Inhibition of visual discrimination during a memory-guided saccade task

Voluntary behavior critically depends on attentional selection and short-term maintenance of perceptual information. Recent research suggests a tight coupling of both cognitive functions with visual processing being selectively enhanced by working memory representations. Here, we combined a memory-guided saccade paradigm (6-s delay) with a visual discrimination task, performed either 1,500, 2,500, or 3,500 ms after presentation of the memory cue. Contrary to what can be expected from previous studies, our results show that memory of spatial cues can transiently delay speeded discrimination of stimuli presented at remembered locations. This effect was not observed in a control experiment without memory requirements. Furthermore, delayed discrimination was dependent on the strength of actual memory representations as reflected by accuracy of memory-guided saccades. We propose an active inhibitory mechanism that counteracts facilitating effects of spatial working memory, promoting flexible orienting to novel information during maintenance of spatial memoranda for intended actions. Inhibitory delay-period activity in prefrontal cortex is a likely source for this mechanism which may be mediated by prefronto-tectal projections.     

Distractor effects on saccade trajectories: a comparison of prosaccades, antisaccades, and memory-guided saccades

The present study investigated the contribution of the presence of a visual signal at the saccade goal on saccade trajectory deviations and measured distractor-related inhibition as indicated by deviation away from an irrelevant distractor. Performance in a prosaccade task where a visual target was present at the saccade goal was compared to performance in an anti- and memory-guided saccade task. In the latter two tasks no visual signal is present at the location of the saccade goal. It was hypothesized that if saccade deviation can be ultimately explained in terms of relative activation levels between the saccade goal location and distractor locations, the absence of a visual stimulus at the goal location will increase the competition evoked by the distractor and affect saccade deviations. The results of Experiment 1 showed that saccade deviation away from a distractor varied significantly depending on whether a visual target was presented at the saccade goal or not: when no visual target was presented, saccade deviation away from a distractor was increased compared to when the visual target was present. The results of Experiments 2–4 showed that saccade deviation did not systematically change as a function of time since the offset of the target. Moreover, Experiments 3 and 4 revealed that the disappearance of the target immediately increased the effect of a distractor on saccade deviations, suggesting that activation at the target location decays very rapidly once the visual signal has disappeared from the display.

Evidence for an attentional component of inhibition of return in visual search

Inhibition of return (IOR) is typically described as an inhibitory bias against returning attention to a recently attended location as a means of promoting efficient visual search. Most studies examining IOR, however, either do not use visual search paradigms or do not effectively isolate attentional processes, making it difficult to conclusively link IOR to a bias in attention. Here, we recorded ERPs during a simple visual search task designed to isolate the attentional component of IOR to examine whether an inhibitory bias of attention is observed and, if so, how it influences visual search behavior. Across successive visual search displays, we found evidence of both a broad, hemisphere‐wide inhibitory bias of attention along with a focal, target location‐specific facilitation. When the target appeared in the same visual hemifield in successive searches, responses were slower and the N2pc component was reduced, reflecting a bias of attention away from the previously attended side of space. When the target occurred at the same location in successive searches, responses were facilitated and the P1 component was enhanced, likely reflecting spatial priming of the target. These two effects are combined in the response times, leading to a reduction in the IOR effect for repeated target locations. Using ERPs, however, these two opposing effects can be isolated in time, demonstrating that the inhibitory biasing of attention still occurs even when response‐time slowing is ameliorated by spatial priming.     

Neural processes of attentional inhibition of return traced with magnetoencephalography

Inhibition of return (IOR) is a phenomenon that involves reaction times (RTs) to a spatially cued target that are longer than RTs to an uncued target when the interval between the cue and target is prolonged. Although numerous studies have examined IOR, no consensus has yet been reached regarding the neural mechanisms responsible for it. We used magnetoencephalography (MEG) and measured the human neural responses underlying the time course of IOR, applying a typical spatial cueing paradigm. The cue-target interval was 600+/-200 ms. Three experimental conditions were employed. Cued; the cue and target were presented at the same location. Uncued; the two stimuli were presented at opposite locations. Neutral; the cue stimulus was presented bilaterally. We found differences in the amplitudes of signals in the postero-temporal and bilateral temporal areas, and peak latencies in a central area between the cued and uncued conditions. These signals were localized to the extrastriate cortex, bilateral temporal-parietal junction (TPJ), and primary motor cortex, respectively. Bilateral TPJ activities are related to the identification of salient events in the sensory environment both within and independent of the current behavioral context and may play an important role in IOR in addition to extrastriate and the primary motor cortex.     

