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Background Many studies have attempted to identify the sources of interindividual variability in response to theta-burst stimulation (TBS). However, these studies have been limited by small sample sizes, leading to conflicting results. Objective/Hypothesis This study brought together over 60 TMS researchers to form the ‘Big TMS Data Collaboration’, and create the largest known sample of individual participant TBS data to date. The goal was to enable a more comprehensive evaluation of factors driving TBS response variability. Methods 118 corresponding authors of TMS studies were emailed and asked to provide deidentified individual TMS data. Mixed-effects regression investigated a range of individual and study level variables for their contribution to iTBS and cTBS response variability. Results 430 healthy participants’ TBS data was pooled across 22 studies (mean age = 41.9; range = 17–82; females = 217). Baseline MEP amplitude, age, target muscle, and time of day significantly predicted iTBS-induced plasticity. Baseline MEP amplitude and timepoint after TBS significantly predicted cTBS-induced plasticity. Conclusions This is the largest known study of interindividual variability in TBS. Our findings indicate that a significant portion of variability can be attributed to the methods used to measure the modulatory effects of TBS. We provide specific methodological recommendations in order to control and mitigate these sources of variability.

A new method of calculating attentional bias from the dot-probe task measures fluctuations in bias towards and away from emotional stimuli over time using trial level bias score metrics. We assessed the stability and reliability of traditional attentional bias scores and trial level bias score measures of attentional bias across time in two five-block dot-probe task experiments in non-clinical samples. In experiments 1 and 2, both traditional attentional bias scores and trial level bias score measures of attentional bias did not habituate/decrease across time. In general, trial level bias score metrics (i.e., attention bias variability as well as the mean biases toward and away from threat) were more reliable than the traditional attention bias measure. This pattern was observed across both experiments. The traditional bias score, however, did improve in reliability in the later blocks of the fearful face dot-probe task. Although trial level bias score measures did not habituate and were more reliable across blocks, these measures did not correlate with state or trait anxiety. On the other hand, trial level bias score measures were strongly correlated with general reaction time variability—and after controlling for this effect no longer superior in reliability in comparison to the traditional attention bias measure. We conclude that general response variability should be removed from trial level bias score measures to ensure that they truly reflect attention bias variability.

Response variability between individuals (interindividual variability) and within individuals (intraindividual variability) is an important issue in the transcranial magnetic stimulation (TMS) literature. This has raised questions of the validity of TMS to assess changes in corticospinal excitability (CSE) in a predictable and reliable manner. Several participant-specific factors contribute to this observed response variability with a current lack of consensus on the degree each factor contributes. This highlights a need for consistency and structure in reporting study designs and methodologies. Currently, there is no summarized review of the participant-specific factors that can be controlled and may contribute to response variability. This systematic review aimed to develop a checklist of methodological measures taken by previously published research to increase the homogeneity of participant selection criteria, preparation of participants before experimental testing, participant scheduling, and the instructions given to participants throughout experimental testing to minimize their effect on response variability. Seven databases were searched in full. Studies were included if CSE was measured via TMS and included methodological measures to increase the homogeneity of the participants. Eighty-four studies were included. Twenty-three included measures to increase participant selection homogeneity, 21 included measures to increase participant preparation homogeneity, while 61 included measures to increase participant scheduling and instructions during experimental testing homogeneity. These methodological measures were summarized into a user-friendly checklist with considerations, suggestions, and rationale/justification for their inclusion. This may provide the framework for further insights into ways to reduce response variability in TMS research.

Adolescence represents a time of significant change in emotional processes. To what extent these changes in emotional processes are similar or distinct in adolescents relative to young adults remains largely unknown. The current study tested whether variation in reaction times to emotional stimuli could distinguish between different phases of emotional development. Ex-Gaussian parameters mu, sigma and tau were computed, in addition to mean, median and standard deviation (SD) in reaction times (RT) during an emotional go/nogo-paradigm with fearful, happy and calm facial expressions in 377 participants, 6 to 30 years of age. Mean RT showed consistent slowing to fearful expressions relative to both calm and positive cues across development, but mu revealed that this pattern was more specific to adolescence. In contrast, increased variability to fearful expressions relative to both happy and calm ones was captured by SD and tau and specific to young adulthood. The findings suggest that in adolescents and young adults response speed and variability are differentially modulated by negative emotional information, possibly reflecting distinct phases of the development of emotional processing. Understanding age specific changes in negative emotional processes ultimately may inform our understanding of the emergence of different psychopathologies in adolescence and in early adulthood.

