Biomedical subjects

Jos J Adam

Publications and source records attributed to Jos J Adam.

17 recordsLinked to original sources

PubMed2006

Effects of acute tryptophan depletion on cognition, memory and motor performance in Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is a neuropsychiatric disease, which is not only characterized by motor symptoms, but also by cognitive and psychiatric symptoms. It is hypothesized that some of the non-motor symptoms are related to the serotonergic deficiency that is present in PD. AIM: To study the influence of serotonin on cognition, memory and motor performance in PD. METHODS: In a double blind, randomized, placebo-controlled, cross-over design, the effect of acute tryptophan depletion (ATD) on the Visual Verbal Learning Task (VVLT), the Concept Shifting Task (CST), Simple Reaction Time Task (SRT), Finger Precuing Task (FPT) and the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS, Section 3) was investigated in 15 PD patients in early stages of their disease and 15 healthy volunteers, matched for age, sex and educational status. RESULTS: With the exception of the absence of a differential effect for PD patients with the long interval of the SRT, ATD produced similar effects in PD patients and control subjects on all tasks. These included impairment of delayed recall and delayed recognition on the VVLT, and improved SRT and FPT for 'short intervals'. The UPDRS in patients remained unaffected after ATD. CONCLUSION: Serotonin does not appear to play a disease-specific role in cognition and reaction time in early stage PD patients, nor does acute reduction of cerebral serotonin levels affect motor symptoms in a clinically relevant way.

Aged↗

PubMed2006

Distinct mechanisms for planning keypress and reaching responses: a developmental study.

This study examined developmental effects in the ability to use precue information for the planning of keypress and reaching responses. Participants from four age groups (7, 9, 13, and 21 year olds) performed a spatial precuing task either by pressing one of four response keys (keypress task) or by reaching directly toward one of the four target locations on the screen (reaching task). Reaction time data revealed striking age differences in the ability to use advance information in the keypress task, not in the reaching task. This dissociation confirms the hypothesis that distinct and separate mechanisms govern the planning of indirect keypress and direct reaching responses.

Adolescent↗

PubMed2006

Moving farther but faster: an exception to Fitts's law.

Fitts's law holds that movement time (MT) increases with longer distances. Here we report a violation of this law: When the target appears in a structured, linear display with placeholders indicating the possible target locations, MT to the most distant target is not longer than MT to the second most distant target, but rather tends to be shorter. Furthermore, the presence of placeholders attenuates the range effect that occurs in the absence of placeholders. These findings suggest that Fitts's law may be limited to egocentric visuomotor action, and that the visual control of hand movements may use allocentric, in addition to egocentric, spatial information.

Adult↗

PubMed2006

Saccadic latency as a function of target duration in a spatial localization task.

This study examined a potential confound in the inverse relationship between target duration and saccadic latency reported by Adam, Ketelaars, Kingma, and Hoek in 1993. Eight participants located a briefly flashed target by moving the eyes and the cursor toward its position in a (backward) mask condition and in a no-mask condition. Analysis showed similar saccadic latencies in both conditions, thereby refuting the potentially confounding role of the backward masking procedure. It is tenatively suggested that the longer saccadic latencies noted for shorter target durations may be associated with delayed accumulation of evidence for the detection of the target.

Adult↗

PubMed2005

Redundancy gain with static versus moving hands: a test of the hemispheric coactivation model.

A simple reaction time (RT) experiment was conducted to test the hypothesis that redundancy gain arises partly because of hemispheric coactivation. Stimuli were presented to the left or right of fixation, or redundantly to both, and the participants had to make keypress responses as rapidly as possible to stimulus onset. A "static" condition, in which the participants held their hands at rest, was compared with a "dynamic" condition, in which they moved their hands back and forth in an oscillating motion prior to stimulus onset. As predicted from the hypothesis of hemispheric coactivation, redundancy gain, measured as the decrease in mean RT to redundant stimuli as compared with single stimuli, was smaller in the dynamic condition than in the static one.

Adult↗

PubMed2004

Dissociating visual attention and effector selection in spatial precuing tasks.

In this study the authors tested and rejected a recent proposal that response precuing effects depend on the spatial extent of the precues rather than on the number of response choices. Moreover, the authors tested and supported the hypothesis that the number of effectors in the response set is an important determinant of spatial precuing effects. Results of 4 experiments consistently showed that keypress responses generated a qualitatively different pattern of precuing effects than did pointing and detection responses. Together, the results establish a strong dissociation between planning pointing responses and planning keypress responses and suggest that precuing effects in 1-effector and multiple-effector visuomotor tasks are dominated by distinct and separate mechanisms, visual attention and effector selection, respectively.

Adolescent↗

PubMed2004

Selective reaching: distracter effects on movement kinematics as a function of target-distracter separation.

