Short Interstimulus Intervals Research Articles

Exploring the characteristics of the attentional blink paradigm when used to discover concealed knowledge.

Ganis and Patnaik (Appl Psychophysiol Biofeedback 34:189-196, 2009) reported that the attentional blink paradigm using faces could be used to detect the presence of concealed knowledge. The attentional blink is defined as the inability to successfully detect the second of two target items presented within a short inter-stimulus interval. The present study tested the use of the attentional blink paradigm in a concealed knowledge test by investigating the effect that familiar faces may have on the attentional blink. Participants completed 200 trials where they were told to look for the same familiar target (Target 2; actor Brad Pitt) that was intermixed with neutral face stimuli and one other familiar face (Target 1; actor George Clooney). Target 1 was to act as the concealed knowledge as participants familiar with Target 1 would be distracted by his unannounced presence and report not seeing Target 2 thereby showing an attentional blink. Despite all participants being familiar with Target 2, an attentional blink still occurred, but with higher than normal Target 2 accuracy rates. Overall, we found support for using the AB paradigm with the concealed knowledge test; however, a possible countermeasure to the attentional blink is familiarity with Target 2 as eight of 21 participants who recognized Target 1 (the concealed knowledge) were also able to detect Target 2 on 100% of the trials where Target 1's presence should have created an attentional blink.

Frogs Jump Forward: Semantic Knowledge Influences the Perception of Element Motion in the Ternus Display.

The Ternus effect is a robust illusion of motion that produces element motion at short interstimulus intervals (ISIs; < 50 ms) and group motion at longer ISIs (> 50 ms). Previous research has shown that the nature of the stimuli (e.g., similarity, grouping), not just ISI, can influence the likelihood of perceiving element or group motion. We examined if semantic knowledge can also influence what type of illusory motion is perceived. In Experiment I, we used a modified Ternus display with pictures of frogs in a jump-ready pose facing forwards or backwards to the direction of illusory motion. Participants perceived more element motion with the forward-facing frogs and more group motion with the backward-facing frogs. Experiment 2 tested whether this effect would still occur with line drawings of frogs, or if a more life-like image was necessary. Experiment 3 tested whether this effect was due to visual asymmetries inherent in the jumping pose. Experiment 4 tested whether frogs in a "non-jumping," sedentary pose would replicate the original effect. These experiments elucidate the role of semantic knowledge in the Ternus effect. Prior knowledge of the movement of certain animate objects, in this case, frogs can also bias the perception of element or group motion.

Dysgraphia as a Mild Expression of Dystonia in Children with Absence Epilepsy.

BackgroundAbsence epilepsy (AE) is etiologically heterogeneous and has at times been associated with idiopathic dystonia.ObjectivesBased on the clinical observation that children with AE often exhibit, interictally, a disorder resembling writer’s cramp but fully definable as dysgraphia, we tested the hypothesis that in this particular population dysgraphia would represent a subtle expression of dystonia.MethodsWe ascertained the prevalence of dysgraphia in 82 children with AE (mean age 9.7) and average intelligence and compared them with 89 age-, gender- and class-matched healthy children (mean age 10.57) using tests for handwriting fluency and quality, based on which we divided patients and controls into four subgroups: AE/dysgraphia, AE without dysgraphia, controls with dysgraphia and healthy controls. We compared the blink reflex recovery cycle in children belonging to all four subgroups.ResultsWe identified dysgraphia in 17/82 children with AE and in 7/89 controls (20.7 vs 7.8%; P = 0.016) with the former having a 3.4-times higher risk of dysgraphia regardless of age and gender (odd ratio: 3.49; 95% CI 1.2, 8.8%). The AE/dysgraphia subgroup performed worse than controls with dysgraphia in one test of handwriting fluency (P = 0.037) and in most trials testing handwriting quality (P< 0.02). In children with AE/dysgraphia the blink reflex showed no suppression at short interstimulus intervals, with a difference for each value emerging when comparing the study group with the three remaining subgroups (P<0.001).ConclusionsIn children with AE, dysgraphia is highly prevalent and has a homogeneous, distinctive pathophysiological substrate consistent with idiopathic dystonia.

Normalization of sensorimotor integration by repetitive transcranial magnetic stimulation in cervical dystonia.