Researchers have demonstrated the efficacy of picture prompts on the acquisition of intraverbals (Coon & Miguel in Journal of Applied Behavior Analysis, 45, 657–666, 2012; Goldsmith, LeBlanc, & Sautter in Research in Autism Spectrum Disorders, 1, 1–13, 2007; Ingvarsson & Hollobaugh in Journal of Applied Behavior Analysis, 44, 659–664, 2011; Ingvarsson & Le in The Analysis of Verbal Behavior, 27, 75–93, 2011; Miguel, Petursdottir, & Carr in The Analysis of Verbal Behavior, 21, 27–41, 2005; Partington & Bailey in The Analysis of Verbal Behavior, 11, 9–18, 1993). However, no one (to our knowledge) has determined the effects of picture prompts on the variability of responding during intraverbal categorization. We evaluated the use of a scenic picture prompt on response variability during the acquisition of intraverbal categorization with 4 children diagnosed with autism. All children mastered the task and initially demonstrated varied responding. However, responding eventually became invariant for all children. These results demonstrate the efficacy of a scenic picture prompt for teaching children with autism intraverbal categorization and for producing initial response variability. Additional research should be conducted to determine teaching procedures that promote continued varied responding for individuals with autism.

Individuals with complex communication needs are likely to experience considerable difficulties and challenges with everyday communication interactions due to limited use and understanding of natural speech. In this editorial, we review the nature of complex communication needs, describe the wide range of individuals who may experience such needs, and provide a brief history of behavioral approaches to addressing these needs. We also highlight the six papers in this special issue that contribute to the further understanding of the use of behavioral intervention approaches for addressing complex communication needs. These papers include one conceptual overview of aided augmentative and alternative communication (AAC) interventions for individuals with complex communication needs, four intervention studies addressing a range of communicative topographies (i.e., vocal speech, AAC, and a social messaging app), and one systematic review examining interventions that promote communicative response variability. These six papers highlight the diversity of complex communication needs and emphasize the importance of examining the efficacy of a wide range of individualized behavioral approaches that are matched to specific needs and goals.

Interventions aimed at increasing communicative response variability hold particular importance for individuals with autism spectrum disorders (ASD). Several procedures have been demonstrated in the applied and translational literature to increase response variability. However, little is known about the relationship between reinforcer magnitude and response variability. In the basic literature, Doughty, Giorno, and Miller evaluated the effects of reinforcer magnitude on behavioral variability by manipulating reinforcer magnitude across alternating relative frequency threshold contingencies, with results suggesting that larger reinforcers induced repetitive responding. The purpose of this study was to translate Doughty et al.’s findings to evaluate the relative effects of different magnitudes of reinforcement on communicative response variability in children with ASD. A Lag 1 schedule of reinforcement was in place during each condition within an alternating treatments design. Magnitudes of reinforcement contingent on variable communicative responding were manipulated across the two conditions. Inconsistent with basic findings, the results showed higher levels of variable communicative responding associated with the larger magnitude of reinforcement. These outcomes may have potential implications for interventions aimed at increasing response variability in individuals with ASD, as well as future research in this area.

