Nadège Doignon-Camus

Vigilance and intrinsic maintenance of alert state: An ERP study.

To better understand the involvement of the progressive increase in low-frequency bands in the intrinsic maintenance of the alert state, we assessed the effects of time on the processes expressed in broad-band event-related potentials (ERPs) at play during a test of sustained attention. In this test, the fixed sustained attention to response task (SART) paradigm, a predictable series of single digits are presented (1-9) and subjects are required to make a response to each number (go trials) with the exception of the number 3 (no-go trial). Our results show that vigilance decline, reflected by significant changes in performance and spectral power, is accompanied by specific effects of time on the P2 and Late Positive 1 (LP1) components. The digit 2 is an upcoming cue for the critical target trial, which serves as an important marker for alert response during the task. From this perspective, the amplitude decrease of the P2 (on digit 2 exclusively) with time-on-task could be the concomitant in ERPs of the failures to observe and to attend the critical digit 3. The increase in the amplitude of the later positive component (LP1) from the first period to the last period, could be viewed as a measure of resource allocation, of the higher redeployment of effort towards the task. The progressive deterioration of vigilance level, which results in performance decline and low-frequency activity increase, could thus be a direct consequence of the failure to maintain an intrinsic alert state with time-on-task, despite the larger resource allocation deployed by the participant towards task completion.

Impaired visual expertise for print in French adults with dyslexia as shown by N170 tuning.

Efficient reading relies on expertise in the visual word form area, with abnormalities in the functional specialization of this area observed in individuals with developmental dyslexia. We have investigated event related potentials in print tuning in adults with dyslexia, based on their N170 response at 135-255 ms. Control and dyslexic adults performed a lexical decision task with symbol strings and four sets of word-like stimuli (consonant strings, pseudowords, low frequency words and high frequency words). N170 tuning was observed in the control group, with larger left occipito-temporal negativities for word-like stimuli than for symbol strings. In contrast, N170 specialization was lacking in dyslexics, suggesting no visual expertise for print. Moreover, behavioral data indicated that adults with dyslexia had longer latencies and more errors for pseudowords than for other stimuli, suggesting a persistent phonological deficit in these individuals. These findings suggest that altered decoding abilities may disrupt perceptual expertise for print. The results are discussed in the context of the phonological mapping deficit theory.

Impact of motivation on cognitive control in the context of vigilance lowering: an ERP study.

We assessed the effects of time-on-task on cognitive control expressed by the CRN/Nc and the extent to which motivation modulates this relationship. We utilized two groups of participants, who were told that their performance would (evaluation condition) or would not (control condition) be evaluated online. Both groups performed a version of the Eriksen Flanker Task for 60 min. We observed classical vigilance lowering, manifested by a progressive performance decline with time-on-task, in the control, but not in the evaluation, condition. In the latter, performance remained stable throughout the task. ERP analysis indicated the same interaction in our main component of interest, the CRN/Nc, whose amplitude decreased from the first to the last period in the control condition but remained stable over time in the evaluation condition. To our knowledge, this study is the first to demonstrate the impact of motivation on monitoring processes as indexed by the correct response negativity, in the context of a prolonged task. Vigilance lowering caused by a repetitive and prolonged flanker task, results in compromised response control and compromised control of correct responses. Our results suggest that alterations in ACC functioning may underlie vigilance decline and can be viewed as evidence that the action monitoring functions of the ACC can be positively affected by motivation.

Sustained attention in the elderly: what do we know and what does it tell us about cognitive aging?

The ability to achieve and maintain the focus of cognitive activity on a given stimulation source or task, in other words to sustain attention or vigilance, is a fundamental component of human cognition. Given the omnipresent need for sustained attention in peoples daily lives, a precise knowledge of the effects of normal aging on sustained attention is crucial. Findings in this topic are currently not consistent since they highlight either alteration or preservation or even the two, depending on the experimental approach used. Actually, the two existing approaches do not involve bottom-up and top-down processes at the same extent, which may in part account for this inconclusiveness. This review presents and attempts to explain these results by putting them into perspective with our current knowledge on cognitive aging and the two competing vigilance decrement theories, and discusses how they could inform us on our problems with sustaining attention over time.

Investigating sustained attention ability in the elderly by using two different approaches: Inhibiting ongoing behavior versus responding on rare occasions

Previous studies on sustained attention ability in the elderly produced inconsistent results. The aim of this study was to evaluate sustained attention performance in younger and older individuals by using, in a within-subjects design, two versions of the same task (the sustained attention to response task, SART) in which only in the response mode differed: in a traditionally formatted task (TFT), subjects had to respond to rare targets, and in a Go/No-Go task they had to withhold response to rare targets. Results showed that in the TFT SART only the older group exhibited a vigilance decrement. On the contrary, only young individuals showed a vigilance decrement in the Go/No-Go SART. These results showed that older individuals, who also reported less mind wandering and a higher level of motivation, exhibited preserved sustained attention ability in the Go/No-Go SART, which could be explained by increased engagement of cognitive control mechanisms in this population. The discrepancy in performance depending on the approach used also underlines the need for further studies on the nature of attention failures and their underlying mechanisms.

