, but recent research has also revealed implicit memory involvement. Given that implicit learning mechanisms are often intact in those with TBI, the purpose of this study was to investigate whether priming and antipriming of immediate and delayed JOLs in individuals with TBI might affect their overconfidence.

METHOD

A standard 3-field masked priming paradigm was combined with a paired-associate learning task with JOLs and administered to individuals with TBI and matched controls (18 per group). In each trial, a subliminal masked stimulus was immediately followed by supraliminal presentation of a word pair for study; participants also made immediate and delayed JOLs, with cued-recall testing 10 min after study and judgment.

RESULTS

Antipriming significantly lowered JOLs and overconfidence for both groups, whereas delaying JOLs significantly improved recall for both groups.

CONCLUSIONS

The results suggest that JOLs may be influenced by subliminal implicit memory. Clinical implications include the possible use of antipriming to reduce overconfidence after brain injury and delaying JOLs to improve recall.

Recollecting, recognizing, and other acts of remembering: an overview of human memory

The question of whether memory is important to human existence is simple to answer: life without memory would be devoid of any meaning. The question of what memory is, however, is much more difficult to answer. The main purpose of this article is to provide an overview of memory function, by drawing distinctions between different memory systems, specifically declarative (ie, conscious) versus nondeclarative (ie, nonconscious) memory systems. To distinguish between these larger systems and their various components, we include discussion of deficits in memory that occur as a consequence of brain injury and normative aging processes. Included in these descriptions is discussion of the neuroanatomical correlates of each memory component described to illustrate the importance of particular brain regions to different aspects of memory function.

The Effect of Moderate to Severe Traumatic Brain Injury (TBI) on Different Aspects of Memory:A Selective Review

Deficient learning and memory are frequently reported as a consequence of traumatic brain injury (TBI). Because of the diffuse nature of the injury, patients with TBI are not the ideal group for studying brain-behavior relations. Nevertheless, characterization of the memory breakdown following TBI could contribute to the assessment and rehabilitation of this patient population. It is well documented that memory is not a unitary system. Accordingly, in this article I review studies that have investigated the long-term effect of moderate to severe TBI on different memory aspects, including explicit and implicit tests of memory. This review demonstrates that TBI affects a large range of memory aspects. One of the conclusions is that the memory impairment observed in TBI patients could be viewed, at least to some degree, as a consequence of a more general cognitive deficit. Thus, unlike patients suffering from global amnesia, memory in patients with TBI is not selectively impaired. Nevertheless, it is possible to detect a subgroup of patients that do meet the criteria of amnesia. However, the most common vulnerable memory processes following TBI very much resemble the memory deficits reported in patients following frontal lobe damage, e.g., difficulties in applying active or effortful strategy in the learning or retrieval process. The suggested similarity between patients with TBI and those suffering from frontal lobe injury should be viewed cautiously; considering the nature of TBI, patients suffering from such injuries are not a homogeneous group. In view of this limitation, the future challenge in this field will be to identify subgroups of patients, either a priori according to a range of factors such as severity of injury, or a posteriori based on their specific memory deficit characteristics. Such a research approach has the potential of explaining much of the variability in findings reported in the literature on the effect of TBI on memory.

Selective adult age differences in an age-invariant multifactor model of declarative memory

Confirmatory factor analysis was used to test competing models of declarative memory. Data from middle-aged participants provided support for a model comprised of 2 2nd-order (episodic and semantic memory) and 4 1st-order (recall, recognition, fluency, and knowledge) factors. Extending this model across young-old and old-old participants established support for age invariance. Tests of group differences showed an age deficit in episodic memory that was more pronounced for recall than for recognition. For semantic memory, there was an increase in knowledge from middle to young-old age and thereafter a decrease. Overall, the results support the view that episodic memory is more age sensitive than semantic memory, but they also indicate that aging has differential effects within these 2 forms of memory.

Older age, traumatic brain injury, and cognitive slowing: some convergent and divergent findings

Reaction time (RT) meta-analyses of cognitive slowing indicate that all stages of processing slow equivalently and task independently among both older adults (J. Cerella & S. Hale, 1994) and adults who have suffered a traumatic brain injury (TBI; F. R. Ferraro, 1996). However, meta-analyses using both RT and P300 latency have revealed stage-specific and task-dependent changes among older individuals (T. R. Bashore, K. R. Ridderinkhof, & M. W. van der Molen, 1998). Presented in this article are a meta-analysis of the effect of TBI on processing speed, assessed using P300 latency and RT, and a qualitative review of the literature. They suggest that TBI induces differential slowing. Similarities in the effects of older age and TBI on processing speed are discussed and suggestions for future research on TBI-induced cognitive slowing are offered.

Speed of information processing in traumatic brain injury: modality-specific factors

OBJECTIVE

To assess speed of information processing by two serial addition tests (one visual, one auditory) in individuals with moderate-to-severe traumatic brain injuries (TBIs) and in a healthy, normal control group (NC). The tasks were designed to equate and control for accuracy of performance across the TBI and NC groups, thus allowing for quantification of information processing speed.

DESIGN

Performance across groups and tasks were compared using 2 x 2 repeated measure analyses of variance (ANOVAs). In addition, each individual's processing speed was used to adjust rate of stimulus presentation on a subsequent "rehabilitation" trial to determine further whether this adjustment equated accuracy of performance.