There is evidence from human twin and family studies as well as mouse and rat selection experiments that there are considerable interindividual differences in the response of cardiorespiratory fitness (CRF) and other cardiometabolic traits to a given exercise programme dose. We developed this consensus statement on exercise response variability following a symposium dedicated to this topic. There is strong evidence from both animal and human studies that exercise training doses lead to variable responses. A genetic component contributes to exercise training response variability.In this consensus statement, we (1) briefly review the literature on exercise response variability and the various sources of variations in CRF response to an exercise programme, (2) introduce the key research designs and corresponding statistical models with an emphasis on randomised controlled designs with or without multiple pretests and post-tests, crossover designs and repeated measures designs, (3) discuss advantages and disadvantages of multiple methods of categorising exercise response levels—a topic that is of particular interest for personalised exercise medicine and (4) outline approaches that may identify determinants and modifiers of CRF exercise response. We also summarise gaps in knowledge and recommend future research to better understand exercise response variability.

Skill learning is fundamental to the acquisition of many complex behaviors that emerge during development. For example, years of practice give rise to perceptual improvements that contribute to mature speech and language skills. While fully honed learning skills might be thought to offer an advantage during the juvenile period, the ability to learn actually continues to develop through childhood and adolescence, suggesting that the neural mechanisms that support skill learning are slow to mature. To address this issue, we asked whether the rate and magnitude of perceptual learning varies as a function of age as male and female gerbils trained on an auditory task. Adolescents displayed a slower rate of perceptual learning compared with their young and mature counterparts. We recorded auditory cortical neuron activity from a subset of adolescent and adult gerbils as they underwent perceptual training. While training enhanced the sensitivity of most adult units, the sensitivity of many adolescent units remained unchanged, or even declined across training days. Therefore, the average rate of cortical improvement was significantly slower in adolescents compared with adults. Both smaller differences between sound-evoked response magnitudes and greater trial-to-trial response fluctuations contributed to the poorer sensitivity of individual adolescent neurons. Together, these findings suggest that elevated sensory neural variability limits adolescent skill learning.SIGNIFICANCE STATEMENTThe ability to learn new skills emerges gradually as children age. This prolonged development, often lasting well into adolescence, suggests that children, teens, and adults may rely on distinct neural strategies to improve their sensory and motor capabilities. Here, we found that practice-based improvement on a sound detection task is slower in adolescent gerbils than in younger or older animals. Neural recordings made during training revealed that practice enhanced the sound sensitivity of adult cortical neurons, but had a weaker effect in adolescents. This latter finding was partially explained by the fact that adolescent neural responses were more variable than in adults. Our results suggest that one mechanistic basis of adult-like skill learning is a reduction in neural response variability.

A common behavioral marker of optimal attention focus is faster responses or reduced response variability. Our previous study found two dominant brain states during sustained attention, and these states differed in their behavioral accuracy and reaction time (RT) variability. However, RT distributions are often positively skewed with a long tail (i.e., reflecting occasional slow responses). Therefore, a larger RT variance could also be explained by this long tail rather than the variance around an assumed normal distribution (i.e., reflecting pervasive response instability based on both faster and slower responses). Resolving this ambiguity is important for better understanding mechanisms of sustained attention. Here, using a large dataset of over 20,000 participants who performed a sustained attention task, we first demonstrated the utility of the exGuassian distribution that can decompose RTs into a strategy factor, a variance factor, and a long tail factor. We then investigated which factor(s) differed between the two brain states using fMRI. Across two independent datasets, results indicate unambiguously that the variance factor differs between the two dominant brain states. These findings indicate that ‘suboptimal’ is different from ‘slow’ at the behavior and neural level, and have implications for theoretically and methodologically guiding future sustained attention research.

The purpose of the current study was to assess meaningful variability in visual-perceptual skills using a standardized assessment of visual perception, the Test of Visual Perceptual Skills (TVPS), across children with and without autism spectrum disorder (ASD). In addition to assessing overall accuracy across subtests of the TVPS, we also assessed response variability at the item-level, and the linear relationship between quantitative measures of ASD symptoms, task performance, and item-level variance. We report a significant linear relationship between ASD features and performance on the TVPS Figure Ground subtest. Additionally, results of an item-level analysis point to a significant relationship between within-task variability on the Figure Ground subtest and quantitative ASD traits, with a less variable response pattern being associated with increased ASD symptoms. Findings presented here suggest variability in perceptual processing across ASD may be influenced by individual differences in trait distribution.

