Spatial Inhibition of Return promotes changes in response-related mu and beta oscillatory patterns.

The possible role that response processes play in Inhibition of Return (IOR), traditionally associated with reduced or inhibited attentional processing of spatially cued target stimuli presented at cue-target intervals longer than 300 ms, is still under debate. Previous psychophysiological studies on response-related Electroencephalographic (EEG) activity and IOR have found divergent results. Considering that the ability to optimize our behavior not only resides in our capacity to inhibit the focus of attention from irrelevant information but also to inhibit or reduce motor activation associated with responses to that information, it is conceivable that response processes are also affected by IOR. In the present study, time-frequency (T-F) analyses were performed on EEG oscillatory activity between 2 and 40 Hz to check whether spatial IOR affects response preparation and execution during a visuospatial attention task. To avoid possible spatial stimulus-response compatibility effects and their interaction with the IOR effects, the stimuli were presented along the vertical meridian of the visual field. The results differed between lower and upper visual fields. In the lower visual field spatial IOR was related to a synchronization in the pre-movement mu band at bilateral precentral and central electrodes, and in the post-movement beta band at contralateral precentral and central electrodes, which may be associated with an attention-driven reduction of somatomotor processing prior to the execution of responses to relevant stimuli presented at previously cued locations followed by a post-movement deactivation of motor areas. In the upper visual field, spatial IOR was associated with a decrease in desynchronization around response execution in the beta band at contralateral postcentral electrodes that might indicate a late (last moment) reduction of motor activation when responding to spatially cued targets. The present results suggest that different response processes are affected by spatial IOR depending on the visual field where the target is presented.

Age-related occipito-temporal hypoactivation during visual search: relationships between mN2pc sources and performance.

Recently, an event-related potential (ERP) study (Lorenzo-López et al., 2008) provided evidence that normal aging significantly delays and attenuates the electrophysiological correlate of the allocation of visuospatial attention (N2pc component) during a feature-detection visual search task. To further explore the effects of normal aging on the N2pc neural sources, neuromagnetic activity during the execution of a visual search task was recorded in healthy young (N=14) and older (N=20) participants by using magnetoencephalography (MEG). The possible relationships between these neural sources and overt performance were explored by assessing the co-variation between the neural N2pc activity and both the task performance and the execution in the Trail Making Test Form A (TMT-A). Results revealed that young participants showed greater activity in occipito-temporal regions than older participants during the mN2pc (magnetic counterpart of the N2pc component) latency range (190-270ms). Moreover, older participants showed reduced relative activation in the right occipito-temporal source of mN2pc. These findings suggest that the previously observed age-related changes in N2pc parameters are associated with a significant hypoactivation of occipito-temporal N2pc sources that is more marked in the right hemisphere.

Visual target processing in high- and low-performing older subjects indexed by P3 component.

AIM: To explore the possible changes in the parameters of the P3 event-related potential (ERP) component among groups of young and older healthy subjects characterized as either high- or low-performers in a visual attention task. METHODS: Both conventional and single-trial analyses of the visual P3 component were performed on each group of subjects. RESULTS: P3 component significantly increased in latency as a function of age. The high-performing older subjects showed the posterior predominance of P3, as in young subjects. However, the low-performing older subjects showed a significant P3 amplitude reduction at posterior locations and topographically more widespread activity. Furthermore, single-trial analysis showed that low-performing older subjects presented higher intertrial variability in P3 latency, few trials with P3 generation, and a reduced P3 amplitude in these trials in whom P3 was generated. CONCLUSION: These data suggest a specific decline in visual target processing in the low-performing older subjects, which would imply a reduction in these attentional brain resources that are allocated to correctly select the relevant stimuli. The implications of this finding for the actual compensation versus dedifferentiation debate in normal aging are discussed.

Modulations of the visual N1 component of event-related potentials by central and peripheral cueing.

OBJECTIVE: The aim of this study is to investigate the effects of the central and peripheral cueing on N1 component of the event-related potentials (ERPs) and the time course of these effects. METHODS: ERPs were recorded while participants performed a discrimination task on the height of target bars, which were presented after informative-central, informative-peripheral or uninformative-peripheral cues with stimulus onset asynchronies (SOAs) of 100, 300, 500 or 700 ms. RESULTS: Peripheral cues (informative and uninformative) elicited stronger effects of cue validity on N1 300 ms after cue onset, whereas central cues led to a more sustained validity effect on N1, with later stronger effects, at 500 ms SOA. CONCLUSIONS: The present data showed that central and peripheral cues affected to the level of processing reflected by the N1 component, but there were differences in the time course of these effects. Attentional orienting in response to central cueing resulted in a sustained validity effect on N1, relative to the more transitory activation of the process reflected by the N1 validity effect in this peripheral cueing task. SIGNIFICANCE: This study provides a detailed within-subject analysis of the time course of the effects of central and peripheral cueing on N1.

