Tactile cues are more intrinsically linked to motor timing than visual cues in visual-tactile sensorimotor synchronization.

Many tasks require precise synchronization with external sensory stimuli, such as driving a car. This study investigates whether combined visual-tactile information provides additional benefits to movement synchrony over separate visual and tactile stimuli and explores the relationship with the temporal binding window for multisensory integration. In Experiment 1, participants completed a sensorimotor synchronization task to examine movement variability and a simultaneity judgment task to measure the temporal binding window. Results showed similar synchronization variability between visual-tactile and tactile-only stimuli, but significantly lower than visual only. In Experiment 2, participants completed a visual-tactile sensorimotor synchronization task with cross-modal stimuli presented inside (stimulus onset asynchrony 80 ms) and outside (stimulus-onset asynchrony 400 ms) the temporal binding window to examine temporal accuracy of movement execution. Participants synchronized their movement with the first stimulus in the cross-modal pair, either the visual or tactile stimulus. Results showed significantly greater temporal accuracy when only one stimulus was presented inside the window and the second stimulus was outside the window than when both stimuli were presented inside the window, with movement execution being more accurate when attending to the tactile stimulus. Overall, these findings indicate there may be a modality-specific benefit to sensorimotor synchronization performance, such that tactile cues are weighted more strongly than visual information as tactile information is more intrinsically linked to motor timing than visual information. Further, our findings indicate that the visual-tactile temporal binding window is related to the temporal accuracy of movement execution.

N1-P2 event-related potentials and perceived intensity are associated: The effects of a weak pre-stimulus and attentional load on processing of a subsequent intense stimulus.

A weak stimulus presented immediately before a more intense one reduces both the N1-P2 cortical response and the perceived intensity of the intense stimulus. The former effect is referred to as cortical prepulse inhibition (PPI), the latter as prepulse inhibition of perceived stimulus intensity (PPIPSI). Both phenomena are used to study sensory gating in clinical and non-clinical populations, however little is known about their relationship. Here, we investigated 1) the possibility that cortical PPI and PPIPSI are associated, and 2) how they are affected by attentional load. Participants were tasked with comparing the intensity of an electric pulse presented alone versus one preceded 200 ms by a weaker electric prepulse (Experiment 1), or an acoustic pulse presented alone with one preceded 170 ms by a weaker acoustic prepulse (Experiment 2). A counting task (easy vs. hard) manipulating attentional load was included in Experiment 2. In both experiments, we observed a relationship between N1-P2 amplitude and perceived intensity, where greater cortical PPI was associated with a higher probability of perceiving the 'pulse with prepulse' as less intense. Moreover, higher attentional load decreased observations of PPIPSI but had no effect on N1-P2 amplitude. Based on the findings we propose that PPIPSI partially relies on the allocation of attentional resources towards monitoring cortical channels that process stimulus intensity characteristics such as the N1-P2 complex.

Investigating the Role of Leading Sensory Modality and Autistic Traits in the Visual-Tactile Temporal Binding Window.

Our ability to integrate multisensory information depends on processes occurring during the temporal binding window. There is limited research investigating the temporal binding window for visual-tactile integration and its relationship with autistic traits, sensory sensitivity, and unusual sensory experiences. We measured the temporal binding window for visual-tactile integration in 27 neurotypical participants who completed a simultaneity judgement task and three questionnaires: the Autism Quotient, the Glasgow Sensory Questionnaire, and the Multi-Modality Unusual Sensory Experiences Questionnaire. The average width of the visual-leading visual-tactile (VT) temporal binding window was 123 ms, significantly narrower than the tactile-leading visual-tactile (TV) window (193 ms). When comparing crossmodal (visual-tactile) stimuli with unimodal (visual-visual or tactile-tactile), the temporal binding window was significantly larger for crossmodal stimuli (VT: 123 ms; TV: 193 ms) than for unimodal pairs of stimuli (visual: 38 ms; tactile 42 ms). We did not find evidence to support a relationship between the size of the temporal binding window and autistic traits, sensory sensitivities, or unusual sensory perceptual experiences in this neurotypical population. Our results indicate that the leading sense presented in a multisensory pair influences the width of the temporal binding window. When tactile stimuli precede visual stimuli it may be difficult to determine the temporal boundaries of the stimuli, which leads to a delay in shifting attention from tactile to visual stimuli. This ambiguity in determining temporal boundaries of stimuli likely influences our ability to decide on whether stimuli are simultaneous or nonsimultaneous, which in turn leads to wider temporal binding windows.