The different responses of humans to an apparently equivalent stimulus are called interindividual response variability. This phenomenon has gained more and more attention in research in recent years. The research field of exercise-cognition has also taken up this topic, as shown by a growing number of studies published in the past decade. In this perspective article, we aim to prompt the progress of this research field by (i) discussing the causes and consequences of interindividual variability, (ii) critically examining published studies that have investigated interindividual variability of neurocognitive outcome parameters in response to acute physical exercises, and (iii) providing recommendations for future studies, based on our critical examination. The provided recommendations, which advocate for a more rigorous study design, are intended to help researchers in the field to design studies allowing them to draw robust conclusions. This, in turn, is very likely to foster the development of this research field and the practical application of the findings.

This study examined whether girls and boys with ADHD show similar impairments in cognitive control from childhood into adolescence and the developmental relationship between cognitive control and ADHD symptoms. Participants include 8–17-year-old children with ADHD (n = 353, 104 girls) and typically developing (TD) controls (n = 241, 86 girls) with longitudinal data obtained from n = 137. Participants completed two go/no-go (GNG) tasks that varied in working memory demand. Linear mixed-effects models were applied to compare age-related changes in cognitive control for each GNG task among girls and boys with ADHD and TD controls and in relation to ADHD symptoms. Boys with ADHD showed impaired response inhibition and increased response variability across tasks. In contrast, girls with ADHD showed impaired response inhibition only with greater working memory demands whereas they displayed increased response variability regardless of working memory demands. Analysis of age-related change revealed that deficits in cognitive control under minimal working memory demands increase with age among girls with ADHD and decrease with age among boys with ADHD. In contrast, deficits in cognitive control with greater working memory demands decrease with age among both boys and girls with ADHD compared to TD peers. Among children with ADHD poor response inhibition during childhood predicted inattentive symptoms in adolescence and was associated with less age-related improvement in inattentive symptoms. These findings suggest that girls and boys with ADHD show differential impairment in cognitive control across development and response inhibition in childhood may be an important predictor of ADHD symptoms in adolescence.

Using event-related potentials (ERPs), we investigated the effects of passive heat stress and recovery on the human cognitive function with Flanker tasks, involving congruent and incongruent stimuli. We hypothesized that modulation of the peak amplitude and latency of the P300 component in ERP waveforms would differ with task difficulty during passive heat stress and recovery. Subjects performed the Flanker tasks before (Pre), at the end of whole body heating (Heat: internal temperature increase of ~1.2°C from the pre-heat baseline), and after the internal temperature had returned to the pre-heat baseline (Recovery). The internal temperature was regulated by a tube-lined suit by perfusing 50°C water for heat stress and 25°C water for recovery immediately after the heat stress. Regardless of task difficulty, the reaction time (RT) was shortened during Heat rather than Pre and Recovery, and standard deviations of RT (i.e., response variability) were significantly smaller during Heat than Pre. However, the peak amplitudes of the P300 component in ERPs, which involved selective attention, expectancy, and memory updating, were significantly smaller during Heat than during Pre, suggesting the impairment of neural activity in cognitive function. Notably, the peak amplitudes of the P300 component were higher during Recovery than during Heat, indicating that the impaired neural activity had recovered after sufficient whole-body cooling. An indicator of the stimulus classification/evaluation time (peak latency of P300) and the RT were shortened during Heat stress, but such shortening was not noted after whole-body cooling. These results suggest that hyperthermia affects the human cognitive function, reflected by the peak amplitude and latency of the P300 component in ERPs during the Flanker tasks, but sufficient treatment such as whole-body cooling performed in this study can recover those functions.

In the present study, experimenters evaluated the influence of lag schedules of reinforcement in combination with accurate and inaccurate (complete and incomplete) rules on the response variability of naming category items for typically developing preschoolers in a group format. Results showed that when lag schedules were introduced with 2 categories, response variability generalized to the third category. Furthermore, after participants experienced the lag schedule, variability persisted when the contingency no longer required variability. Participants continued to vary their responses unless the rule and contingency required them to repeat responses. We discuss potential clinical applications of using lag schedules in a group format and including rules during teaching, as well as directions for future research in this area.