The Effects of Aging on Sustained Attention Ability: An ERP Study

The aim of this study was to investigate the effects of aging on inhibitory processes and attentional resources in a long-lasting Go/No-Go sustained attention task using the event-related potential (ERP) technique. In line with recent studies, our results showed that older adults were able to maintain sustained attention performance throughout the duration of the task, whereas younger subjects exhibited a vigilance decrement. Regarding ERP results, older adults had larger P2 and Go-P3 amplitudes, components related to resource allocation, suggesting that the older subjects invested more resources in task performance. In addition, the No-Go P3 component, related to inhibitory processes, was more frontally distributed in older than in younger participants. This age-related frontal scalp overrecruitment may have played a compensatory role, enabling older subjects to perform better than younger subjects throughout the duration of the task.

Age-related differences in the recruitment of proactive and reactive control in a situation of sustained attention

We examined ERP indices of proactive and reactive cognitive control processes in younger and older adults performing a sustained attention Go/No-Go task. Behavioral results showed that older adults were able to maintain a stable level of performance over time, while younger adults exhibited a vigilance decrement. The main ERP findings showed that in older adults, the amplitude of the pre-stimulus slow wave, a marker of proactive control, remained stable with time on task, and that the amplitude of the sustained potential, a marker of reactive control, increased with time on task. On the other hand, in younger adults, the amplitudes of both components decreased over time. Overall, older participants also exhibited larger amplitudes of the error negativity than their younger counterparts. These results suggest that age-related differences in the recruitment of proactive and reactive control over the course of the task can explain age differences in sustained attention performance.

Can we see syllables in monosyllabic words? A study with illusory conjunctions

Mathey, Zagar, Doignon, and Seigneuric (2006) reported an inhibitory effect of syllabic neighbourhood in monosyllabic French words suggesting that syllable units mediate the access to lexical representations of monosyllabic stimuli. Two experiments were conducted to investigate the perception of syllable units in monosyllabic stimuli. The illusory conjunction paradigm was used to examine perceptual groupings of letters. Experiment 1 showed that potential syllables in monosyllabic French words (e.g., BI in BICHE) affected the pattern of illusory conjunctions. Experiment 2 indicated that the perceptual parsing in monosyllabic items was due to syllable information and orthographic redundancy. The implications of the data are discussed for visual word recognition processes in an interactive activation model incorporating syllable units and connected adjacent letters (IAS; Mathey et al., 2006).

Is the impaired N170 print tuning specific to developmental dyslexia? A matched reading-level study with poor readers and dyslexics.

Left N170 print tuning has been associated with visual expertise for print and has been reported to be impaired in dyslexics, using age matched designs. This is the first time N170 print tuning has been compared in adult dyslexics and adult poor readers, matched in reading level. Participants performed a lexical decision task using both word-like stimuli and symbol strings. In contrast to dyslexics, poor readers displayed similar N170 tuning to control expert readers, suggesting that impaired N170 specialization is a hallmark of developmental dyslexia. Our findings provide electrophysiological support for dyslexia being the result of abnormal specialization of the left occipito-temporal areas involved in the expert processing of print. Furthermore, as shown by correlations data and in accordance with the phonological mapping deficit theory, the impaired visual expertise for print described in dyslexics may have been caused by their core phonological deficits.

Conflict control processing in adults with developmental dyslexia: an event related potentials study.

OBJECTIVEnThe present study investigated the time course for processing conflict in dyslexic adults using a flanker task.nnnMETHODSnSixteen dyslexic and 15 control adults performed a flanker task comprising congruent and incongruent trials in which participants had to indicate the direction of targets surrounded by flankers. Early negative potentials associated with orienting of attention (i.e., N1) and conflict monitoring (i.e., N2) and two positive potentials associated with conflict resolution (i.e., P3b and Nogo P3) were recorded.nnnRESULTSnThe behavioral data showed differences between incongruent and congruent trials for reaction times in both groups but for error rate only in dyslexics. As in previous studies, controls displayed greater N1, N2 and NoGo P3 as well as a smaller P3b in incongruent trials. Dyslexics lacked N1, N2 and P3b modulation whereas NoGo P3 effect was preserved.nnnCONCLUSIONnDyslexics showed impairments in conflict monitoring and in some aspects of conflict resolution (i.e., the allocation of attentional resources) whereas other aspects of conflict resolution (i.e., the inhibition) were preserved.nnnSIGNIFICANCEnThis is the first study to investigate conflict control processing in dyslexic adults using ERPs. Results provide evidence for deficits in orienting of attention, conflict monitoring and allocation of attentional resources in dyslexics.