The effects of left prefrontal stimulation on selective attention and emotional reactivity for positive and negative information.

Transcranial direct current stimulation targeting lateral prefrontal areas may attenuate attentional vigilance for negative content and reduce emotional reactivity. However, little research to date has examined how such stimulation may affect attention towards and emotional reactivity to positive emotional content. The aim of this study was to examine whether anodal tDCS targeting the left dorsolateral prefrontal cortex would affect attentional bias towards either or both negative and positive content, and similarly, how it would impact emotional reactivity to negative and positive emotional content among healthy individuals. Unselected participants (N = 101) were recruited (Mage = 22.57, SD = 5.60; 66.33% female) and allocated to either an active or sham tDCS condition. Attentional bias was measured using an eye-tracking task involving negative-neutral and positive-neutral image pairs, followed by an emotional reactivity assessment task involving negative and positive video content (self-report and heart rate variability). Results showed no evidence that tDCS influenced attentional patterns towards either positive or negative information, nor was there evidence that tDCS influenced self-reported anxious mood or physiological arousal. However, participants in the active tDCS condition reported higher positive mood in response to both the positive and negative videos compared to those in the sham condition and also higher arousal in response to positive content and lower arousal in response to negative content, with those in the sham tDCS condition showing the reverse pattern of effects. As such, tDCS effects on emotional reactivity to positive and negative content were restricted to self-report measures.

Pupil dilation during encoding, but not type of auditory stimulation, predicts recognition success in face memory.

We encounter and process information from multiple sensory modalities in our daily lives, and research suggests that learning can be more efficient when contexts are multisensory. In this study, we were interested in whether face identity recognition memory might be improved in multisensory learning conditions, and to explore associated changes in pupil dilation during encoding and recognition. In two studies participants completed old/new face recognition tasks wherein visual face stimuli were presented in the context of sounds. Faces were learnt alongside no sound, low arousal sounds (Experiment 1), high arousal non-face relevant, or high arousal face relevant (Experiment 2) sounds. We predicted that the presence of sounds during encoding would improve later recognition accuracy, however, the results did not support this with no effect of sound condition on memory. Pupil dilation, however, was found to predict later successful recognition both at encoding and during recognition. While these results do not provide support to the notion that face learning is improved under multisensory conditions relative to unisensory conditions, they do suggest that pupillometry may be a useful tool to further explore face identity learning and recognition.

Event-Related Potentials of Single-Sided Deaf Cochlear Implant Users: Using a Semantic Oddball Paradigm in Noise.

INTRODUCTION: In individuals with single-sided deafness (SSD), who are characterised by profound hearing loss in one ear and normal hearing in the contralateral ear, binaural input is no longer present. A cochlear implant (CI) can restore functional hearing in the profoundly deaf ear, with previous literature demonstrating improvements in speech-in-noise intelligibility with the CI. However, we currently have limited understanding of the neural processes involved (e.g., how the brain integrates the electrical signal produced by the CI with the acoustic signal produced by the normal hearing ear) and how modulation of these processes with a CI contributes to improved speech-in-noise intelligibility. Using a semantic oddball paradigm presented in the presence of background noise, this study aims to investigate how the provision of CI impacts speech-in-noise perception of SSD-CI users. METHOD: Task performance (reaction time, reaction time variability, target accuracy, subjective listening effort) and high density electroencephalography from twelve SSD-CI participants were recorded, while they completed a semantic acoustic oddball task. Reaction time was defined as the time taken for a participant to press the response button after stimulus onset. All participants completed the oddball task in three different free-field conditions with the speech and noise coming from different speakers. The three tasks were: (1) CI-On in background noise, (2) CI-Off in background noise, and (3) CI-On without background noise (Control). Task performance and electroencephalography data (N2N4 and P3b) were recorded for each condition. Speech in noise and sound localisation ability were also measured. RESULTS: Reaction time was significantly different between all tasks with CI-On (M [SE] = 809 [39.9] ms) having faster RTs than CI-Off (M [SE] = 845 [39.9] ms) and Control (M [SE] = 785 [39.9] ms) being the fastest condition. The Control condition exhibited significantly shorter N2N4 and P3b area latency compared to the other two conditions. However, despite these differences noticed in RTs and area latency, we observed similar results between all three conditions for N2N4 and P3b difference area. CONCLUSION: The inconsistency between the behavioural and neural results suggests that EEG may not be a reliable measure of cognitive effort. This rationale is further supported by different explanations used in past studies to explain N2N4 and P3b effects. Future studies should look to alternative measures of auditory processing (e.g., pupillometry) to gain a deeper understanding of the underlying auditory processes that facilitate speech-in-noise intelligibility.