Previous studies indicated that sensorimotor integration and plasticity of the sensorimotor system are impaired in dystonia patients. We investigated motor evoked potential amplitudes and short latency afferent inhibition to examine corticospinal excitability and cortical sensorimotor integration, before and after inhibitory 1Hz repetitive transcranial magnetic stimulation over primary sensory and primary motor cortex in patients with cervical dystonia (n=12). Motor evoked potentials were recorded from the right first dorsal interosseous muscle after application of unconditioned transcranial magnetic test stimuli and after previous conditioning electrical stimulation of the right index finger at short interstimulus intervals of 25, 30 and 40ms. Results were compared to a group of healthy age-matched controls. At baseline, motor evoked potential amplitudes did not differ between groups. Short latency afferent inhibition was reduced in cervical dystonia patients compared to healthy controls. Inhibitory 1Hz sensory cortex repetitive transcranial magnetic stimulation but not motor cortex repetitive transcranial magnetic stimulation increased motor evoked potential amplitudes in cervical dystonia patients. Additionally, both 1Hz repetitive transcranial magnetic stimulation over primary sensory and primary motor cortex normalized short latency afferent inhibition in these patients. In healthy subjects, sensory repetitive transcranial magnetic stimulation had no influence on motor evoked potential amplitudes and short latency afferent inhibition. Plasticity of sensorimotor circuits is altered in cervical dystonia patients.

Effects of Countermeasures on P300-based Concealed Information Test with Short Inter-Stimulus Interval

본 연구에서는 관련자극이 한 개이고 자극간 제시간격이 1초인 P300 숨긴정보검사(P300 CIT)가 부분 매칭 대응수단에 영향을 받는지 검증하였으며, 대응수단의 사용을 탐지할 수 있는 방법을 탐색하였다. 네 개의 무관련자극 중 하나의 무관련자극에 특정 반응을 하는 조건(1CM 조건)과 두 개의 무관련자극에 특정 반응을 하는 조건(2CM 조건)에서 대응수단의 효과를 검증하였다. 각 조건에서 손가락 또는 발가락을 움직이는 물리적 대응수단과 마음속으로 어머니 또는 아버지의 이름을 부르는 정신적 대응수단을 사용하였다. 실험결과, 물리적 대응수단과 정신적 대응수단은 모두 P300 CIT의 결과에 큰 영향을 미치는 것으로 나타났다. 대응수단을 사용하지 않은 경우에 P300 CIT의 정확탐지율은 71%였던 반면, 물리적 대응수단을 사용한 경우에는 1CM 조건과 2CM 조건의 정확탐지율은 각각 0%와 14%였으며, 정신적 대응수단을 사용한 경우에는 1CM 조건과 2CM 조건의 정확탐지율이 모두 14%였다. ERP들 간의 상관계수로 대응수단의 탐지가능성을 평가하였다. 거짓을 말하였으나 거짓을 말하지 않은 것으로 잘못 판단된 사례들을 대상으로, 무관련자극의 ERP와 관련자극의 ERP 간 상관계수가 무관련자극의 ERP와 목표자극의 ERP 간 상관계수보다 더 큰지 확인하였다. 물리적 대응수단집단의 100%와 정신적 대응수단집단의 92%가 이러한 경우에 해당한 반면에 단순유죄집단은 33%만 이러한 양상을 보였다. ERP간 상관계수를 이용한 대응수단 사용의 탐지가능성을 논의하였다.

Olfactory processing: detection of rapid changes.

Changes in the olfactory environment have a rather poor chance of being detected. Aim of the present study was to determine, whether the same (cued) or different (uncued) odors can generally be detected at short inter stimulus intervals (ISI) below 2.5 s. Furthermore we investigated, whether inhibition of return, an attentional phenomenon facilitating the detection of new stimuli at longer ISI, is present in the domain of olfaction. Thirteen normosmic people (3 men, 10 women; age range 19-27 years; mean age 23 years) participated. Stimulation was performed using air-dilution olfactometry with 2 odors: phenylethylalcohol and hydrogen disulfide. Reaction time to target stimuli was assessed in cued and uncued conditions at ISIs of 1, 1.5, 2, and 2.5 s. There was a significant main effect of ISI, indicating that odors presented only 1 s apart are missed frequently. Uncued presentation facilitated detection at short ISIs, implying that changes of the olfactory environment are detected better than presentation of the same odor again. Effects in relation to "olfactory inhibition of return," on the other hand, are not supported by our results. This suggests that attention works different for the olfactory system compared with the visual and auditory systems.

