Biomedical subjects

Robert G Knight

Publications and source records attributed to Robert G Knight.

8 recordsLinked to original sources

PubMed2007

Speed of word retrieval in postconcussion syndrome.

Speed of information processing in persons with postconcussion syndrome (PCS) was examined using word fluency tasks. Twenty patients with PCS and twenty controls matched for age, gender, and occupation were given two word fluency tasks, and the speed of word generation was measured. Response latencies were analyzed to determine whether slowed retrieval or degradation of words in semantic memory was responsible for problems with word retrieval after traumatic brain injury. The PCS group recalled fewer words, had significantly longer interresponse times, and took significantly longer to generate their first word than the controls. There was no evidence that either structure loss or slowness in word retrieval from semantic memory could account for the word fluency deficits. Rather, the findings suggest that the primary cause of word retrieval difficulties in patients with PCS is a generalized slowness of cognitive processing.

Adult↗

PubMed2006

A controlled trial of homocysteine lowering and cognitive performance.

BACKGROUND: The results of observational studies suggest that plasma homocysteine concentrations are inversely related to cognitive function in older people. Our objective was to test the hypothesis that lowering the plasma homocysteine concentration improves cognitive function in healthy older people. METHODS: We conducted a two-year, double-blind, placebo-controlled, randomized clinical trial involving 276 healthy participants, 65 years of age or older, with plasma homocysteine concentrations of at least 13 micromol per liter. Homocysteine-lowering treatment was a daily supplement containing folate (1000 microg) and vitamins B12 (500 microg) and B6 (10 mg). Tests of cognition were conducted at baseline and after one and two years of treatment. Treatment effects were adjusted for baseline values, sex, and education. RESULTS: On average, during the course of the study, the plasma homocysteine concentration was 4.36 micromol per liter (95 percent confidence interval, 3.81 to 4.91 micromol per liter) lower in the vitamin group than in the placebo group (P<0.001). Overall, there were no significant differences between the vitamin and placebo groups in the scores on tests of cognition. CONCLUSIONS: The results of this trial do not support the hypothesis that homocysteine lowering with B vitamins improves cognitive performance. (Australian Clinical Trials registry number, ACTR NO 12605000030673.).

Aged↗

PubMed2006

The effects of distraction on prospective remembering following traumatic brain injury assessed in a simulated naturalistic environment.

The aim of this investigation was to assess deficits in prospective remembering following chronic traumatic brain injuries (TBI), under conditions of high and low distraction. We constructed a virtual shopping precinct from photographs, sounds, and video segments linked together. The street was divided into halves, a low distraction zone and a high distraction zone (with increased visual and auditory noise). Twenty persons with TBI (7 severe, 7 very severe, 6 extremely severe) and 20 matched controls completed ongoing and prospective memory tasks while "walking" along the street. In the ongoing task, participants were given ten errands to complete with a checklist accessible at any time. The prospective component required responding to three targets that appeared repeatedly. As predicted, the TBI group performed both the ongoing and the prospective components of the street task poorly compared with the controls and was more affected by distractions. The results suggest that the real-life deficits in memory skills reported by persons with TBI may become more apparent when remembering engages executive processes and that computer simulations can be used to construct sensitive measures of practical memory abilities.

Acoustic Stimulation↗

PubMed2006

Regression equations for predicting scores of persons over 65 on the rey auditory verbal learning test, the mini-mental state examination, the trail making test and semantic fluency measures.

OBJECTIVES: Scores on neuropsychological tests are often used to detect abnormal changes in cognition in older persons. Accordingly, it is important to have normative data that allow the abnormality of a test score to be determined precisely and accurately. Regression equations that estimate an expected score based on demographic or premorbid factors can be an efficient method of making normative comparisons. Our aim was to compute regression equations with age, gender and estimated premorbid IQ as predictors of scores on the Rey Auditory Verbal Learning Test (AVLT), the Trail Making Test (TMT), Mini-mental State Examination (MMSE) and measures of semantic fluency. DESIGN: All measures were administered to a group of 272 healthy older persons aged between 65 and 90 during the pre-treatment phase of a study evaluating the effect of nutritional supplements on cognition. Premorbid IQ was estimated using the National Ault Reading Test (NART). Stepwise multiple regression procedures were used to determine the weights to be applied to the predictor variables. RESULTS: Age and premorbid IQ were found to be significantly correlated with all test variables; gender correlated significantly with most scores. Regression equations based on the 3 predictor variables explained between 10% and 30% of the variance of the range of test scores. The use of these equations in clinical practice was illustrated. CONCLUSION: The significant correlations between the predictor variables and test scores justified computing a set of equations for use in interpreting data from older persons. The abnormality of the difference between predicted and obtained scores provides a convenient index of an individual's current level of neuropsychological functioning.