Evolving changes in cortical and subcortical excitability during movement preparation: A study of brain potentials and eye-blink reflexes during loud acoustic stimulation.

During preparation for action, the presentation of loud acoustic stimuli (LAS) can trigger movements at very short latencies in a phenomenon called the StartReact effect. It was initially proposed that a special, separate subcortical mechanism that bypasses slower cortical areas could be involved. We sought to examine the evidence for a separate mechanism against the alternative that responses to LAS can be explained by a combination of stimulus intensity effects and preparatory states. To investigate whether cortically mediated preparatory processes are involved in mediating reactions to LAS, we used an auditory reaction task where we manipulated the preparation level within each trial by altering the conditional probability of the imperative stimulus. We contrasted responses to non-intense tones and LAS and examined whether cortical activation and subcortical excitability and motor responses were influenced by preparation levels. Increases in preparation levels were marked by gradual reductions in reaction time (RT) coupled with increases in cortical activation and subcortical excitability - at both condition and trial levels. Interestingly, changes in cortical activation influenced motor and auditory but not visual areas - highlighting the widespread yet selective nature of preparation. RTs were shorter to LAS than tones, but the overall pattern of preparation level effects was the same for both stimuli. Collectively, the results demonstrate that LAS responses are indeed shaped by cortically mediated preparatory processes. The concurrent changes observed in brain and behavior with increasing preparation reinforce the notion that preparation is marked by evolving brain states which shape the motor system for action.

A Study of Event-Related Potentials During Monaural and Bilateral Hearing in Single-Sided Deaf Cochlear Implant Users.

OBJECTIVES: Single-sided deafness (SSD) is characterized by a profoundly deaf ear and normal hearing in the contralateral ear. A cochlear implant (CI) is the only method to restore functional hearing in a profoundly deaf ear. In a previous study, we identified that the cortical processing of a CI signal differs from the normal-hearing ear (NHE) when directly compared using an auditory oddball paradigm consisting of pure tones. However, exactly how the brain integrates the electrical and acoustic signal is not well investigated. This study aims to understand how the provision of the CI in combination with the NHE may improve SSD CI users' ability to discriminate and evaluate auditory stimuli. DESIGN: Electroencephalography from 10 SSD-CI participants (4 participated in the previous pure-tone study) were recorded during a semantic acoustic oddball task, where they were required to discriminate between odd and even numbers. Stimuli were presented in four hearing conditions: directly through the CI, directly to the NHE, or in free field with the CI switched on and off. We examined task-performance (response time and accuracy) and measured N1, P2, N2N4, and P3b event-related brain potentials (ERPs) linked to the detection, discrimination, and evaluation of task relevant stimuli. Sound localization and speech in noise comprehension was also examined. RESULTS: In direct presentation, task performance was superior during NHE compared with CI (shorter and less varied reaction times [~720 versus ~842 msec], higher target accuracy [~93 versus ~70%]) and early neural responses (N1 and P2) were enhanced for NHE suggesting greater signal saliency. However, the size of N2N4 and P3b target-standard effects did not differ significantly between NHE and CI. In free field, target accuracy was similarly high with the CI (FF-On) and without the CI (FF-Off) (~95%), with some evidence of CI interference during FF-On (more variable and slightly but significantly delayed reaction times [~737 versus ~709 msec]). Early neural responses and late effects were also greater during FF-On. Performance on sound localization and speech in noise comprehension (S CI N NHE configuration only) was significantly greater during FF-On. CONCLUSIONS: Both behavioral and neural responses in the semantic oddball task were sensitive to CI in both direct and free-field presentations. Direct conditions revealed that participants could perform the task with the CI alone, although performance was suboptimal and early neural responses were reduced when compared with the NHE. For free-field, the addition of the CI was associated with enhanced early and late neural responses, but this did not result in improved task performance. Enhanced neural responses show that the additional input from the CI is modulating relevant perceptual and cognitive processes, but the benefit of binaural hearing on behavior may not be realized in simple oddball tasks which can be adequately performed with the NHE. Future studies interested in binaural hearing should examine performance under noisy conditions and/or use spatial cues to allow headroom for the measurement of binaural benefit.