Short-term adaptation of the cervico-ocular reflex

Inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. IOR is typically investigated using a cue-target design, in which subjects respond only to the second stimulus of a pair. In such tasks, the measurement of true IOR may be confounded by the effect of non-ocular response inhibition, because the participant must suppress any tendency to respond (e.g. key press) to the first stimulus. This confound may be eliminated using a target-target design, in which responses are made to both stimuli. We assessed the contribution of non-ocular response inhibition to visual IOR, measured in a cue-target task, by testing participants on both cue-target and target-target detection tasks, with identical timings and stimuli. Significant IOR was obtained in both tasks but, at a stimulus onset asynchrony (SOA) of 1,400 ms, IOR magnitude was significantly greater in the cue-target condition than in the target-target condition. However, at an SOA of 1,800 ms, there was no significant difference in the magnitude of IOR between the two tasks. Thus, a proportion of the total IOR effect observed in visual cue-target tasks can be attributed to non-ocular response inhibition, but this process appears to decay more rapidly than does true IOR, having dissipated by 1,800 ms following cue onset.     

Inhibition of return and response repetition within and between modalities

Inhibition of return (IOR) refers to slower responding to stimuli at previously occupied spatial locations. IOR has been vigorously studied because of its possible deep involvement with attention mechanisms. Although IOR occurs both within and across modalities in several experimental paradigms for simple stimulus detection tasks, it has sometimes been difficult to demonstrate in perceptual discrimination tasks. In the preferred target-target paradigm, in which responses are made to a series of targets that vary in spatial location, failure to find IOR could possibly result from mixing of spatial IOR with the facilitating effects of stimulus and/or response repetition on discrimination response times. In this paper we report the first demonstration of auditory/auditory and cross-modality IOR in a target-target paradigm using a discrimination task. Our results show that IOR occurs in this task only on trials on which stimuli and responses are not repeated. These findings present a challenge to purely visual accounts of IOR and support the view that IOR arises within a more general, supra-modal mechanism of attention.     

On the distribution of attention in a visuo-manual adaptation task

We have observed in a previous study that adaptation to reversed visual feedback in a tracking task is better when subjects are instructed to look at the cursor providing feedback (group C) rather than at the target (group T). Since both groups actually looked at the target, irrespective of their instructions, we suggested that the advantage of group C is not related to their eye movements, but rather to their allocation of spatial attention. The present study scrutinized this view by combining the same adaptation task with a concurrent reaction-time task, designed to spread subjects’ attention across the whole display area. Again, subjects were instructed to look at the cursor or at the target, and again, both groups actually looked at the target. Adaptation was similar to group T, and poorer than group C of the previous study. We therefore concluded that adaptation indeed depends on the subjects’ allocation of attention: focussing attention mainly on the target, or spreading it across the whole display area, is not as good as distributing attention between target and cursor.     

Relation of frontal eye field activity to saccade initiation during a countermanding task