Effects of stimulus order on discrimination sensitivity for short and long durations.

Previous studies have shown that discrimination sensitivity in 2AFC tasks depends on the presentation order of the standard and comparison stimulus. The present study examined whether this so-called Type B effect generalizes across different standard magnitudes. Therefore, Experiment 1 employed an auditory duration discrimination task with short (100 ms) and long (1,000 ms) standard durations and a constant interstimulus interval (ISI) of 1,000 ms. For both standard durations, a clear Type B effect emerged. In Experiment 2, discrimination sensitivity was assessed for short (300 ms) and long (1,000 ms) ISIs and a constant standard duration of 100 ms, in order to examine whether the Type B effect diminishes or even reverses when both stimuli are presented in rapid succession, as was suggested by previous studies. In the short, but not the long ISI condition, the Type B effect was virtually eliminated. Taken together, the present experiments suggest that the Type B effect is robust across standard magnitude, but diminishes when the time interval between both stimuli is reduced. This result pattern is discussed within the framework of the Internal Reference Model and the Sensation Weighting Model. It is also demonstrated that both models provide a quantitative account of the present results.

Participation of the classical speech areas in auditory long-term memory.

Accumulating evidence suggests that storing speech sounds requires transposing rapidly fluctuating sound waves into more easily encoded oromotor sequences. If so, then the classical speech areas in the caudalmost portion of the temporal gyrus (pSTG) and in the inferior frontal gyrus (IFG) may be critical for performing this acoustic-oromotor transposition. We tested this proposal by applying repetitive transcranial magnetic stimulation (rTMS) to each of these left-hemisphere loci, as well as to a nonspeech locus, while participants listened to pseudowords. After 5 minutes these stimuli were re-presented together with new ones in a recognition test. Compared to control-site stimulation, pSTG stimulation produced a highly significant increase in recognition error rate, without affecting reaction time. By contrast, IFG stimulation led only to a weak, non-significant, trend toward recognition memory impairment. Importantly, the impairment after pSTG stimulation was not due to interference with perception, since the same stimulation failed to affect pseudoword discrimination examined with short interstimulus intervals. Our findings suggest that pSTG is essential for transforming speech sounds into stored motor plans for reproducing the sound. Whether or not the IFG also plays a role in speech-sound recognition could not be determined from the present results.

Difference in perceptual and oculomotor responses revealed by apparent motion stimuli presented with an interstimulus interval.

To understand the mechanisms underlying visual motion analyses for perceptual and oculomotor responses and their similarities/differences, we analyzed eye movement responses to two-frame animations of dual-grating 3f5f stimuli while subjects performed direction discrimination tasks. The 3f5f stimulus was composed of two sinusoids with a spatial frequency ratio of 3:5 (3f and 5f), creating a pattern with fundamental frequency f. When this stimulus was shifted by 1/4 of the wavelength, the two components shifted 1/4 of their wavelengths and had opposite directions: the 5f forward and the 3f backward. By presenting the 3f5f stimulus with various interstimulus intervals (ISIs), two visual-motion-analysis mechanisms, low-level energy-based and high-level feature-based, could be effectively distinguished. This is because response direction depends on the relative contrast between the components when the energy-based mechanism operates, but not when the feature-based mechanism works. We found that when the 3f5f stimuli were presented with shorter ISIs (<100 ms), and 3f component had higher contrast, both perceptual and ocular responses were in the direction of the pattern shift, whereas the responses were reversed when the 5f had higher contrast, suggesting operation of the energy-based mechanism. On the other hand, the ocular responses were almost negligible with longer ISIs (>100 ms), whereas perceived directions were biased toward the direction of pattern shift. These results suggest that the energy-based mechanism is dominant in oculomotor responses throughout ISIs; however, there is a transition from energy-based to feature-tracking mechanisms when we perceive visual motion.