Anodal-TDCS over Left-DLPFC Modulates Motor Cortex Excitability in Chronic Lower Back Pain.

Chronic pain is associated with abnormal cortical excitability and increased pain intensity. Research investigating the potential for transcranial direct current stimulation (tDCS) to modulate motor cortex excitability and reduce pain in individuals with chronic lower back pain (CLBP) yield mixed results. The present randomised, placebo-controlled study examined the impact of anodal-tDCS over left-dorsolateral prefrontal cortex (left-DLPFC) on motor cortex excitability and pain in those with CLBP. Nineteen participants with CLBP (Mage = 53.16 years, SDage = 14.80 years) received 20-min of sham or anodal tDCS, twice weekly, for 4 weeks. Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed using paired-pulse Transcranial Magnetic Stimulation prior to and immediately following the tDCS intervention. Linear Mixed Models revealed no significant effect of tDCS group or time, on SICI or ICF. The interactions between tDCS group and time on SICI and ICF only approached significance. Bayesian analyses revealed the anodal-tDCS group demonstrated higher ICF and SICI following the intervention compared to the sham-tDCS group. The anodal-tDCS group also demonstrated a reduction in pain intensity and self-reported disability compared to the sham-tDCS group. These findings provide preliminary support for anodal-tDCS over left-DLPFC to modulate cortical excitability and reduce pain in CLBP.

The effect of prepulse amplitude and timing on the perception of an electrotactile pulse.

The perceived intensity of an intense stimulus as well as the startle reflex it elicits can both be reduced when preceded by a weak stimulus (prepulse). Both phenomena are used to characterise the processes of sensory gating in clinical and non-clinical populations. The latter phenomenon, startle prepulse inhibition (PPI), is conceptualised as a measure of pre-attentive sensorimotor gating due to its observation at short latencies. In contrast, the former, prepulse inhibition of perceived stimulus intensity (PPIPSI), is believed to involve higher-order cognitive processes (e.g., attention), which require longer latencies. Although conceptually distinct, PPIPSI is often studied using parameters that elicit maximal PPI, likely limiting what we can learn about sensory gating's influence on conscious perception. Here, we tested an array of stimulus onset asynchronies (SOAs; 0-602 ms) and prepulse intensities (0-3× perceptual threshold) to determine the time course and sensitivity to the intensity of electrotactile PPIPSI. Participants were required to compare an 'unpleasant but not painful' electric pulse to their left wrist that was presented alone with the same stimulus preceded by an electric prepulse, and report which pulse stimulus felt more intense. Using a 2× perceptual threshold prepulse, PPIPSI emerged as significant at SOAs from 162 to 602 ms. We conclude that evidence of electrotactile PPIPSI at SOAs of 162 ms or longer is consistent with gating of perception requiring higher-level processes, not measured by startle PPI. The possible role of attentional processes, stimuli intensity, modality-specific differences, and methods of investigating PPIPSI further are discussed.

Odd-even oddball task: Evaluating event-related potentials during word discrimination compared to speech-token and tone discrimination.

Tonal and speech token auditory oddball tasks have been commonly used to assess auditory processing in various populations; however, tasks using non-word sounds may fail to capture the higher-level ability to interpret and discriminate stimuli based on meaning, which are critical to language comprehension. As such, this study examines how neural signals associated with discrimination and evaluation-processes (P3b) from semantic stimuli compare with those elicited by tones and speech tokens. This study comprises of two experiments, both containing thirteen adults with normal hearing in both ears (PTA ≤ 20 dB HL). Scalp electroencephalography and auditory event related potentials were recorded in free field while they completed three different oddball tasks: (1) tones, (2) speech tokens and (3) odd/even numbers. Based on the findings of experiment one, experiment two was conducted to understand if the difference in responses from the three tasks was attributable to stimulus duration or other factors. Therefore, in experiment one, stimulus duration was not controlled and in experiment two, the duration of each stimulus was modified to be the same across all three tasks (∼400 ms). In both experiments, P3b peak latency was significantly different between all three tasks. P3b amplitude was sensitive to reaction time, with tasks that had a large reaction time variability resulting in the P3b amplitude to be smeared, thereby reducing the amplitude size. The findings from this study highlight the need to consider all factors of the task before attributing any effects to any additional process, such as semantic processing and mental effort. Furthermore, it highlights the need for more cautious interpretation of P3b results in auditory oddball tasks.