Automatic detection of motion direction changes in the human brain.

The possibility that the visual system is able to register unattended changes is still debated in the literature. However, it is difficult to understand how a sensory system becomes aware of unexpected salient changes in the environment if attention is required for detecting them. The ability to automatically detect unusual changes in the sensory environment is an adaptive function which has been confirmed in other sensory modalities (i.e. audition). This deviance detector mechanism has proven to be based on a preattentive nonrefractory memory-comparison process. To investigate whether such automatic change detection mechanism exists in the human visual system, we recorded event-related potentials to sudden changes in a biologically important feature, motion direction. Unattended sinusoidal gratings varying in motion direction in the peripheral field were presented while subjects performed a central task with two levels of difficulty. We found a larger negative displacement in the electrophysiological response elicited by less frequent stimuli (deviant) at posterior scalp locations. Within the latency range of the visual evoked component N2, this differential response was elicited independently of the direction of motion and processing load. Moreover, the results showed that the negativity elicited by deviants was not related to a differential refractory state between the electrophysiological responses to frequent and infrequent directions of motion, and that it was restricted to scalp locations related to motion processing areas. The present results suggest that a change-detection mechanism sensitive to unattended changes in motion direction may exist in the human visual system.

The time course of the effects of central and peripheral cues on visual processing: an event-related potentials study.

OBJECTIVE: The varying results of visual event-related potential (ERP) studies of central and peripheral cueing suggest that these types of cue may modulate stimuli processing with different time courses. The aim of this study was to investigate differences in the time course of facilitatory effects on the visual processing induced by peripheral and central cues. METHODS: ERPs were recorded for visual target stimuli that were preceded by informative-central, informative-peripheral or uninformative-peripheral cues with stimulus onset asynchronies (SOAs) of 100, 300, 500 or 700 ms. RESULTS: Validly cued stimuli elicited an enhanced P1 component with peripheral cueing at 100 ms SOA. P1 amplitude in valid trials was reduced at 300, 500 and 700 ms SOAs with uninformative-peripheral cueing, but only at 500 ms SOA with informative-peripheral cueing. With informative-central cueing, there was no validity effect on P1. CONCLUSIONS: These results suggest that the automatic attraction of attention by a peripheral cue results in improved sensory processing at the cued location. This facilitation is replaced by an inhibitory effect when SOA increases, although cue informativeness may modulate this effect. Central cueing does not affect sensory processing at the P1 level.

MMN in the visual modality: a review.

The mismatch negativity (MMN) component is an event-related potential (ERP) that can be elicited by any change in the acoustic environment, and it is related to memory-based, automatic processing mechanisms, and attentional capture processes. This component is well defined in the auditory modality. However, there is still a great controversy about its existence in the visual modality. This paper reviews the studies that are relevant with regard to memory-based, automatic deviance detection ERPs in the visual system. The paper discusses the main strengths and limitations of those studies and suggests what directions should be taken for future research.

The accuracy of sound duration representation in the human brain determines the accuracy of behavioural perception.

In recent years, the links between neural activity and perception have been an area of interest in cognitive neuroscience. Combined psychophysiological and psychophysical experiments provide a new powerful tool for establishing the relationship between neural activity and perceptual performance. In animals, intracellular recordings combined with psychophysical detection indices have revealed that a particular neuron or set of neurons can play a critical role in the generation of a perceptual event, showing detection functions (referred to as neurometric functions) which are remarkably similar to psychophysical detection functions, or psychometric functions (Parker & Newsome, (1998) Annu. Rev. Neurosci. , 21, 227-277). As noninvasive techniques for recording neural activity are now available, studies combining neuroelectric and psychophysical measures in humans are sparse. In the present study, the accuracy of the human brain in detecting differences in sound duration and the subject's ability to perceive the same differences were tested by means of mismatch negativity (MMN) and the distance between the distributions of false alarms and hits (sensitivity index d'), respectively. It was found that the accuracy of the human auditory system to represent sound duration information is related to the duration context in which the sounds are heard, and that these contextual representations determine the accuracy of perception at the behavioural level.

Ageing-related changes in the processing of attended and unattended standard stimuli.

Responses to standard stimuli presented during a dichotic listening task were analysed in 53 healthy subjects from 20 to 86 years of age. The aim was to determine whether N1 and P2 waves showed changes attributable to attention or more general changes underlying the electrophysiological processing of such stimuli under attended and unattended conditions. N1 was larger at midline frontal and central electrodes in middle-aged and in elderly subjects without changes in its topographical distribution. These changes were independent of attention. P2, which was also larger in middle-aged and in elderlies, showed scalp distribution changes depending on the direction of attention. The present results indicate the existence of general ageing-related changes in the processing of attended and unattended standard stimuli which may be related to inhibitory deficits (N1) and to changes in the orientation of electrical sources (P2).