Olfactory speed – Temporal odor processing of paired stimuli

ObjectivesCompared to other senses, temporal perception of odors seems fairly slow. In addition it has been shown in previous studies that even not consciously perceived odors could influence our behavior. Aim of the current study therefore was to study the interstimulus interval (ISI) length, which is necessary between two repetitive stimuli to be able to perceive them separately. The additional aim focused on observing central odor processing of not perceived odorous stimuli. Materials and methods: The study was divided into three parts. In each part healthy, normosmic volunteers were included. In part I and II stimulus pairs (CO2, H2S, orange and phenyl ethyl alcohol (PEA)) were presented to the subjects via a computer-controlled olfactometer with short ISI of 0.6–9s. The decision whether one or two stimuli were perceived was recorded. In addition the influence of odor valence, trigeminallity and concentrations was observed. In part III olfactory event-related potentials (OERPs) to perceived and not-perceived odors were recorded. Results: The two stimuli of a stimulus pair were perceived separately more often with increasing ISI length. This increase was significant until an ISI between the stimuli of 4s. Odor intensity, pleasantness, trigeminallity and sex had no major influence on this. In addition we were able to observe that OERPs are less often detected in response to not perceived olfactory stimuli. However, the presence of OERP in response to not perceived stimuli in more than half of the cases indicated that even not perceived stimuli are centrally processed.

Habituation of LG-mediated tailflip in the crayfish.

Crayfish escape from threatening stimuli by tailflipping. If a stimulus is applied to the rear, crayfish escape up and forwards in a summersault maneuver that is mediated by the activation of lateral giant (LG) interneurons. The occurrence probability of LG-mediated tailflip, however, diminishes and habituates if a stimulus is repeatedly applied. Since crayfish have a relatively simple CNS with many identifiable neurons, crayfish represent a good animal to analyze the cellular basis of habituation. A reduction in the amplitude of the EPSP in the LGs, caused by direct chemical synaptic connection from sensory afferents by repetitive stimulations, is essential to bring about an inactivation of the LGs. The spike response of the LGs recovers within several minutes of habituation, but the LGs subsequently fail to spike when an additional stimulus is applied after specific periods following habituation. These results indicate that a decline in synaptic efficacy from the mechanosensory afferents recovers readily after a short delay, but then the excitability of the LGs themselves decreases. Furthermore, the processes underlying habituation are modulated depending on a social status. When two crayfish encounter each other, a winner-loser relationship is established. With a short interstimulus interval of 5s, the rate of habituation of the LG in both socially dominant and subordinate crayfish becomes lower than in socially isolated animals. Serotonin and octopamine affect this social status-dependent modulation of habituation by means of activation of downstream second messenger system of cAMP and IP3 cascades, respectively.

Assessment of nonlinear interactions in event-related potentials elicited by stimuli presented at short interstimulus intervals using single-trial data.

The recording of brain event-related potentials (ERPs) is a widely used technique to investigate the neural basis of sensory perception and cognitive processing in humans. Due to the low magnitude of ERPs, averaging of several consecutive stimuli is typically employed to enhance the signal to noise ratio (SNR) before subsequent analysis. However, when the temporal interval between two consecutive stimuli is smaller than the latency of the main ERP peaks, i.e., when the stimuli are presented at a fast rate, overlaps between the corresponding ERPs may occur. These overlaps are usually dealt with by assuming that there is a simple additive superposition between the elicited ERPs and consequently performing algebraic waveform subtractions. Here, we test this assumption rigorously by providing a statistical framework that examines the presence of nonlinear additive effects between overlapping ERPs elicited by successive stimuli with short interstimulus intervals (ISIs). The results suggest that there are no nonlinear additive effects due to the time overlap per se but that, for the range of ISIs examined, the second ERP is modulated by the presence of the first stimulus irrespective of whether there is time overlap or not. In other words, two ERPs that overlap in time can still be written as an addition of two ERPs but with the second ERP being different from the first. This difference is also present in the case of nonoverlapping ERPs with short ISIs. The modulation effect elicited on the second ERP by the first stimulus is dependent on the ISI value.

N170 adaptation effect for repeated faces and words

Using ERP adaptation paradigms, studies have shown that the N170 adaptation effect is a stable phenomenon for both faces and words. However, the N170 adaptation effect for repeated identity remains unclear, so we have addressed this with two experiments. In Experiment 1, we investigated the face-related N170 repeated adaptation effect in a short interstimulus interval (ISI) and found that the N170 response elicited by faces was smaller when preceded by a same face adaptor than by another face adaptor. Experiment 2 addressed whether this repeated N170 adaptation effect generalizes to words. For the first time, the results indicated that the N170 response elicited by words was larger with a different word as an adaptor relative to the same word as an adaptor. Our results demonstrate that the face-related N170 response is sensitive to visual face features and extend the characteristics of N170 with the sensitivity to repeated items to other familiar objects of expertise (i.e. words). The results also suggest that there are some common characteristics between faces and words in the early perceptual processing.