Offline Parietal Intermittent Theta Burst Stimulation or Alpha Frequency Transcranial Alternating Current Stimulation Has No Effect on Visuospatial or Temporal Attention.

Non-invasive brain stimulation is a growing field with potentially wide-ranging clinical and basic science applications due to its ability to transiently and safely change brain excitability. In this study we include two types of stimulation: repetitive transcranial magnetic stimulation (rTMS) and transcranial alternating current stimulation (tACS). Single session stimulations with either technique have previously been reported to induce changes in attention. To better understand and compare the effectiveness of each technique and the basis of their effects on cognition we assessed changes to both temporal and visuospatial attention using an attentional blink task and a line bisection task following offline stimulation with an intermittent theta burst (iTBS) rTMS protocol or 10 Hz tACS. Additionally, we included a novel rTMS stimulation technique, low-intensity (LI-)rTMS, also using an iTBS protocol, which uses stimulation intensities an order of magnitude below conventional rTMS. Animal models show that low-intensity rTMS modulates cortical excitability despite sub-action potential threshold stimulation. Stimulation was delivered in healthy participants over the right posterior parietal cortex (rPPC) using a within-subjects design (n = 24). Analyses showed no evidence for an effect of any stimulation technique on spatial biases in the line bisection task or on magnitude of the attentional blink. Our results suggests that rTMS and LI-rTMS using iTBS protocol and 10 Hz tACS over rPPC do not modulate performance in tasks assessing visuospatial or temporal attention.

Engagement of the contralateral limb can enhance the facilitation of motor output by loud acoustic stimuli.

When intense sound is presented during light muscle contraction, inhibition of the corticomotoneuronal pathway is observed. During action preparation, this effect is reversed, with sound resulting in excitation of the corticomotoneuronal pathway. We investigated how the combined maintenance of a muscle contraction during preparation for a ballistic action impacts the magnitude of the facilitation of motor output by a loud acoustic stimulus (LAS), a phenomenon known as the StartReact effect. Participants executed ballistic wrist flexion movements and a LAS was presented simultaneously with the imperative signal in a subset of trials. We examined whether the force level or muscle used to maintain a contraction during preparation for the ballistic response impacted reaction time and/or the force of movements triggered by the LAS. These contractions were sustained either ipsilaterally or contralaterally to the ballistic response. The magnitude of facilitation by the LAS was greatest when low-force flexion contractions were maintained in the limb contralateral to the ballistic response during preparation. There was little change in facilitation when contractions recruited the contralateral extensor muscle or when they were sustained in the same limb that executed the ballistic response. We conclude that a larger network of neurons that may be engaged by a contralateral sustained contraction prior to initiation may be recruited by the LAS, further contributing to the motor output of the response. These findings may be particularly applicable in stroke rehabilitation, where engagement of the contralesional side may increase the benefits of a LAS to the functional recovery of movement.NEW & NOTEWORTHY The facilitation of reaction time, force, and vigor of a ballistic action by loud acoustic stimuli can be enhanced by the maintenance of a sustained contraction during preparation. This enhanced facilitation is observed when the sustained contraction is maintained with low force contralaterally and congruently with the ballistic response. This increased facilitation may be particularly applicable to rehabilitative applications of loud acoustic stimuli in improving the functional recovery of movement after neurological conditions such as stroke.

Premovement inhibition can protect motor actions from interference by response-irrelevant sensory stimulation.

