Unconscious priming of a no-go response

Although previous findings suggest that motor preparation can be initiated unconsciously, there is some debate as to whether inhibitory control can occur unconsciously. Results from research involving response conflict points to an association between inhibitory control and conscious awareness. However, no previous research has assessed whether unconscious information can influence brain activity correlates of inhibition when a response must be completely withheld. We recorded event-related potentials (ERPs) in a go/no-go task with subliminal primes and demonstrated that inhibition-related ERP components were modulated as a function of the congruency of the primes. Furthermore, these ERP modulations were directly related to the extent to which participants' performance was influenced by the primes. These findings suggest that inhibition of an impending motor action can be initiated by an unconscious stimulus.     

Microsaccadic inhibition and P300 enhancement in a visual oddball task

It has recently been demonstrated that the presentation of visual oddballs induces a prolonged inhibition of microsaccades. The amplitude of the P300 component in event-related potentials (ERPs) has been shown to be sensitive to the category (target vs. nontarget) of the eliciting stimulus, its overall probability, and the preceding stimulus sequence. In the present study we further specify the functional underpinnings of the prolonged microsaccadic inhibition in the visual oddball task, showing that the stimulus category, the frequency of a stimulus, and the preceding stimulus sequence influence microsaccade rate. Furthermore, by co-recording ERPs and eye movements, we were able to demonstrate that, despite being largely sensitive to the same experimental manipulation, the amplitude of P300 and the microsaccadic inhibition predict each other only weakly.     

When beef primes reef more than leaf: Orthographic information affects phonological priming in spoken word recognition

This study was designed to investigate orthographic effects on spoken word recognition by combining the priming paradigm with a measure of event-related brain potentials (ERPs). Primes and targets either shared both orthography and phonology of the rhyme ( beef-reef ) or they shared rhyme phonology only ( leaf-reef ). The two "related" conditions were compared against an "unrelated" condition ( sick-reef ). The results revealed a significant orthographic priming effect that was present on the early part of the N400 and that occurred as early as the phonological priming effect itself. Importantly, phonological and orthographic priming effects had different topographic distributions: The phonological priming effect was localized over centro-posterior regions, whereas the orthographic priming effect was more anterior. These results support a theory according to which orthographic information is coactivated online in spoken word recognition.     

Proactive and reactive control in S-R compatibility: a brain potential analysis

We investigated how proactive and reactive control facilitates performance in mixed stimulus-response compatibility (SRC) tasks. SRC effects were eliminated in mixed tasks and reversed following incompatible trials. In mixed tasks, early preferential response activation was present in stimulus-locked lateralized readiness potentials (LRPs) but reduced following incompatible trials. In event-related potentials (ERPs), stimulus-locked N2 was enhanced in all mixed trials but was not significantly influenced by the preceding trial. A response-locked fronto-central negative component (N-120), peaking just before the response, was largest for mixed compatible trials preceded by incompatible trials. This N-120 was paired with an enhancement to the peak of the response-locked LRP. Proactive control is involved in selection of an S-R mapping via the indirect route of a dual-route model. Reactive control corrects the S-R mapping, particularly when alternating between S-R mappings.     

Impaired semantic processing during task‐set switching: Evidence from the N400 in rapid serial visual presentation

The cognitive system is able to reconfigure mental resources flexibly to adapt to new a task. While task‐set switching is known to be detrimental to behavioral performance, less is known about the precise loci of these effects on stimulus processing. We measured event‐related potentials to explore the neural consequences of task‐set switching on semantic processing. We examined the context‐sensitive N400 component evoked by the second of two target words embedded in a rapid serial visual presentation under conditions that involved either a task‐set switch or no switching. Whereas the N400 was unaffected by the lag separating the targets in the absence of switching, it was delayed and attenuated in the switch condition when the targets were adjacent in the sequence. These findings indicate that task‐set reconfiguration temporarily prevents semantic activation and provide evidence for the nonautomaticity of semantic processing of words.     

