The Effect of Two Methods of Transcranial Direct Current Stimulation (tDCS) and Stimulus-Response Asynchrony on Backward-Compatibility Effect in Mental Fatigue Conditions

. Introduction: The present study aimed to investigate the effect of anodal and cathodal brain tDCS and stimulus-response asynchrony on the backward-compatibility effect (BCE) in conditions of acute mental fatigue.Methods: The participants were 39 boys (20 to 24 years old). The instruments included the informed consent form, the Edinburgh handedness questionnaire, the dual reaction time instrument, the Stroop software, the visual analog scale to evaluate fatigue severity (VAS-F), and the tDCS device. The participants in the pre-test were tested in two conditions of non-fatigue and mental fatigue with a dual reaction time instrument. The tests consisted of two three-choice visual stimulus-response (letters and colors) with ten different stimulus onset asynchronies (SOAs). Then the subjects were randomly assigned to three Anodal, Cathodal, and Sham stimulation groups. The intervention consisted of four consecutive 20-minute sessions of tDCS stimulation on the DLPFC area. One day and four days after the last stimulation session, the tests were repeated. For inferential data analysis, Mixed Model ANOVA and One-way ANOVA tests were used at a significance level of 0.05.Results: The results showed that there is a difference between different SOAs in response time to the first stimulus (RT1) which is a representation of backward adaptation, and at lower SOAs, the RT1 is shorter. Also, there is a difference in RT1 at low SOAs between fatigued and non-fatigued conditions. However, the effect of cathodal and anodal tDCS on RT1 was very small.Conclusion: In general, the results showed that at least some central aspects related to the response can be processed in parallel. Fatigue also affects this parallel processing

The Effect of Brain Anodal and Cathodal Transcranial Direct Current Stimulation on Psychological Refractory Period at Different Stimulus-Onset Asynchrony in Non-Fatigue and Mental Fatigue Conditions

The psychological refractory period (PRP) effect occurs when two stimuli that require separate responses are presented sequentially, particularly with a short and variable time interval between them. Fatigue is a suboptimal psycho-physiological state that leads to changes in strategies. In recent years, numerous studies have investigated the effects of transcranial direct current stimulation (tDCS) on motor control. The present study aimed to investigate the effects of two tDCS methods, anodal and cathodal, on PRP in ten different conditions of stimulus-onset asynchronies (SOAs) under non-fatigue and mental fatigue conditions. The participants involved 39 male university students aged 19 to 25 years. In the pre-test, they were assessed using the PRP measurement tool under both non-fatigue and mental fatigue conditions. The mental fatigue was induced by a 30-min Stroop task. The test consisted of two stimuli with different SOAs (50, 75, 100, 150, 300, 400, 600, 900, 1200, and 1500 ms). The first was a visual stimulus with three choices (letters A, B, and C). After a random SOA, the second stimulus, a visual stimulus with three choices (colors red, yellow, and blue), was presented. Subsequently, participants were randomly assigned to the anodal, cathodal, and sham stimulation groups and underwent four consecutive sessions of tDCS stimulation. In the anodal and cathodal stimulation groups, 20 min of tDCS stimulation were applied to the PLPFC area in each session, while in the sham group, the stimulation was artificially applied. All participants were assessed using the same measurement tools as in the pre-test phase, in a post-test phase one day after the last stimulation session, and in a follow-up phase four days after that. Inferential statistics include mixed ANOVA, one-way ANOVA, independent, and dependent t-tests. The findings indicated that the response time to the second stimulus was longer at lower SOAs. However, there was no significant difference between the groups in this regard. Additionally, there was no significant difference in response time to the second stimulus between the fatigue and non-fatigue conditions, or between the groups. Therefore, tDCS had no significant effect. There was a significant difference between mental fatigue and non-fatigue conditions in the psychological refractory period. Moreover, at lower SOAs, the PRP was longer than at higher SOAs. In conditions of fatigue, the active stimulation groups (anodal and cathodal) performed better than the sham stimulation group at higher SOAs. Considering the difference in response to both stimuli at different SOAs, some central aspects of the response can be simultaneously parallel. Fatigue also affects parallel processing. This study supports the response integration phenomenon in PRP, which predicts that there will be an increase in response time to the first stimulus as the interval between the presentation of the two stimuli increases. This finding contradicts the bottleneck model. In this study, the effectiveness of cathodal and anodal tDCS on response time to the second stimulus and PRP was found to be very small

The Effect Foreperiod and Time Intervals between Stimuli on the Psychological Refractory Period: Evidence for Preparation

Given the importance of preparation to respond to two stimuli in different sport conditions, the aim of this study was to investigate the effect of foreperiod and time intervals between two stimuli on psychological refractory period (PRP) in athletes. This study was semi-experimental with a within-group design and fundamental-applied in terms of objectives. 50 male athlete students of Shahid Chamran University of Ahvaz (age range 22.47±1.45 years) were selected by convenience sampling method. A five-core processor ASUS notebook, Edinburgh Handedness Questionnaire, software and hardware to measure the psychological refractory period were used in this study. Participants responded to two visual (selective) stimuli that were presented with short time intervals as quickly as possible. Tests were conducted in dual tasks and single tasks in foreperiods of 1,2,4,8 s and time intervals of 100, 250, 500, 800 ms randomly. The data were analyzed using mean, standard deviation, within group analysis of variance at significance level (P<0.05). The results showed that the effects of foreperiod and the stimuli intervals were significant. The foreperiod of 1s and interval of 100 ms had the most psychological refractory period and foreperiod of 8s and interval of 800 ms had the lowest psychological refractory period. This study showed that the pattern of psychological refractory period was affected by experimental manipulation of the preparation processes when recognizing the stages of information processing. Contrary to the common belief that preparation time operates on premotor processes, in the present study preparation time operates on late motion processes and confirms the existence of processing bottlenecks in dual task

The Effect of Handedness and Task Difficulty on Effective Target Width and Temporal Accuracy in Fitts’ Speed-Accuracy Tradeoff Task

The aim of this study was to investigate the effect of handedness and task difficulty on effective target width and temporal accuracy of the Fitts’ speed-accuracy tradeoff task. The present study was semi-experimental and the tools used included Edinburgh handedness questionnaire, light pen, speed-accuracy measurement device, laptop, chronometer, and metronome. The statistical population consisted of students aged between 14 and 15. The sample included 20 students who participated in this study by convenience sampling method. They were divided into two groups: left-hand and right-hand (each group 10 subjects). Each participant performed 4 trials (each trial 30 seconds) of dual target tapping task in rhythm with the metronome sound. The trials consisted of two easy and difficult tasks and each subject performed each task with dominant and not-dominant hands in rhythm with the metronome sound set up at 300 milliseconds. For statistical analysis of data, variance analysis with repeated measures was used at the significance level of 0.05. The results showed that in dominant hand, the handedness and difficulty of the task had no significant effect on the effective width of the target (P=0.973, P=0.611). Also, the handedness did not affect the average time lag (P=0.135, P=0.785), but in non-dominant hand, the average time lag was more for the difficult task than the simple task (P=0.001). In difficult tasks, participants seem to be trying to keep the spatial error rate constant by reducing the speed of the movement and to sacrifice speed for the spatial accuracy. Also, the time error (mean lag) is more influenced by the difficulty of the task than the handedness