KEY POINTS: Suppression of corticospinal excitability is reliably observed during preparation for a range of motor actions, leading to the belief that this preparatory inhibition is a physiologically obligatory component of motor preparation. The neurophysiological function of this suppression is uncertain. We restricted the time available for participants to engage in preparation and found no evidence for preparatory inhibition. The function of preparatory inhibition can be inferred from our findings that sensory stimulation can disrupt motor output in the absence of preparatory inhibition, but enhance motor output when inhibition is present. These findings suggest preparatory inhibition may be a strategic process which acts to protect prepared actions from external interference. Our findings have significant theoretical implications for preparatory processes. Findings may also have a pragmatic benefit in that acoustic stimulation could be used therapeutically to facilitate movement, but only if the action can be prepared well in advance. ABSTRACT: Shortly before movement initiation, the corticospinal system undergoes a transient suppression. This phenomenon has been observed across a range of motor tasks, suggesting that it may be an obligatory component of movement preparation. We probed whether this was also the case when the urgency to perform a motor action was high, in a situation where little time was available to engage in preparatory processes. We controlled the urgency of an impending motor action by increasing or decreasing the foreperiod duration in an anticipatory timing task. Transcranial magnetic stimulation (TMS; experiment 1) or a loud acoustic stimulus (LAS; experiment 2) were used to examine how corticospinal and subcortical excitability were modulated during motor preparation. Preparatory inhibition of the corticospinal tract was absent when movement urgency was high, though motor actions were initiated on time. In contrast, subcortical circuits were progressively inhibited as the time to prepare increased. Interestingly, movement force and vigour were reduced by both TMS and the LAS when movement urgency was high, and enhanced when movement urgency was low. These findings indicate that preparatory inhibition may not be an obligatory component of motor preparation. The behavioural effects we observed in the absence of preparatory inhibition were induced by both TMS and the LAS, suggesting that accessory sensory stimulation may disrupt motor output when such stimulation is presented in the absence of preparatory inhibition. We conclude that preparatory inhibition may be an adaptive strategy which can serve to protect the prepared motor action from external interference.

Acoustic stimulation increases implicit adaptation in sensorimotor adaptation.

Sensorimotor adaptation is an important part of our ability to perform novel motor tasks (i.e., learning of motor skills). Efforts to improve adaptation in healthy and clinical patients using non-invasive brain stimulation methods have been hindered by inter-individual and intra-individual variability in brain susceptibility to stimulation. Here, we explore unpredictable loud acoustic stimulation as an alternative method of modulating brain excitability to improve sensorimotor adaptation. In two experiments, participants moved a cursor towards targets, and adapted to a 30º rotation of cursor feedback, either with or without unpredictable acoustic stimulation. Acoustic stimulation improved initial adaptation to sensory prediction errors in Study 1, and improved overnight retention of adaptation in Study 2. Unpredictable loud acoustic stimulation might thus be a potent method of modulating sensorimotor adaptation in healthy adults.

Cochlear implants in single-sided deaf recipients: Near normal higher-order processing.

OBJECTIVE: Single-sided deafness (SSD) is a condition where an individual has a severe to profound sensorineural hearing loss in one ear and normal hearing on the contralateral side. The use of cochlear implants in individuals with SSD leads to functional improvements in hearing. However, it is relatively unclear how sounds incoming via the cochlear implant (independent of the hearing ear) are processed and interpreted by higher-order processes in the brain. METHODS: Scalp electroencephalography and auditory event-related potentials were recorded monaurally from nine experienced single sided cochlear implant users. Speech-in-noise and localisation tests were used to measure functional changes in hearing. RESULTS: cochlear implant use was associated with improvement in speech-in-noise and localisation tests (compared to cochlear implant off). Significant N2 and P3b effects were observed in both cochlear implant and normal hearing ear conditions, with similar waveform morphology and scalp distribution across conditions. Delayed response times and a reduced N2 (but not P3b) effect was measured in the CI condition. CONCLUSION: The brain is capable of using processes similar to those in normal hearing to discriminate sounds presented to the cochlear implant. There was evidence of processing difficulty in the cochlear implant condition which could be due to the relatively degraded signals produced by the cochlear implant compared to the normal hearing ear. SIGNIFICANCE: Understanding how the brain processes sound provided by a cochlear implant highlights how cortical responses can be used to guide implantation candidacy guidelines and influence rehabilitation recommendations.

Cumulative distribution functions: An alternative approach to examine the triggering of prepared motor actions in the StartReact effect.

There has been much debate concerning whether startling sensory stimuli can activate a fast-neural pathway for movement triggering (StartReact) which is different from that of voluntary movements. Activity in sternocleidomastoid (SCM) electromyogram is suggested to indicate activation of this pathway. We evaluated whether SCM activity can accurately identify trials which may differ in their neurophysiological triggering and assessed the use of cumulative distribution functions (CDFs) of reaction time (RT) data to identify trials with the shortest RTs for analysis. Using recent data sets from the StartReact literature, we examined the relationship between RT and SCM activity. We categorised data into short/longer RT bins using CDFs and used linear mixed-effects models to compare potential conclusions that can be drawn when categorising data on the basis of RT versus on the basis of SCM activity. The capacity of SCM to predict RT is task-specific, making it an unreliable indicator of distinct neurophysiological mechanisms. Classification of trials using CDFs is capable of capturing potential task- or muscle-related differences in triggering whilst avoiding the pitfalls of the traditional SCM activity-based classification method. We conclude that SCM activity is not always evident on trials that show the early triggering of movements seen in the StartReact phenomenon. We further propose that a more comprehensive analysis of data may be achieved through the inclusion of CDF analyses. These findings have implications for future research investigating movement triggering as well as for potential therapeutic applications of StartReact.