The authors investigated distracter effects on the kinematics of reaching movements to determine when during reaching responses (reaction time, time to peak velocity, time after peak velocity, or peak velocity) distracter interference occurred and how target-distracter separation affected the locus of interference. Participants moved a pen on a digitizing tablet toward a target appearing with or without a distracter. With a small target-distracter separation, distracter interference occurred during time after peak velocity (similar amounts of interference from near and far distracters). With a large target-distracter separation, distracter interference occurred during time to peak velocity (more interference from near compared to far distracters). The results demonstrated that target-distracter separation is an important determinant of the locus of distracter interference.

Adolescent↗

PubMed2003

Selective attention deficits during human pregnancy.

Using a longitudinal design we provide evidence that selective attention - a key component of cognition concerned with selection and preparation - is compromised during pregnancy. Selective attention was operationalized by means of the finger precuing technique, which selectively prepares two of four finger responses. The precuing benefit was taken as a measure of selective attention. Pregnant women showed a significant smaller precuing benefit at week 36 of pregnancy than did the control women, indicating loss of selective attention. Thirty-two weeks after childbirth this performance decrement had vanished, reflecting a functional recovery.

Adult↗

PubMed2003

Preparing for perception and action (I): the role of grouping in the response-cuing paradigm.

Human skilled behavior requires preparatory processes that selectively make sensory and motor systems more efficient for perceiving the upcoming stimulus and performing the correct action. We review the literature concerning these preparatory processes as studied by response-cuing paradigm, and propose a model that accounts for the major findings. According to the Grouping Model, advance or precue information directs a dynamic process of subgroup making-that is, a process of stimulus- and response-set reconfiguration-whereby the internal representation of the task is simplified. The Grouping Model assigns a critical role to the unit of selection, with Gestalt factors and interresponse dependencies mediating the formation and strength of stimulus and response subgroups. In a series of five experiments, we manipulated perceptual and motoric grouping factors, and studied their independent and interactive effects on the pattern of precuing benefits. Generally, the results were consistent with the Grouping Model's account of response-cuing effects.

Adult↗

PubMed2003

The control of sequential aiming movements: the influence of practice and manual asymmetries on the one-target advantage.

The present experiment was conducted to explore the effect of practice on the one-target advantage in manual aiming, as well as asymmetries in intermanual transfer of training. Reaction and movement times for the first movement were longer in the 2-target than in the 1-target task, regardless of the amount of practice, hand preference and practice hand. When two movements were required, peak velocity was lower and, proportionally, more time was spent after peak velocity. Our kinematic results suggest that the one-target advantage is related to both predefined strategies as well as movement implementation processes during execution. Therefore, an integration of advance planning and on-line explanations for the one-target advantage is suggested. Regarding manual asymmetries, right-handers showed more transfer of training from the left to the right hand than vice versa. Left-handers exhibited a reversed pattern of asymmetric transfer of training to right-handers, but they were more disadvantaged using their non-dominant hand. These latter two findings have implications for models of manual asymmetry and upper limb control.

Adult↗

PubMed2003

Rapid visuomotor preparation in the human brain: a functional MRI study.

An important feature of human motor behaviour is anticipation and preparation. We report a functional magnetic resonance imaging study of the neuronal activation patterns in the human brain that are associated with the rapid visuomotor preparation of discrete finger responses. Our imaging results reveal a large-scale distributed network of neural areas involved in fast visuomotor preparation, including specific areas in the frontal cortex (middle frontal gyrus, premotor and supplementary motor cortex), the parietal cortex (intra-parietal sulcus, inferior and superior parietal lobe) and the basal ganglia. Our reaction time results demonstrate that it is easier to prepare two fingers on one hand than on two hands. This hand-advantage phenomenon was associated with relatively enhanced levels of activity in the basal ganglia and relatively reduced levels of activity in the parietal cortex. These findings provide direct evidence for differential activity in a distributed brain system associated with specific neuro-computational operations subserving fast visuomotor preparation.

Adult↗

PubMed2003

Distractor interference in selective reaching: dissociating distance and grouping effects.

In the present experiment, the authors sought to differentiate between a distance and a grouping explanation for the symmetric versus asymmetric patterns of distractor interference in selective reaching. Participants (N = 16) pointed to a green target that appeared either with or without a red distractor. Target-distractor separation was manipulated within an array of 5 closely grouped stimulus boxes, and distractor interference (difference in performance between trials with and trials without a distractor) was measured in reaction time, movement time, percentage errors, and movement endpoints. Small distances (5 mm) between target and distractor yielded a symmetric pattern of interference, whereas large distances (20 mm) yielded an asymmetric pattern, with more interference from near than from far distractors. Those findings support the distance account of distractor interference and refute the grouping account.

Adult↗

PubMed2003

Diminished performance on response-selection tasks in Type 2 diabetes.