Pupillometry and P3 index the locus coeruleus–noradrenergic arousal function in humans

The adaptive gain theory highlights the pivotal role of the locus coeruleus–noradrenergic (LC‐NE) system in regulating task engagement. In humans, however, LC‐NE functional dynamics remain largely unknown. We evaluated the utility of two candidate psychophysiological markers of LC‐NE activity: the P3 event‐related potential and pupil diameter. Electroencephalogram and pupillometry data were collected from 24 participants who performed a 37‐min auditory oddball task. As predicted by the adaptive gain theory, prestimulus pupil diameter exhibited an inverted U‐shaped relationship to P3 and task performance such that largest P3 amplitudes and optimal performance occurred at the same intermediate level of pupil diameter. Large phasic pupil dilations, by contrast, were elicited during periods of poor performance and were followed by reengagement in the task and increased P3 amplitudes. These results support recent proposals that pupil diameter and the P3 are sensitive to LC‐NE mode.     

Cognitive control in the intertrial interval: Evidence from EEG alpha power

This study used electroencephalogram (EEG) power spectrum analyses to characterize neural activity during the intertrial interval, a period during which online cognitive adjustments in response to errors or conflict are thought to occur. EEG alpha power was quantified as an inverse index of cerebral activity during the period between each response and the next stimulus in a Stroop task. Alpha power was significantly reduced following error responses compared to correct responses, indicating greater cerebral activity following errors. Reduced alpha power was also observed following Stroop conflict trials compared to no‐conflict trials, suggesting that conflict engages processes of mental adjustment. Finally, hemispheric differences in alpha power during the intertrial interval supported the complementary roles of the left and right hemispheres in behavioral activation and inhibition.     

Brief Reports: The role of temporal predictability in the anticipatory biasing of sensory cortex during visuospatial shifts of attention

The presentation of an attention‐directing cue elicits a lateralized ERP deflection called the late directing attention positivity (LDAP) and lateralized changes in alpha‐band elelctroencephalogram oscillations. Both of these electrophysiological responses have been independently linked to biasing of visual cortex in anticipation of an impending target. However, the LDAP is not always observed, and the link between the ERP and alpha‐band modulations remains unclear. Here, we examined the effect of advance knowledge of the time of target onset on the ERP and alpha‐band responses to cues. The LDAP was present only when the attention‐directing cues accurately indicated the time of target appearance, whereas two sequential attention‐related alpha‐band modulations were observed regardless of the temporal information provided by the cues. Thus, alpha‐band activity may be a more reliable index of pretarget biasing of visual cortical activity than lateralized ERP effects.     

What is and what could have been: An ERP study on counterfactual comparisons

Prior research indicates that the feedback‐related negativity (FRN) reflects a good versus bad evaluation of decision outcomes, which is insensitive to the local utilitarian relation between chosen and unchosen outcomes. We tested whether this negative finding holds when the chosen outcome has an objective value of zero and therefore a comparison with the unchosen outcome is needed to identify overall choice valence. Participants completed a gambling task in which chosen and unchosen options could result in monetary wins, losses, or breaking even. Results show that the FRN does not reflect local favorableness but rather a dichotomy of gain versus no‐gain for both chosen and unchosen outcomes. In contrast, P300 amplitude appears to reflect motivational salience derived from counterfactual comparisons of chosen and unchosen outcomes. Based on our and prior findings, we propose a threefold taxonomy of contextual factors and their relation to the FRN.     

The stability of error-related brain activity with increasing trials

The error-related negativity (ERN) and error positivity (Pe) are increasingly being examined as neural correlates of response monitoring. The minimum number of error trials included in grand averages varies across studies; indeed, there has not been a systematic investigation on the number of trials required to obtain a stable ERN and Pe. In the current study, the ERN and Pe were quantified as two random trials were added to participants' ( N =53) ERP averages. Adding trials increased the correlation with the grand average ERN and Pe; however, high correlations ( r s>.80) were obtained with only 6 trials. Internal reliability of the ERN and Pe reached moderate levels after 6 and 2 trials and the signal-to-noise ratio of the ERN and Pe did not change after 8 and 4 trials, respectively. Combined, these data suggest that the ERN and Pe can be quantified using a minimum of between 6 and 8 error trials.     