The countermanding (or stop signal) task probes the control of the initiation of a movement by measuring subjects’ ability to withhold a movement in various degrees of preparation in response to an infrequent stop signal. Previous research found that saccades are initiated when the activity of movement-related neurons reaches a threshold, and saccades are withheld if the growth of activity is interrupted. To extend and evaluate this relationship of frontal eye field (FEF) activity to saccade initiation, two new analyses were performed. First, we fit a neurometric function that describes the proportion of trials with a stop signal in which neural activity exceeded a criterion discharge rate as a function of stop signal delay, to the inhibition function that describes the probability of producing a saccade as a function of stop signal delay. The activity of movement-related but not visual neurons provided the best correspondence between neurometric and inhibition functions. Second, we determined the criterion discharge rate that optimally discriminated between the distributions of discharge rates measured on trials when saccades were produced or withheld. Differential activity of movement-related but not visual neurons could distinguish whether a saccade occurred. The threshold discharge rates determined for individual neurons through these two methods agreed. To investigate how reliably movement-related activity predicted movement initiation; the analyses were carried out with samples of activity from increasing numbers of trials from the same or from different neurons. The reliability of both measures of initiation threshold improved with number of trials and neurons to an asymptote of between 10 and 20 movement-related neurons. Combining the activity of visual neurons did not improve the reliability of predicting saccade initiation. These results demonstrate how the activity of a population of movement-related but not visual neurons in the FEF contributes to the control of saccade initiation. The results also validate these analytical procedures for identifying signals that control saccade initiation in other brain structures.

Spatial attention triggered by unimodal, crossmodal, and bimodal exogenous cues: a comparison of reflexive orienting mechanisms

The aim of this study was to establish whether spatial attention triggered by bimodal exogenous cues acts differently as compared to unimodal and crossmodal exogenous cues due to crossmodal integration. In order to investigate this issue, we examined cuing effects in discrimination tasks and compared these effects in a condition wherein a visual target was preceded by both visual and auditory exogenous cues delivered simultaneously at the same side (bimodal cue), with conditions wherein the visual target was preceded by either a visual (unimodal cue) or an auditory cue (crossmodal cue). The results of two experiments revealed that cuing effects on RTs in these three conditions with an SOA of 200 ms had comparable magnitudes. Differences at a longer SOA of 600 ms (inhibition of return for bimodal cues, Experiment 1) disappeared when catch trials were included (in Experiment 2). The current data do not support an additional influence of crossmodal integration on exogenous orienting, but are well in agreement with the existence of a supramodal spatial attention module that allocates attentional resources towards stimulated locations for different sensory modalities.     

Interaction between location- and frequency-based inhibition of return in human auditory system

Using a cue–target paradigm, this study investigated the interaction between location and frequency information processing in human auditory inhibition of return (IOR). The cue and the target varied in terms of location and frequency and participants were asked to perform a target detection, localization or frequency discrimination task. Results showed that, when neither location nor frequency of auditory stimuli was particularly relevant to the target detection task, there was a location-based IOR only if the cue and the target were identical in frequency and there was a frequency-based IOR only if the cue and the target were presented at the same location. When a particular feature of auditory stimuli, whether location or frequency, was directly relevant to the current task, the IOR effect was evident for this feature only if the cue and the target differed on the task-irrelevant feature, while the IOR effect was eliminated for the task-relevant feature when the cue and the target had the same task-irrelevant feature. Similarly, the IOR effect based on the task-irrelevant feature was evident when the cue and the target differed on the task-relevant feature, and was eliminated or reversed when the cue and the target shared the task-relevant feature. Theoretical implications of these findings for auditory IOR are discussed.     

A study on the neural mechanism of inhibition of return by the event-related potential in the Go/NoGo task

Inhibition of return (IOR) is a slowed response to a stimulus at recently cued locations when stimulus-onset asynchronies (SOAs) are longer than 250ms. Using an uninformative peripheral cued Go/Nogo (commit/withdrawal response) task experiment, this study aimed to characterize the neural mechanism of IOR by studying not only the early event-related potentials (ERPs), P1 and N1, but also the late ERPs, Go/Nogo-N2 and P3. Scalp topographies and LORETA showed that the changes in P1 and N1, the cueing effects, were distributed mainly over the dorsal occipito-parietal areas, such as the bilateral middle occipital gyrus and the occipital portion of the cuneus. The changes in the late Nogo-N2 and P3 were distributed mainly over frontal-central areas, such as the right medial frontal gyrus. The Nogo-N2 was smaller and earlier in valid trials than in invalid trials, suggesting that the late component related to IOR was modulated by response preparation inhibition. The Nogo-P3 was larger and later in valid trials than in invalid trials, perhaps indicating that the control system (FEF) was free from an inhibitory marker in the cued locations. These data support a mechanism of IOR consisting of both sensory inhibition and response preparation inhibition.     