SETTING

Rehabilitation hospital.

PATIENTS

22 outpatients with moderate-to-severe TBI (6 women, 16 men; mean age = 34.6 years; duration of loss of consciousness = 22.6 days) and 20 age- and education-matched healthy controls.

RESULTS

Processing speed was slower in TBI subjects, relative to controls and was significantly related to measures of executive functioning for those with TBI. Relative to controls, speed of processing in the TBI group was disproportionately slower when information was presented in the auditory, relative to the visual, modality.

CONCLUSIONS

Speed of information processing is a major impairment in those with TBI when unconfounded by performance accuracy. The modality-specific impairment observed in the TBI group may, in part, be due to a greater within-modality interference effect created by the auditory version of the task. By manipulating information at a pace customized for an individual through compensatory strategies and environmental modifications, information-processing performance of TBI participants can be enhanced significantly.

Deficient intentional access to semantic knowledge in patients with severe closed-head injury

Patients after severe closed-head injury (CHI) demonstrate reduced ability to spontaneously utilize semantic memory during word-list memory tests and when requested to answer questions regarding general knowledge. However, they show normal lexical facilitation in both automatic and intentional semantic priming paradigms. The present study was aimed at investigating two alternative hypotheses a) that the deficit in semantic processing after CHI is the result of impaired access to an otherwise normal semantic system or b) that it reflects a loss of knowledge from a deteriorated semantic store. For this purpose, the performance of 15 CHI patients on an automatic Semantic Priming paradigm and on tests of Picture Naming and Semantic Judgment were compared to those of 14 normal controls (NC). Although CHI patients' reaction times were significantly slower than those of NCs, the semantic priming effect was comparable in the two groups. Instead, CHI patients performed significantly worse than NCs in the naming and semantic judgment tasks. These results provide evidence that CHI patients access semantic memory automatically at a normal rate. However, when the task is more demanding in terms of processing requests, then CHI patients' performance becomes defective.

Slow information processing after very severe closed head injury: impaired access to declarative knowledge and intact application and acquisition of procedural knowledge

As an explanation of the pattern of slow information processing after closed head injury (CHI), hypotheses of impaired access to declarative memory and intact application and acquisition of procedural memory after CHI are presented. These two hypotheses were tested by means of four cognitive reaction-time tasks, a semantic memory task, a memory comparison task, a mental rotation task and a mirror reading task. These tasks were administered on two different days to 12 survivors of a CHI tested more than 5 years after injury and a healthy control group of comparable age and education. In three tasks the difficulty of access to declarative knowledge was varied and it was expected that this would slow the CHI group more than the controls. In two tasks opportunities for procedural learning were provided by repeatedly presenting the same cognitive tasks and in one task, the difficulty of access to procedural memory was varied. It was expected that the CHI group would profit as much from this as would the control group. Both hypotheses were supported.

Performance of children with traumatic brain injury on the Cognitive Assessment System

Children and adolescents with traumatic brain injury (TBI) were compared to a matched sample of neurologically normal children and adolescents on several measures of cognitive processing. Each of the children in the TBI group had experienced a closed head injury of moderate to severe magnitude. Participants in both the TBI (n = 22) and control (n = 22) groups ranged in age from 9 to 17 years and lived in the midwestern United States. They were all administered the Cognitive Assessment System (Naglieri & Das, 1997a). Children with TBI earned significantly lower scores in the domains of Planning and Attention than the matched control group. Within-group comparisons showed that the TBI group s Planning and Attention scores were significantly lower than their Simultaneous and Successive scores. The results are consistent with previous literature demonstrating poor performance on measures of attention and executive functions among children who have experienced TBI.

Semantic memory following pediatric head injury: relationship to age, severity of injury, and MRI

The effects of closed head injury (CHI) severity (mild vs. severe) and age at injury were analyzed in a longitudinal study (3. 12 months postinjury) of semantic memory which used magnetic resonance imaging (MRI) to characterize focal brain lesions. Semantic memory was evaluated by word and category fluency, semantic verification, semantic clustering in word list recall, and vocabulary. Episodic memory was assessed by word list recall. Comparison of normal control (n = 104) data with the patients' data (n = 77) at 3 months postinjury disclosed semantic and episodic memory deficits in the severe CHI patients. Analysis of the longitudinal data revealed significant effects of age at injury for all of the semantic memory measures. The effects of injury severity were confined to the latency of verifying correct statements. Volume of left frontal and extrafrontal lesions was predictive of performance on several semantic memory measures, but less robust for right hemisphere lesions.

Verbal rehearsal and memory in children with closed head injury: a quantitative and qualitative analysis

Nine closed head injured (CRI) children (mean age = 11.4 years) with post-onset intervals of seven months to eight years were studied. The CRI children ranged from mild-moderate to severely impaired. Nine normally developing children (mean age = 10.9 years) served as controls. An overt rehearsal free recall task was used. Subjects were instructed to "think aloud" following presentation of each item to-be-recalled. Quantitative analyses suggested impaired verbal recall and inefficient, passive rehearsal strategy use in severely injured subjects. Mild-moderate subjects performed similarly to controls and exhibited active rehearsal strategy use. Qualitative analysis revealed differences between CRI subjects and controls' range of rehearsal strategies, monitoring and metamemory. Implications for clinical assessment and intervention with respect to use of rehearsal strategies are discussed.