Learning during visual search in children with attentional and learning problems: a trial to trial evaluation of RT and ERP measures.

Trial to trial Event Related Potentials (ERPs) were recorded from children with attentional problems (APs), learning problems (LPs), and from children without these problems (NCs). The task required the subjects to memorize two figures and to selectively respond to their occurrence in a series of stimuli. Stimuli consisted of a display of figures at eight locations in a circle, whereby the targets were presented at a random or a fixed location. Learning from knowledge of prior displays was possible only in the fixed condition. Learning during presentation of the fixed series was manifest in several components. A Slow Wave (SW) difference between series, initially not present, developed within seven trials, and thus corresponded to the rapidity with which the reaction times (RTs) decreased over trials. A larger occipital SW difference was discovered in AP children and a larger frontocentral one in LP children compared to normals. The latency of this SW and the P300 difference between series were delayed with about 200 msec in APs compared to NCs. The task difference in the earliest component, the P120, that increased after behavioral task acquisition was completed, was seen in normal children only. This probably reflected feature-specific (location) attentional demands, that decreased slowly in normal children when the task became more predictable following a number of trials. Task differences of the N200, possibly reflecting covert orienting of attention, were initially smaller in APs and LPs than those of NCs, but they increased in APs (and in LPs more slowly) over trials. Differences were found for parietal amplitudes of the P300 in LPs and NCs, but not for APs. We concluded that AP children show early deficits that could originate from a limited capacity in focussing attention, which in turn prolongs stimulus evaluation. All subsequent processes are delayed by a similar amount of time. In addition, the relatively small frontocentral ERP's of the AP group suggest diminished frontal functioning. Problems in task acquisition and a prolonged process of memory updating might be induced by the slow adaptation to task differences in LP's, and delayed parietal SWs during task acquisition together with a marked frontocentral distribution and no RT difference

Visual spatial attention in migraine sufferers in postictal and interictal phases: An event-related potential study.

Nine migrainers with (MWA; aged 18-36 yrs) and 10 without (MWOA; aged 21-36 yrs) aura as well as 10 controls (aged 19-28 yrs) from a female university were measured twice with an interval of 7 days. The first session of recordings and tests for migraineurs was held about 7 hours after a migraine attack. The authors hypothesized that electrophysiological changes in the posterior cerebral cortex related to visual spatial attention are influenced by the level of arousal in migraineurs with aura, and that this varies over the course of time. Event related potentials related to the active visual attention task manifested significant differences between controls and both types of migraine sufferers for the N200, suggesting a common pathophysiological mechanism for migraineurs. Furthermore, MWOAs showed a significant enhancement for the N200 at the second session, indicating the relevance of time of measurement within migraine studies. Finally, MWAs showed significantly enhanced P240 and P300 components at central and parietal cortical sites compared to MWOAs and controls, which seemed to be maintained over both sessions and could be indicative of increased noradrenergic activity in MWAs

The influence of visual information on habituation of the electrodermal and the visual orienting reaction

In this study the influence of the information value of visual stimuli on habituation of the visual orienting reaction (VOR) and the skin conductance reaction (SCR) was investigated. 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information, the other half received the conditions in the reversed order. Subjects fixated the stimuli with the higher information value longer than the stimuli with the lower information value during the 14 trials and habituated slower. This effect of information was absent in the second block and VOR habituation was also faster in this block. There was no difference in SCR amplitudes nor in SCR habituation scores between the two information conditions, neither in block 1 nor in block 2. The results of this study are discussed in relation with a two-stage model of the OR

The influence of task relevance and stimulus information on habituation of the visual and the skin conductance orienting reaction

This study investigated the hypothesis that task-relevant stimuli induce orienting reactions (ORs) that are stronger and more resistant to habituation when their information content is high than when it is low. Task-relevance was given to the stimuli by rewarding the subjects for correct recognition at the end of the experiment. The dependent variables in this study were the visual orienting reaction (VOR), the skin conductance reaction (SCR), their habituation scores and the number of spontaneous fluctuations in skin conductance (SFs). 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information condition, while the other half received the reversed order. The VOR habituated quickly and was not significantly influenced by information value. SCR amplitudes were larger and SCR-habituation slower to stimuli containing more information. The results were interpreted as supporting the hypothesis that the SCR is associated with a secondary phase of the orienting process

Eye-movements in a two-dimensional plane: A method for calibration and analysis using the vertical and horizontal EOG

A method for calibration, orthogonalization and standardization of eye movements is described. The method is based on linear transformation of the horizontal and vertical EOG. With this method it is possible to measure the locus of eye fixation on a TV screen and its associated fixation time. Because of the used time constant (TC) of 36 sec, subjects must look at the centre of the TV screen or at random places on the screen during the interstimulus intervals (ISIs). For the EOG registration pre-amplifiers with a long TC were used to cut off slow changes in polarization caused by the electrode-electrolyte combination. In the calibration procedure only four orthogonal stimulus points were used. In an experiment to evaluate this method, subjects had to fixate letters on a TV screen in 12 different pre-determined positions. The distance between the measured locus of fixation and the coordinates of the stimulus was measured. The mean horizontal errors ranged from 1.4–2.2 degrees of arc and the mean vertical errors from 2.4–3.8 degrees of arc across subjects. It was concluded that accuracy was within acceptable limits, despite the fact that eye movement behaviour during the ISI was free. It was shown that the method is insensitive to non-orthogonality of the vertical and horizontal EOG. Calibration and transformation can be done by any real time computer system. The method is suitable for measuring, e.g. the visual orienting reaction (VOR), and it can also be applied in event related potential (ERP) studies where ocular fixation is use

Learning where to look: Electrophysiological and behavioral indices of visual search in young and old subjects.

Explored 24 young (aged 18-24 yrs) and 24 elderly (aged 65-75 yrs) right-handed males' use of regularities in target location in a visual display to guide searching for targets. Although both young and elderly Ss showed efficient use of search strategies, slight differences in reaction times suggest decreased ability in elderly Ss' use of complex cues. In young Ss, P3 amplitudes were larger for trials where the rule that governed the location of the target became evident. Enhanced slow wave (SW) amplitude indicated uncertainty in random search conditions. Elderly Ss' P3 and SW amplitudes, however, seemed unrelated to behavioral performance. Results suggest that age-related differences in search tasks can be understood in terms of age-related changes in strategies of allocating visual attention