Reduced intracortical inhibition during the foreperiod of a warned reaction time task

Reaction time (RT) is shortened when the response signal is preceded by a warning signal, a finding that has been attributed to response preparation during the foreperiod between the warning and response signals. Research suggests an increased excitability of cortical movement representations associated with response preparation during the foreperiod of a warned RT task (Davranche et al. in Eur J Neurosci 25:3766–3774, 2007). However when the foreperiod duration is short and constant, the motor evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation (TMS) during the foreperiod is suppressed (Touge et al. in Clin Neurophysiol 111:1216–1226, 1998), suggesting a competing inhibitory process. Three experiments measured MEP amplitude and intracortical inhibition during the foreperiod of a warned RT task in which the response was a flexion of the right index finger. Experiments 1 and 2 measured short-interval intracortical inhibition (SICI) with paired TMS pulses separated by inter-stimulus intervals (ISIs) of 3 (SICI₃) and 1.5 ms (SICI_1.5), respectively. Experiment 3 measured long-interval intracortical inhibition (LICI) with paired TMS pulses with an ISI of 100 ms (LICI₁₀₀). In all experiments MEP amplitude was smaller in the warned condition than in the unwarned condition. There was less SICI₃ in the warned condition than in the unwarned condition (Experiment 1) whereas SICI_1.5 was similar in both conditions (Experiment 2). There was less LICI₁₀₀ in the warned condition than in the unwarned condition (Experiment 3). The intracortical inhibitory processes measured here cannot explain the suppression of MEP amplitude in the warned condition. We propose that the suppression of MEP amplitude is the result of an inhibitory mechanism, which acts on primary motor cortex to prevent premature response during the foreperiod.     

Time course of automatic emotion regulation during a facial Go/Nogo task

Neuroimaging research has determined that the neural correlates of automatic emotion regulation (AER) include the anterior cingulate cortex. However, the corresponding time course remains unknown. In the current study, we collected event-related potentials (ERPs) from 20 healthy volunteers during a judgment of the gender of emotional faces in a cued Go/Nogo task. The results indicate that Go-N2 amplitudes and latencies following positive and negative faces decreased more than those following neutral faces; Nogo-N2 amplitudes and latencies did not vary with valence. Moreover, positive and negative faces prompted higher P3 amplitudes and shorter P3 latencies than neutral faces in both Go and Nogo trials. These observations suggest that in the executive processes, Go-N2 reflects top-down attention toward emotions, while Go-P3 reflects only motivated attention; in the inhibitory processes, Nogo-N2 reflects cognitive conflict monitoring, while Nogo-P3 overlaps with the automatic response inhibition of emotions. These observations imply that AER can modulate early ERP components, and both Go-N2 and Nogo-P3 can be used as electrophysiological indices of AER.     

Hand distance modulates the electrophysiological correlates of target selection during a tactile search task

This study investigated whether the N140cc ERP component, described as a possible electrophysiological marker of target selection in touch, was modulated by body posture. Participants performed a tactile search task in which they had to localize a tactile target, presented to the left or right hand, while a simultaneous distractor was delivered to the opposite hand. Importantly, the distance between target and distractor (hands separation) was manipulated in different experimental conditions (near vs. far hands). Results showed reduced errors and enhanced amplitudes of the late N140cc when the hands were far apart than in close proximity. This suggests that the competition between target and distractor is stronger when the hands are close together in the near condition, resulting in a degraded selection process. These findings confirm that the N140cc reflects target selection during the simultaneous presentation of competing stimuli and demonstrate for the first time that the attentional mechanisms indexed by this ERP component are based at least in part on postural representations of the body.     