Introduction and validation of a less painful algorithm to estimate the nociceptive flexion reflex threshold

The nociceptive flexion reflex (NFR) is a widely used tool to investigate spinal nociception for scientific and diagnostic purposes, but its clinical use is currently limited due to the painful measurement procedure, especially restricting its applicability for patients suffering from chronic pain disorders. Here we introduce a less painful algorithm to assess the NFR threshold. Application of this new algorithm leads to a reduction of subjective pain ratings by over 30% compared to the standard algorithm. We show that the reflex threshold estimates resulting from application of the new algorithm can be used interchangeably with those of the standard algorithm after adjusting for the constant difference between the algorithms. Furthermore, we show that the new algorithm can be applied at shorter interstimulus intervals than are commonly used with the standard algorithm, since reflex threshold values remain unchanged and no habituation effects occur when reducing the interstimulus interval for the new algorithm down to 3s. Finally we demonstrate the utility of the new algorithm to investigate the modulation of nociception through different states of attention. Taken together, the here presented new algorithm could increase the utility of the NFR for investigation of nociception in subjects who were previously not able to endure the measurement procedure, such as chronic pain patients.

The 3-Second Rule in Hereditary Pure Cerebellar Ataxia: A Synchronized Tapping Study

The ‘3-second rule’ has been proposed based on miscellaneous observations that a time period of around 3 seconds constitutes the fundamental unit of time related to the neuro-cognitive machinery in normal humans. The aim of paper was to investigate the temporal processing in patients with spinocerebellar ataxia type 6 (SCA6) and SCA31, pure cerebellar types of spinocerebellar degeneration, using a synchronized tapping task. Seventeen SCA patients (11 SCA6, 6 SCA31) and 17 normal age-matched volunteers participated. The task required subjects to tap a keyboard in synchrony with sequences of auditory stimuli presented at fixed interstimulus intervals (ISIs) between 200 and 4800 ms. In this task, the subjects required non-motor components to estimate the time of forthcoming tone in addition to motor components to tap. Normal subjects synchronized their taps to the presented tones at shorter ISIs, whereas as the ISI became longer, the normal subjects displayed greater latency between the tone and the tapping (transition zone). After the transition zone, normal subjects pressed the button delayed relative to the tone. On the other hand, SCA patients could not synchronize their tapping with the tone even at shorter ISIs, although they pressed the button delayed relative to the tone earlier than normal subjects did. The earliest time of delayed tapping appearance after the transition zone was 4800 ms in normal subjects but 1800 ms in SCA patients. The span of temporal integration in SCA patients is shortened compared to that in normal subjects. This could represent non-motor cerebellar dysfunction in SCA patients.

Enhanced motor cortex excitability after spinal cord injury.

Enhanced motor cortex excitability after spinal cord injury.

49.: The fampridine upper limb study (FULS)

Modified-release 4-aminopyridine (fampridine) is licensed in Australia for the symptomatic treatment of walking disability in patients with multiple sclerosis (MS). Its potential for use in other neurological domains, its mode of action, and the reasons for widely variable responses in treated patients remain unknown. This study aims to test the following hypotheses: (1) modified-release fampridine is associated with improvements in upper limb impairment in patients with multiple sclerosis, and (2) objective electrophysiological measures differ between patients on and off treatment, and can potentially be used to differentiate clinical responders and non-responders. We conducted two substudies. Substudy 1 is a randomised, double-blind, placebo-controlled trial in patients with MS and upper limb impairment. Clinical and electrophysiological measurements are made at baseline, conclusion and on three occasions while participants are taking fampridine-modified release or placebo. Substudy 2 is a single-blind study in patients already taking fampridine for walking disability. Clinical and electrophysiological measurements are made in patients while on (twice) and off (once) the drug by a blinded assessor. Clinical measurements are nine-hole peg test, upper limb grip strength, sensory discrimination capacity, visual acuity and contrast sensitivity, and modified fatigue impact scale. Electrophysiological measurements were resting motor threshold, motor evoked potential recruitment curves, short interstimulus intervals paired pulse transcranial magnetic stimulation (TMS), median nerve somatosensory evoked potentials, visual evoked potentials, and median nerve conduction study. The primary outcome measure is clinical response to fampridine as measured by performance on the nine-hole peg test. Secondary outcome measures are correlation between clinical and electrophysiological measures in responders as compared with non-responders, changes in upper limb grip strength, visual acuity and sensory discrimination capacity, and changes in modified fatigue impact scale score. Our hypothesis is that clinical responders to fampridine will show increased motor pathway recruitment and cortical excitability with TMS measures, with improvements in latency and amplitude of evoked potential responses. This novel study seeks to determine whether fampridine can have beneficial effects in domains other than ambulation. By combining clinical and electrophysiological measures, we seek to better understand the mode of action of fampridine as a symptomatic therapy for MS and the reasons for the wide observed variation in clinical response.