Preparatory suppression and facilitation of voluntary and involuntary responses to loud acoustic stimuli in an anticipatory timing task.

In this study, we sought to characterize the effects of intense sensory stimulation on voluntary and involuntary behaviors at different stages of preparation for an anticipated action. We presented unexpected loud acoustic stimuli (LAS) at-rest and at three critical times during active movement preparation (-1,192, -392, and 0 ms relative to expected voluntary movement onset) to probe the state of the nervous system, and measured their effect on voluntary and involuntary motor actions (finger-press and eye-blink startle reflex, respectively). Voluntary responses were facilitated by LAS presented during active preparation, leading to earlier and more forceful responses compared to control and LAS at-rest. Notably, voluntary responses were significantly facilitated on trials where the LAS was presented early during preparation (-1,192 ms). Eye-blink reflexes to the LAS at -392 ms were significantly reduced and delayed compared to blinks elicited at other time-points, indicating suppression of sub-cortical excitability. However, voluntary responses on these trials were still facilitated by the LAS. The results provide insight into the mechanisms involved in preparing anticipatory actions. Induced activation can persist in the nervous system and can modulate subsequent actions for a longer time-period than previously thought, highlighting that movement preparation is a continuously evolving process that is susceptible to external influence throughout the preparation period. Suppression of sub-cortical excitability shortly before movement onset is consistent with previous work showing corticospinal suppression which may be a necessary step before the execution of any voluntary response.

What is attention bias variability? Examining the potential roles of attention control and response time variability in its relationship with anxiety.

The present study examined the underlying role of attention control and response time variability in explaining the relationship between anxiety and two commonly computed measures of attention bias variability: 'moving average' and 'trial-level bias score' measures. Participants (final n = 195) completed measures of anxiety symptomatology, antisaccade performance (attention control), a stand-alone measure of response-time variability, and a probe task measure of attention bias. Average bias and moving average bias variability measures both recorded significant, but low split-half reliability. Both attention bias variability measures and average attention bias were associated with anxiety, and attention control. Both attention bias variability measures correlated with response time variability. Neither attention bias variability measure correlated with average attention bias. Attention control was the single significant mediator of the relationship between anxiety and the trial-level bias score measure of attention bias variability. Neither response time variability nor attention control significantly mediated the relationship between anxiety and the moving average measure of attention bias variability. No evidence was found for the mediating role of response time variability. The present findings suggest that the relationships observed between anxiety and the trial-level bias score measure of attention bias variability in particular may be attributable to the over-arching role of attention control.

The effects of left DLPFC tDCS on emotion regulation, biased attention, and emotional reactivity to negative content.

The potentiation of neural activity in lateral prefrontal regions via transcranial direct current stimulation (tDCS) can reduce patterns of biased attention for threat and may facilitate intentional emotion regulation. The current study sought to determine whether left dorsolateral prefrontal cortex tDCS, in combination with intentional down-regulation of emotional responses would reduce negative appraisals of aversive content during emotional regulation (assessed during online tDCS), reduce patterns of biased attention and attention bias variability (assessed offline), and attenuate spontaneous (uninstructed) emotional reactivity to negative content (assessed offline) above tDCS or intentional down-regulation of emotions in isolation. Healthy participants (n = 116) were allocated to one of four experimental conditions involving either active or sham tDCS, combined with an either a down-regulate or maintain emotion regulation task. Attention bias/bias variability was assessed with an attentional probe task, and emotional reactivity was assessed in a negative video viewing task. tDCS did not affect the appraisals of negative stimuli during emotion regulation, and there were no effects on attention bias/bias variability. However, tDCS did attenuate emotional reactivity. Those receiving active stimulation showed smaller elevations in negative mood in response to viewing aversive video content compared with sham. The present findings are consistent with the potential of left frontal tDCS to attenuate negative emotional reactions to aversive content but provide no support for tDCS enhancement of emotion regulation, nor its impact on attention bias or attention bias variability.