Event-related activity and phase locking during a psychomotor vigilance task over the course of sleep deprivation

There is profound knowledge that sleep restriction increases tonic (event‐unrelated) electroencephalographic (EEG) activity. In the present study we focused on time‐locked activity by means of phasic (event‐related) EEG analysis during a psychomotor vigilance task (PVT) over the course of sleep deprivation. Twenty healthy subjects (10 male; mean age ± SD: 23.45 ± 1.97 years) underwent sleep deprivation for 24 h. Subjects had to rate their sleepiness hourly (Karolinska Sleepiness Scale) and to perform a PVT while EEG was recorded simultaneously. Tonic EEG changes in the δ (1–4 Hz), θ (4–8 Hz) and α (8–12 Hz) frequency range were investigated by power spectral analyses. Single‐trial (phase‐locking index, PLI) and event‐related potential (ERP) analyses (P1, N1) were used to examine event‐related changes in EEG activity. Subjective sleepiness, PVT reaction times and tonic EEG activity (delta and theta spectral power) significantly increased over the night. In contrast, event‐related EEG parameters decreased throughout sleep deprivation. Specifically, the ERP component P1 diminished in amplitude, and delta and theta PLI estimates decreased progressively over the night. It is suggested that event‐related EEG measures (such as the amplitude of the P1 and especially delta/theta phase‐locking) serve as a complimentary method to track the deterioration of attention and performance during sleep loss. As these measures actually reflect the impaired response to specific events rather than tonic changes during sleep deprivation they are a promising tool for future sleep research.     

Attentional stages of information processing during a continuous performance test: A startle modification analysis

This study of 31 college students employed the startle eye-blink modification (SEM) technique to index both early and later stages of attentional processing during a memory-load version of the Continuous Performance Test (CPT). Participants viewed a series of digits and pressed a button after the digit 7 of each 3-7 sequence. A startling noise burst was presented either 120 or 1,200 ms following three preselected prepulses: target (3), nontarget (non-3 and non-7 digits), or target plus distractor (3 and simultaneous tone distractor). Greater startle inhibition occurred 120 ms following target and target-plus-distractor prepulses compared with nontargets, indicating early selective attention. No difference was observed between SEM during target and target-plus-distractor prepulses, suggesting the distractor was effectively ignored. At 1,200 ms, the three prepulse types produced nondifferential inhibition, suggesting that modality-specific selective attention occurs in anticipation of the presentation of the next CPT prepulse. These findings indicate that SEM distinguishes between different early selective attention and later anticipatory attention subprocesses underlying the CPT.     

Alpha power and coherence primarily reflect neural activity related to stages of motor response during a continuous monitoring task

Previously, EEG theta (4-6 Hz) was related to goal conflict resolution [Moore, R.A., Gale, A., Morris, P.H., Forrester, D., 2006. Theta phase locking across the neocortex reflects cortico-hippocampal recursive communication during goal conflict resolution. Int. J. Psychophysiol. 60, 260-273] in the context of theory linked with animal hippocampal theta [Gray, J.A., McNaughton, N., 2000. The Neuropsychology of Anxiety: An Enquiry into the Functions of the Septo-Hippocampal system, 2nd ed, Oxford University Press, Oxford]. Here, the hypothesis that human EEG alpha (8-12 Hz) may also be a natural analogue to animal hippocampal theta is tested. Participants engaged in a monitoring task where the object was to press a response key immediately after presentation of 4 individual, non-repeating, single integer odd digits. These were presented amongst a continuous stream of single integer digits and Xs. EEG recorded in the earlier study were reanalysed; this time extracting alpha power and coherence from the same 34 participants. Alpha had a different profile to theta and was not primarily related to goal conflict. Low alpha (8-10 Hz) coherence consistently increased at electrodes close to primary sensorimotor cortex; particularly during response execution and response inhibition. The coherence analysis revealed that high alpha (10-12 Hz) related to response execution. Supplementary analyses demonstrated widespread high alpha coherence increase during response execution, inhibition and preparation. These data were discussed within the context of motor driven 'classic alpha' and Rolandic mu. A coherence profile which differentiated response execution and response inhibition was proposed to reflect a working memory network which was activated during response execution. Also, alpha power (8-12 Hz) reduced at several central electrodes during response execution. This reflected classic Rolandic mu response. Participants displaying a predicted low alpha power trend had the fastest response times; this was linked with traditional views of low alpha's functional significance.     