Topography of retinal recovery processes in humans.

BackgroundThe purpose of this study was to examine retinal recovery processes to pographically by the application of three flash sequences with specific interstimulus intervals.MethodsTwelve healthy subjects underwent multifocal electroretinography with a light-emitting diode stimulator. Every flash sequence consisted of three flashes with 25 msec between the first and the second flash and 35 msec between the second and the third flash. The interval between the third and the first flash of the next step was 85 msec. The interstimulus interval-dependent amplitude reductions of the multifocal electroretinographic response for these three intervals yielded three data points that were used to determine the complete curve of the recovery kinetics.ResultsAmplitude reductions were higher with shorter interstimulus intervals. The mean half-life periods of the recovery kinetics for the different concentric rings and all subjects were: ring 1, 29.3±5.9 msec; ring 2, 24.2±6.4 msec; ring 3, 23±4.1 msec; ring 4, 23.1±4.6 msec; and ring 5, 22.3±4.4 msec. The differences between the first and all other rings were statistically significant (P<0.05).ConclusionThe kinetics of the amplitude recovery after short interstimulus intervals showed a spatial distribution, with faster recovery toward the macular periphery.

Echoic memory: investigation of its temporal resolution by auditory offset cortical responses.

Previous studies showed that the amplitude and latency of the auditory offset cortical response depended on the history of the sound, which implicated the involvement of echoic memory in shaping a response. When a brief sound was repeated, the latency of the offset response depended precisely on the frequency of the repeat, indicating that the brain recognized the timing of the offset by using information on the repeat frequency stored in memory. In the present study, we investigated the temporal resolution of sensory storage by measuring auditory offset responses with magnetoencephalography (MEG). The offset of a train of clicks for 1 s elicited a clear magnetic response at approximately 60 ms (Off-P50m). The latency of Off-P50m depended on the inter-stimulus interval (ISI) of the click train, which was the longest at 40 ms (25 Hz) and became shorter with shorter ISIs (2.5∼20 ms). The correlation coefficient r2 for the peak latency and ISI was as high as 0.99, which suggested that sensory storage for the stimulation frequency accurately determined the Off-P50m latency. Statistical analysis revealed that the latency of all pairs, except for that between 200 and 400 Hz, was significantly different, indicating the very high temporal resolution of sensory storage at approximately 5 ms.

Modulation of short-latency afferent inhibition depends on digit and task-relevance.

Short-latency afferent inhibition (SAI) occurs when a single transcranial magnetic stimulation (TMS) pulse delivered over the primary motor cortex is preceded by peripheral electrical nerve stimulation at a short inter-stimulus interval (∼20–28 ms). SAI has been extensively examined at rest, but few studies have examined how this circuit functions in the context of performing a motor task and if this circuit may contribute to surround inhibition. The present study investigated SAI in a muscle involved versus uninvolved in a motor task and specifically during three pre-movement phases; two movement preparation phases between a “warning” and “go” cue and one movement initiation phase between a “go” cue and EMG onset. SAI was tested in the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles in twelve individuals. In a second experiment, the origin of SAI modulation was investigated by measuring H-reflex amplitudes from FDI and ADM during the motor task. The data indicate that changes in SAI occurred predominantly in the movement initiation phase during which SAI modulation depended on the specific digit involved. Specifically, the greatest reduction in SAI occurred when FDI was involved in the task. In contrast, these effects were not present in ADM. Changes in SAI were primarily mediated via supraspinal mechanisms during movement preparation, while both supraspinal and spinal mechanisms contributed to SAI reduction during movement initiation.