Selective suppression of self-initiated sounds in an auditory stream: An ERP study

Numerous studies have shown that the N1 event-related potential (ERP) response is attenuated when it is elicited by self-initiated sounds. This N1 suppression effect is generally interpreted to reflect an internal prediction mechanism, which enables the discrimination of the sensory consequences of our own actions and those of others. The blocked design used in the forerunner studies (i.e., self- and externally initiated sounds presented in different blocks) seriously limits the relevance of these findings, because the N1 effect can simply be explained by contextual task differences. In the present study, self- and externally initiated sounds were mixed within blocks. N1 suppression was found, and its magnitude was even larger than that observed in a traditional blocked condition. This result supports the involvement of an internal prediction mechanism in the discrimination of the sensory consequences of one's own actions and those of others.     

The N1 effect of temporal attention is independent of sound location and intensity: Implications for possible mechanisms of temporal attention

It has been repeatedly shown that the auditory N1 is enhanced for sounds presented at an attended time point. The present study investigated the underlying mechanisms using a temporal cuing paradigm. In each trial, an auditory cue indicated at which time point a second sound could be relevant for response selection. Crucially, in addition to temporal attention, two physical sound features with known effects on the sensory N1 were manipulated: location and intensity. Positive evidence for conjoint effects of attention and location or attention and intensity would corroborate the notion that the sensory N1 was modulated by temporal attention, thus supporting a gain mechanism. However, the N1 effect of temporal attention was not similarly lateralized as the sensory N1, and, moreover, it was independent of sound intensity. Thus, the present results do not provide compelling evidence that temporal attention involves an increase in sensory gain.     

Contextual task difficulty modulates stimulus discrimination: Electrophysiological evidence for interaction between sensory and executive processes

The occipital‐temporal N1 component of the event‐related potential (ERP) has previously been shown to index a stimulus discrimination process. However, the N1 has not consistently been shown to be sensitive to the difficulty of stimulus discrimination. Here, we manipulated the difficulty of stimulus discrimination by modulating the similarity between serially presented targets and nontargets. The same target stimulus was employed in both easy and difficult discrimination contexts, and these physically identical target stimuli elicited a larger N1 and smaller P3b in the difficult task context. Moreover, when targets were incorrectly categorized, N1 amplitude was diminished and a P3b was not elicited. These findings provide evidence that the N1 component reflects a sensory discrimination process that is modulated by executive control, and that this component can index discrimination errors when stimulus discrimination is difficult.     

Effects of premature lure stimuli on 2nd‐target identification in rapid serial visual presentation: Inhibition induced by lures or by 1st target?

In many rapid serial presentation tasks, two targets ("T1" and "T2") have to be distinguished from background stimuli. Here, digits ("lures") were interspersed among the background letters, differing from the T2 digit by occurring before rather than after T1. The resulting inhibitory effects on T2 identification may either be evoked directly by the lures or be triggered by T1, interfering with positive priming of lures on T2. To distinguish between these two alternatives, lures, T1, and T2 were presented in two different simultaneously running streams, T2 was or was not the same digit as a lure, and EEG potentials related to lures, T1, and T2 were recorded. Effects on T2 identification better fit the view that lures exerted positive priming interrupted by T1. Recurrence of lures in the trial led to abridged duration of the lure-evoked N2pc, and T2-evoked N2pc was reduced after lures. Also these N2pc effects may reflect positive priming.     

Masked targets trigger event‐related potentials indexing shifts of attention but not error detection

To carry out tasks with the highest possible efficiency we have developed executive mechanisms that monitor task performance and optimize cognitive processing. It has been hypothesized that these executive mechanisms operate even without conscious awareness to maximize their sensitivity to task‐relevant outcomes. To test this hypothesis the present study examined the error‐related negativity (ERN), an electrophysiological index of the performance‐monitoring neural circuitry, during masked visual search. The findings show that representations of target objects that are processed perceptually, but not to the level of awareness, fail to elicit an ERN despite the ability of these targets to elicit a shift of attention. These findings indicate that the performance‐monitoring mechanism indexed by the ERN requires target information to be processed to the level of awareness for a mismatch between stimulus and response to be detected.     