Ageing effects on flash visual evoked potentials (FVEP) recorded from parietal and occipital electrodes.

The effects of ageing on flash visual evoked potentials (FVEP) recorded from 6 posterior parietal and occipital sites were studied in a sample of 73 healthy subjects of between 20 and 86 years of age. Latencies of components P1, N1 and P2, and amplitudes of components P1 and P3 increased linearly with age at all emplacements. The results obtained from occipital electrodes are in line with previous reports and additionally show that i) the effects of age constantly increase over time, and ii) age affects not only the early but also the later components (> 150 ms) of the FVEP. The overall pattern of results suggests that elderly subjects show slower transmission of visual information and deficiencies in the inhibitory regulation of activity generated during the arrival of repetitive non-attended visual stimulation. The findings with parietal electrodes show that ageing effects are more marked at these emplacements than at occipital electrodes. Furthermore, this raises the question of a possible differential involvement of primary and nonprimary visual cortex by age, but this hypothesis can only be explored with high-intensity multichannel recordings and dipolar modelling.

Aging-related changes in processing of non-target and target stimuli during an auditory oddball task.

A total of 73 healthy subjects aged 20-86 years performed an auditory 'oddball' task. The age-dependence of N1 and P2 elicited by non-target stimuli, of N2 and P3 elicited by target stimuli and of N2a and N2b components (target minus non-target difference waves) was investigated across 20 electrodes to detect any aging-related changes in the psychophysiological processing of such stimuli during the task. Aging-related differences in within-task changes in non-target ERPs were also investigated. In non-target ERPs, it was found that P2 amplitude at Fz increased linearly with advancing age and the analysis of within-task changes indicated that P2 amplitude decreased during the task in young subjects at Pz, but remained unchanged in middle-aged and elderly subjects. These results suggest the existence of aging-related inhibitory deficits that may hinder the disengagement of attentional resources from irrelevant stimuli during the task. In the target ERPs, the latencies of N2 and P3 increased linearly at Fz, Cz and Pz. The increases in N2 were mainly due to linear increases in N2b latency at Fz, Cz and Pz, indicating that the aging-related slowing begins at controlled memory comparison of non-target/target stimuli. P3 amplitude presented a more uniform scalp distribution in middle-aged and in elderly subjects and pnly decreased significantly with advancing age in men, which may explain the divergent results in the literature on aging-related changes of P3 amplitude.

Automatic and effortful processes in auditory memory reflected by event-related potentials. Age-related findings.

Mismatch negativity (MMN) and N2b were elicited during a selective dichotic-listening task in 16 young (Y), 16 middle-aged (M) and 19 elderly (E) subjects to evaluate automatic and effortful memory comparison of auditory stimuli. Sequences of standard (80%) and deviant (20%) tones were dichotically presented to subjects in two runs. In each run, subjects were instructed to give a button-press response to the deviant (target) tones in the ear designated as attended and to ignore the input to the other ear. Peak latencies, peak amplitudes and mean amplitudes were calculated for MMN and N2b components in each subject. MMN latency and amplitude were quite stable regardless of age, while N2b latency was significantly longer in M and E subjects than in Y subjects. These results are interpreted as reflecting that automatic processes of comparison in auditory memory of stimuli presented at short interstimulus intervals remain quite stable from 23 to 77 years of age; however, those requiring attentional effort decline with age.

Effects of aging on middle-latency auditory evoked potentials: a cross-sectional study.

BACKGROUND: The results of previous studies comparing the middle-latency auditory evoked potentials (MAEPs) of young and elderly subjects have suggested that thalamic inhibitory deficits underlie age-related increases in MAEP amplitudes. METHODS: MAEPs were recorded from 73 healthy subjects aged between 20 and 86 years. The latencies of MAEPs recorded at Fz were subjected to two-way analyses of variance for the effects of age group and sex. Amplitude data were subjected to analyses of covariance with age group and sex as between-subjects factors, electrode position as within-subject factor, and individual perceptual thresholds as covariates. Variables exhibiting significant effects of age group were further investigated by regression analysis. RESULTS: Age correlated positively with Na, Na-Pa, and Nb-Pb amplitudes. The distribution of Na-Pa amplitude over the scalp varied with age. CONCLUSIONS: The observed age-related increases in amplitude are believed to reflect diminished capacity of subcortical and related cortical systems to inhibit the response to repetitive auditory stimuli that require no attentional effort. Possible age-related changes in the cortical distribution of MAEPs are also discussed.