Spatial distribution of activity of the neurons of the visual cortex during stimulation with a flash of diffused light

At different stages in the development of the response to a flash of diffused light, groupings of excited neurons in field 17 of the guinea pig continue to occur within the same cortical microzones. These zones are separated from neighboring microzones by narrow inhibition zones. The ensembles of cells participating in excitation form columns tapering with depth. The grouping of excited cells noted during a silent break indicates a grouping of inhibitory neurons. Three subgroups are distinguished within the ensembles according to the average dynamics of their impulse activity; the groups are reciprocally interrelated. One of the subgroups is in the lower layers of the cortex. This subgroup is characterized by stably localized foci of maximal activity; their dynamics, apparently reflecting groupings of corticofugal neurons, are sharply distinguished from the subgroups of the middle layers. The ensembles under investigation are considered to be one of the forms of activity of the structural-morphological units in the cortex.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 69, No. 1, pp. 46–54, January, 1983.     

Excitatory and inhibitory processes in primary motor cortex during the foreperiod of a warned reaction time task are unrelated to response expectancy

Reaction time (RT) is shortened when a warning signal precedes the response signal, a finding attributed to response preparation during the foreperiod between the warning and response signals. In a previous experiment, we delivered transcranial magnetic stimulation (TMS) during the short constant foreperiod of a warned RT task and found simultaneous suppression of motor evoked potential (MEP) amplitude and reduction of short-interval intracortical inhibition (SICI) on warned trials (Sinclair and Hammond in Exp Brain Res 186:385–392, 2008). To investigate the extent to which these phenomena are associated with response preparation we measured MEP amplitude and SICI during the foreperiod of a warned RT task in which three different warning signals specified the probability (0, 0.5, or 0.83) of response signal presentation. MEP amplitude was suppressed (Experiment 1) and SICI reduced (Experiment 2) equally in all of the warned conditions relative to when TMS was delivered in the inter-trial interval (ITI) suggesting that the modulation of primary motor cortex excitability during the foreperiod does not depend on momentary response expectancy induced by the warning signal. The reduction of SICI and suppression of MEP amplitude can be explained by assuming that a warning signal induces automatic motor cortical activation which is balanced by a competing inhibition to prevent premature response. A composite measure which weighted both speed and accuracy of response was positively correlated with the MEP amplitude during both the foreperiod and the ITI, suggesting that high motor cortical excitability is associated with optimized preparatory strategies for fast and accurate response.     

Resting cardiac vagal tone predicts intraindividual reaction time variability during an attention task in a sample of young and healthy adults

Intraindividual reaction time variability (IIV), defined as the variability in trial‐to‐trial response times, is thought to serve as an index of central nervous system function. As such, greater IIV reflects both poorer executive brain function and cognitive control, in addition to lapses in attention. Resting‐state vagally mediated heart rate variability (vmHRV), a psychophysiological index of self‐regulatory abilities, has been linked with executive brain function and cognitive control such that those with greater resting‐state vmHRV often perform better on cognitive tasks. However, research has yet to investigate the direct relationship between resting vmHRV and task IIV. The present study sought to examine this relationship in a sample of 104 young and healthy participants who first completed a 5‐min resting‐baseline period during which resting‐state vmHRV was assessed. Participants then completed an attentional (target detection) task, where reaction time, accuracy, and trial‐to‐trial IIV were obtained. Results showed resting vmHRV to be significantly related to IIV, such that lower resting vmHRV predicted higher IIV on the task, even when controlling for several covariates (including mean reaction time and accuracy). Overall, our results provide further evidence for the link between resting vmHRV and cognitive control, and extend these notions to the domain of lapses in attention, as indexed by IIV. Implications and recommendations for future research on resting vmHRV and cognition are discussed.