The spotlight of attention illuminates failed feature-based expectancies

A well-replicated finding is that visual stimuli presented at an attended location are afforded a processing benefit in the form of speeded reaction times and increased accuracy (Mangun, ; Posner,). This effect has been described using a spotlight metaphor, in which all stimuli within the focus of spatial attention receive facilitated processing, irrespective of other stimulus parameters. However, the spotlight metaphor has been brought into question by a series of combined expectancy studies that demonstrated that the behavioral benefits of spatial attention are contingent on secondary feature-based expectancies (Kingstone,). The present work used an event-related potential (ERP) approach to reveal that the early neural signature of the spotlight of spatial attention is not sensitive to the validity of secondary feature-based expectancies.     

Attenuation of auditory ERPs to action‐sound coincidences is not explained by voluntary allocation of attention

The event‐related potential (ERP) correlates of sound detection are attenuated when eliciting sounds coincide with our own actions. The role of attention in this effect was investigated in two experiments by presenting tones separated by random intervals. In the homogeneous condition of Experiments 1 and 2, the same tone was repeated, whereas in the mixed condition of Experiment 1, tones with five different frequencies were presented. Participants performed a time‐interval production task by marking intervals with keypresses in Experiment 1, and tried to produce keypress‐tone coincidences in Experiment 2. Although the auditory ERPs were attenuated for coincidences, no modulation by the multiplicity of tone frequencies in Experiment 1, or by the task‐relevancy of tones and coincidences in Experiment 2, was found. This suggests that coincidence‐related ERP attenuation cannot be fully explained by voluntary attentional mechanisms.     

Electrophysiological responses to visuospatial regularity

Humans are quicker to detect reflectional than rotational or translational symmetry, despite the fact that these patterns are equally regular. We were interested in the neural correlates of these perceptual effects. Participants viewed random, reflection, rotation, and translation patterns while we recorded EEG from the scalp. Half the participants classified the pattern regularity overtly, the other half did not explicitly attend to pattern regularity but reported rare oddball trials, where two squares were embedded among the dots. The amplitude of a symmetry‐related ERP known as the sustained posterior negativity was most pronounced for reflection, then rotation and translation. We suggest that reflectional symmetry, despite its biological significance, may not be processed by unique visual mechanisms, but instead it could be a preferred stimulus for a more general regularity‐sensitive network in the extrastriate visual cortex.     

The component structure of ERP subsequent memory effects in the Von Restorff paradigm and the word frequency effect in recall

We examined the degree to which ERP components elicited by items that are isolated from their context, either by their font size (“size isolates”) or by their frequency of usage, are correlated with subsequent immediate recall. Study lists contained (a) 15 words including a size isolate, (b) 14 high frequency (HF) words with one low frequency word (“LF isolate”), or (c) 14 LF words with one HF word. We used spatiotemporal PCA to quantify ERP components. We replicated previously reported P300 subsequent memory effects for size isolates and found additional correlations with recall in the novelty P3, a right lateralized positivity, and a left lateralized slow wave that was distinct from the slow wave correlated with recall for nonisolates. LF isolates also showed evidence of a P300 subsequent memory effect and also elicited the left lateralized subsequent memory effect, supporting a role of distinctiveness in word frequency effects in recall.     

Is ocular voltage propagation to the electroencephalogram frequency dependent?

Conventional eye correction methods subtract portions (propagation coefficients; Bs ) of electrooculogram (EOG) voltages from the electroencephalogram (EEG). The frequency domain approach (FDA) uses different B s for different frequencies whereas the time domain approach (TDA) uses the same B s. To determine whether measured B s are dependent on frequency and whether one should employ frequency-dependent methods, 20 min of EEG from eye movement (EM) and blink data (24 participants) were recorded, and B s were calculated for eye movement ERPs of differing signal-to-noise ratios for frequency bands ranging from 0 to 40 Hz and compared. At high signal to noise, EM B s for different frequency bands did not differ, for both vertical and horizontal EOG, at all scalp sites tested. There were small differences in blink B s for different bands, but smaller than the margin of error of this analysis. This indicates that TDA may be more appropriate than FDA.