Comparisons of visual perception, response-selection, and response-execution performance were made between Type 2 diabetes mellitus patients and a matched nondiabetic control group. 10 well-controlled male patients with Type 2 diabetes without diabetic complications (M age 58 yr.) and an age and IQ-matched non-diabetic control group consisting of 13 male healthy volunteers (M age 57 yr.) were included. Significant differences were found only between the two groups on response-selection performance, which concerns the selection and preparation of an appropriate motor action.

Aged↗

PubMed2002

The one-target advantage: advanced preparation or online processing?

The one-target advantage refers to a shorter movement time for one- target aiming movements, in comparison to aiming attempts followed by a second movement. Theoretical explanations of the one-target advantage vary in the extent to which they attribute this phenomenon to prior planning or to online control mechanisms. In this research, we attempted to gain insight into the control of sequential aiming movements by manipulating the availability of online feedback during this first or second movement component. When the participants vision was occluded during the first movement (Experiment 1) or during the second movement (Experiment 2), their performance was affected, showing that vision was important for online control of the movement sequence. A one-target advantage was found when the second movement was in the same direction as the first, but not when it was reversed with respect to the home button. Both prior planning and online control processes contribute to the one-target advantage. The degree to which these processes are important for limb control depends on the specific task demands

Adult↗

PubMed2002

Effects of distractor load and temporal target-distractor separation on numerical comparison performance: a stimulus-competition approach.

Effects of distractor load and temporal separation between target and distractor onset were studied in a selective attention task. Two experiments required 128 participants to decide as quickly and accurately as possible which of two spatially separated one-digit numerals was larger. Targets were either preceded or succeeded by distractors with intervals of 0, 33, 83, 133, 183, and 233 msec. In Exp. 1, the target digits could appear with 0, 1, 2, or 3 one-digit distractors numerals, representing four levels of distractor load. In Exp. 2, three asterisks were used as distractors. Interference effects of digit distractors varied with distractor load and temporal separation between target and distractor onsets. Moreover, the effects of distractors preceding the target differed from distractors succeeding the target. The pattern of results provided evidence that distractor-interference effects originated from stimulus competition for selection in visual short-term memory. The results were interpreted in terms of attentional engagement theory of Duncan and Humphreys.

Adolescent↗

PubMed2002

Selective reaching: evidence for multiple frames of reference.

Students participated in 3 experiments investigating the use of environment- and action-centered reference frames in selective reaching. They pointed to a green target appearing either with or without a red distractor. Target-distractor distance was manipulated, and distractor interference (difference between distractor trials and no-distractor trials) was measured in reaction time, movement time, and movement endpoint. Target-distractor distance determined the dominant frame of reference. Small distances evoked an environment-centered framework that encoded targets within an external context. Large distances evoked an action-centered framework that encoded targets relative to the start position of the hand. Results support the hypothesis that the brain represents spatial information in multiple frames of reference, with the dominant frame of reference being dependent on the task demands.

Adolescent↗

PubMedDate not supplied

Challenging the serotonergic system in Parkinson disease patients: effects on cognition, mood, and motor performance.

BACKGROUND: Parkinson disease (PD) is a neuropsychiatric disease that is characterized by motor and neuropsychiatric symptoms. Multiple neurotransmitter systems, including the serotonergic system, are involved in the pathophysiology of this disease. The exact role of the serotonergic system in PD is still unclear. OBJECTIVE: To investigate the role of serotonin on specific aspects of cognition, mood, and motor performance in PD. METHODS: In a double-blind, randomized, placebo-controlled, crossover design, the effects of a nonspecific serotonergic challenge with citalopram, a selective serotonin reuptake inhibitor, and a 5-HT1a receptor-specific challenge with buspirone on the Visual Verbal Learning Task, Concept Shifting Task, Profile of Mood State Questionnaire, motor section of the Unified Parkinson Disease Rating Scale (section 3), Simple Reaction Time Task, and Finger Precuing Task were studied in 21 PD patients in early stages of their disease and 21 age-, sex-, and education-matched healthy volunteers. RESULTS: The serotonergic challenges resulted in similar effects for both groups. No changes of scores on the cognitive tasks (Visual Verbal Learning Task and Concept Shifting Task) were observed. Results of the Profile of Moods State Questionnaire indicated that, at baseline, PD patients scored less than controls on all 5 subscales. Motor performance (measured by reaction time) was negatively affected by the interventions. CONCLUSIONS: The effects of nonspecific and 5-HT1a receptor-specific challenging of the serotonergic neurotransmitter system had similar effects in both PD patients and healthy control subjects. These findings indicate that serotonergic function is not impaired in early PD and that serotonin, although involved in the pathophysiology of PD, does not seem to play a direct role in cognition, mood, and motor performance in PD patients, but may be involved in hypokinesia.

Affect↗