Examining neurochemical determinants of inspection time

Visual processing speed in freezing and non-freezing Parkinson's disease patients

Introduction

Parkinson's disease patients are usually characterized by body motor dysfunction due to dopaminergic reduction in the central nervous system. Freezing of gait is a motor disorder that affects certain Parkinson's disease patients. However, it is hypothesized that non-motor functions mediated by the cholinergic system are also involved in developing freezing of gait. Visual information processing speed, or inspection time is independent of the motor response, and can be used a reliable measure of the cholinergic system integrity.

Objective

Inspection time can be used to investigate whether Parkinson's disease patients with freezing of gait symptoms have a larger impairment in cholinergic mediated functions than those patients who have no freezing of gait symptoms and healthy controls.

Methods

The inspection time was determined by a simple length discrimination task. Twenty-two Parkinson's disease patients with freezing of gait, 25 Parkinson's disease patients without freezing of gait, and 25 aged matched healthy controls participated in the study.

Results

Based on the log values of IT score, Parkinson's disease patients with freezing of gait symptoms had statistically significant slower inspection times (mean of 1.793 ms) than Parkinson's disease patients without freezing of gait (mean of 1.655 ms) and healthy controls (mean of 1.523 ms). Inspection times for the Parkinson's disease patients without FOG symptoms were also significantly slower than healthy controls.

Conclusion

The results of this study support the hypothesis that the cholinergic system integrity is affected more in Parkinson's disease patients with freezing of gait symptoms.

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Non-motor symptoms are associated with Parkinson’s disease patients.

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Inspection time can be used as a reliable tool to evaluate the integrity of the cholinergic system.

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Patients with Parkinson’s disease especially those who showed freezing of gait symptoms had longer inspection time score which suggest they have deficit in the cholinergic system.

Correlates and stability of alternate stimuli in a computer-based measure of inspection time

Inspection time tasks assess the ability to make a simple visual discrimination, typically in milliseconds. Typically, IT stimuli consists of a pi-shaped figure, in which subjects select the side with the significantly longer leg. To prevent storage in iconic memory, a backward mask is then introduced. However, some participants have reported that the mask may cause the shorter leg to appear to lengthen, creating a possible strategy that facilitates performance. As a result, alternative stimuli/masks have been developed; however, these alternative stimuli may be processed differently. This study assessed the cognitive correlates and stability of an alternative stimuli/mask. Results indicated that processing of the stimuli was influenced by an interaction between the complexity of the stimuli and the number of times it was presented. Specifically, the alternative stimulus/mask produced slower processing, particularly at the time of a second administration; however, it contributed an important and unique relationship with speeded, general intelligence.

Velocidade de processamento da informação na definição e avaliação da inteligência

A relação entre os tempos de reação em tarefas simples e complexas, ou os tempos de inspeção, e os resultados em testes de inteligência tem sido analisada ao longo dos tempos. Neste artigo descrevem-se os procedimentos usados na avaliação dos tempos de reação e tempos de inspeção, apresentam-se os coeficientes de correlação que tais tarefas mantêm com os testes de inteligência, assim como algumas das explicações avançadas pelos autores para os dados obtidos. Mesmo que os índices de correlação oscilem em função da natureza das tarefas, e sobretudo do grau de homogeneidade ou heterogeneidade das amostras avaliadas, os estudos apontam, de uma forma sistemática, para correlações negativas e estatisticamente significativas. No entanto, o grande desafio para esta linha de investigação continua a ser a construção e testagem de uma teoria psicológica explicativa dos coeficientes obtidos.

Effects of caffeine in non-withdrawn volunteers

RATIONALE

Evidence for the behavioural effects of caffeine is prevalent in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. However, there is an on-going debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of caffeine withdrawal. Using participants who had consumed their normal daily quota of caffeine this study alleviated this potential confound as all participants were not withdrawn at the time of testing.

OBJECTIVES

To determine whether caffeine influenced the mood and performance of non-withdrawn volunteers.