Aged↗

PubMed2005

The effects of traumatic brain injury on the predicted and actual performance of a test of prospective remembering.

PRIMARY OBJECTIVE: The aim of the present study was to assess prospective memory (PM) with a video-based task using naturalistic stimuli, in a group with long-term disabilities resulting from traumatic brain injury (TBI). The specific focus of the research was on comparing the accuracy of the TBI and control groups' estimates of successful completion of the prospective memory tasks. RESEARCH DESIGN: A group of 25 persons with TBI and 20 matched controls were compared on the video-based test of prospective remembering, on a test of retrospective memory (the Logical Memory sub-test of the Wechsler Memory Scale) and tests of executive dysfunction. Correlations between the neuropsychological and PM test scores were calculated and an item analysis of the PM test was undertaken. PROCEDURES: For the PM test, participants were given a scenario involving a robbery, and a list of tasks to be completed in a nearby city centre. The instructions were given twice and on the second occasion they were asked to rate the likelihood of remembering each item. They then watched a videotaped segment showing the perspective of a person first driving and then walking through an unfamiliar city. Their task was to recall each instruction when a relevant cue appeared. OUTCOMES AND RESULTS: The TBI group ratings of likelihood of recalling items were entirely equivalent to those made by the controls. On the PM test, however, their performance was significantly reduced. The performance of the TBI group on the PM test was correlated with scores on the Logical Memory and verbal fluency measures. CONCLUSIONS: The results showed that, although the TBI group performed more poorly on the PM task, their expectations about how much they would remember were comparable to those of the controls. The findings suggest that persons with TBI may have unrealistic expectations about how much they will remember in a novel situation. Awareness and acceptance of cognitive changes after TBI can be a significant issue for rehabilitation.

Adult↗

PubMed2004

Emotional specificity of startle potentiation during the early stages of picture viewing.

Potentiation of the startle blink reflex shortly after picture onset has only been reported in a sample of high animal-fear participants during fear-evoking stimuli. The experiment tested the emotional specificity of startle reflex modification at early (300 ms) and late (2-5 s) stages of picture viewing in an unselected sample (n=55). Participants viewed two negative picture categories, threat and disgust contents, in addition to neutral and positive pictures. Blink potentiation occurred for threat contents at both probe times, relative to neutral responses. Disgust contents only potentiated blinks relative to positive content responses. These results are inconsistent with a basic, prepulse interpretation of early startle modification and suggest that affective modification can be observed shortly after picture onset, depending on the specific emotional content of the picture.

Adolescent↗

PubMed2003

Assessing distress in caregivers of people with a traumatic brain injury (TBI): a psychometric study of the Head Injury Behaviour Scale.

This study examined the psychometric properties of the Head Injury Behaviour Scale (HIBS) using responses from 242 caregivers. The HIBS is a 20-item, scale describing common behavioural problems following traumatic brain injury (TBI), which are typical of dysexecutive syndrome. A principal components analysis was conducted on caregiver distress ratings for the 20 items comprising the HIBS and produced a two-factor solution with 10 items loading on each factor. Consequently, two sub-scales were derived and labelled Emotional Regulation and Behavioural Regulation. The sub-scales were found to have good internal-consistency reliability. It is suggested that the Emotional Regulation sub-scale assesses behaviours reflecting impaired emotional control, occurring during interactions with caregivers. The Behavioural Regulation sub-scale assesses problems typical of dysexecutive syndrome, but which carry less emotional valence for caregivers. The clinical implications of these findings are discussed and normative data provided for the two sub-scales.

Adaptation, Psychological↗

PubMed2002

Memory processing in Alzheimer's disease.

The aim of the present research was to examine automatic and controlled influences on memory processing in patients with Alzheimer's disease using the process-dissociation procedure. In Experiment 1, a source recognition procedure was used, and the patients were found to have significantly reduced estimates of automatic processing and capacity to recognise words seen during the study phase of the procedure. In Experiment 2, a detection of repetition procedure was used to determine whether automatic influences on memory decline as a dementia progressed. The patients showed the expected inability to detect repetition in their responding, but there was no evidence that estimates of automatic processing were predicted by mental status scores or by ratings of the severity of dementia. In the third study, a novel method for estimating parameters in the process-dissociation model, developed from the task used in Experiment 2, was tested in a student sample. In this procedure, participants first produce semantic associates with either high or low relatedness to a list of cue words. These responses are subsequently used in a paired associate learning paradigm to determine independent estimates of recollection and automatic processing. Evidence for the validity of this procedure was found in Experiment 3 and the procedure used to examine memory processing in a sample of persons with dementia (Experiment 4). The patient group was found to have a substantial deficit in controlled recollection and a reduced capacity for automatic memory processing.

Adult↗