METHODS

Sixty eight volunteers, all of whom were regular caffeine consumers, consumed their normal amount of caffeine over the course of the day. Baseline measures of mood and performance were then carried out followed by double-blind administration of caffeine (2 mg/kg) or placebo. The test battery was repeated again 30 min after ingestion of the drink.

RESULTS

Our findings showed improvements comparable to previous research. Mood was improved and performance on a number of cognitive measures was improved. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.

CONCLUSIONS

This study provided evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative withdrawal effects.

The functional anatomy of inspection time: an event-related fMRI study

Twenty healthy young adults underwent functional magnetic resonance imaging (fMRI) of the brain while performing a visual inspection time task. Inspection time is a forced-choice, two-alternative visual backward-masking task in which the subject is briefly shown two parallel vertical lines of markedly different lengths and must decide which is longer. As stimulus duration decreases, performance declines to chance levels. Individual differences in inspection time correlate with higher cognitive functions. An event-related design was used. The hemodynamic (blood oxygenation level-dependent; BOLD) response was computed as both a function of the eight levels of stimulus duration, from 6 ms (where performance is almost at chance) to 150 ms (where performance is nearly perfect), and a function of the behavioral responses. Random effects analysis showed that the difficulty of the visual discrimination was related to bilateral activation in the inferior fronto-opercular cortex, superior/medial frontal gyrus, and anterior cingulate gyrus, and bilateral deactivation in the posterior cingulate gyrus and precuneus. Examination of the time courses of BOLD responses showed that activation was related specifically to the more difficult, briefer stimuli and that deactivation was found across most stimulus levels. Functional connectivity suggested the existence of two networks. One comprised the fronto-opercular area, intrasylvian area, medial frontal gyrus, and the anterior cingulate cortex (ACC), possibly associated with processing of visually degraded percepts. A posterior network of sensory-related and associative regions might subserve processing of a visual discrimination task that has high processing demands and combines several fundamental cognitive domains. fMRI can thus reveal information about the neural correlates of mental events which occur over very short durations.

Visual inspection time in Parkinson’s disease: deficits in early stages of cognitive processing

Inspection time (IT) is a simple information processing paradigm dependent on a participant's ability to identify physical properties of a stimulus presented for a specified time interval. In contrast with reaction time (RT) studies, the dependent variable of interest in IT is not related to the motoric speed with which the individual is able to respond, but rather the minimum presentation time necessary for participants to reliably identify physical properties of the stimulus. It is well documented that individuals with Parkinson's disease (PD) experience significant impairment on tests of simple RT, but it is unclear whether such deficits can be interpreted as 'pure' slowness of information processing, or a delay in the selection and output of a motor response. In the first experiment described here, a sample of 'optimally medicated' PD patients was compared with an age-matched control group, on an IT task. Results of this experiment suggested that individuals with PD required significantly longer stimulus presentation times than healthy participants. The second experiment compared a sample of PD patients (tested both "ON" and "OFF" their typical dopaminergic medications), with an age-matched control group, on the same test of IT. Results again indicated a significant IT deficit in participants with PD, and suggested that these deficits do not significantly resolve with levodopa treatment. Overall, the results of these two experiments suggest that information processing deficits associated with PD are distinct from motor impairment. These findings are further discussed in terms of existing neurochemical models of information processing ability.

Human intelligence differences: towards a combined experimental-differential approach

Despite the fact that much is known about the taxonomy and predictive validity of human intelligence differences, there has been relatively little progress in understanding their cognitive bases. However, some recent firm findings mark the beginnings of a cognitive reductionism in human intelligence. Progress towards discovering 'cognitive components' that, firstly, show individual differences and, secondly, relate to psychometric intelligence differences is described here at different nominal levels of analysis: 'psychometric', 'cognitive-experimental' and 'psychophysical'. The field of intelligence differences remains a fertile yet seriously under-developed demesne in which cognitive scientists should collaborate with differential psychologists.