Serial dependence is the effect in which the immediately preceding trial influences participants' responses to the current stimulus. But for how long does this bias last in the absence of interference from other stimuli? Here, we had 20 healthy young adult participants (12 women) perform a coincident timing task using different inter-trial intervals to characterize the serial dependence effect as the time between trials increases. Our results show that serial dependence abruptly decreases from 0.1 s to 1 s inter-trial interval, but it remains pronounced after that for up to 8 s. In addition, participants' response variability slightly decreases over longer intervals. We discuss these results in light of recent models suggesting that serial dependence might rely on a short-term memory trace kept through changes in synaptic weights, which might explain its long duration and apparent stability over time.

The aim of the current study was to examine the association between cardiorespiratory fitness and electroencephalogram-based neural oscillations, using midfrontal theta, during an inhibitory control task in children. One-hundred seventy-one school-aged children (mean age = 8.9 ± 0.6 years; 46% girls) were recruited. Cardiorespiratory fitness was assessed by a test of maximal oxygen consumption (VO2peak ) while inhibitory control performance was measured via a modified flanker task with an electroencephalogram. Behavioral findings demonstrated that higher cardiorespiratory fitness was associated with higher response accuracy regardless of task difficulty as well as lower response variability during trials with lower cognitive demand. Neuroelectric outcomes revealed that higher cardiorespiratory fitness was correlated with smaller modulation of theta (4-7 Hz) oscillatory power regardless of task difficulty. Collectively, the current findings indicate that higher cardiorespiratory fitness is associated with better performance on a task that modulates inhibitory control, signified by higher, and more stable, task performance. More importantly, higher childhood cardiorespiratory fitness is associated with better top-down control and cortical communication, as reflected by midfrontal theta. Such findings support the critical role of cardiorespiratory fitness in brain health during childhood.

Members (behaviors) of a response class are equivalent in that they produce the same functional reinforcer. Oftentimes, some members of a response class occur at higher rates than others. This can be problematic when the members that occur at high rates are socially inappropriate (e.g., self-injury, aggression, or disruption). The participant in this study was a 16-year-old female diagnosed with autism spectrum disorder who demonstrated aggression, one-word mands, and mands with autoclitic frames. In a series of contingency reversals, we placed 2 behaviors on extinction (e.g., aggression and one-word mands), which resulted in extinction-induced variability. Capitalizing on extinction-induced variability, we reinforced a different behavior (e.g., mands with autoclitic frames). The results confirmed that (a) the rate of responding for each topography was a function of extinction-induced response variability and differential reinforcement and (b) all response topographies belonged to the same response class. These results provide empirical support for the use of extinction-induced variability to differentially increase the rate of socially appropriate behaviors while decreasing socially inappropriate behaviors that belong to the same response class.

Most current sequential sampling models have random between-trial variability in their parameters. These sources of variability make the models more complex in order to fit response time data, do not provide any further explanation to how the data were generated, and have recently been criticised for allowing infinite flexibility in the models. To explore and test the need of between-trial variability parameters we develop a simple sequential sampling model of N-choice speeded decision making: the racing diffusion model. The model makes speeded decisions from a race of evidence accumulators that integrate information in a noisy fashion within a trial. The racing diffusion does not assume that any evidence accumulation process varies between trial, and so, the model provides alternative explanations of key response time phenomena, such as fast and slow error response times relative to correct response times. Overall, our paper gives good reason to rethink including between-trial variability parameters in sequential sampling models.

Despite the growing interest in the use of transcranial direct current stimulation (tDCS) for the modulation of human cognitive function, there are contradictory findings regarding the cognitive benefits of this technique. Inter-individual response variability to tDCS may play a significant role. We explored the effects of anodal versus sham tDCS over the left prefrontal cortex (LPFC) on working memory performance, taking into account the inter-individual variability. Twenty-nine healthy volunteers received an ‘offline’ anodal tDCS (1.5 mA, 15 min) to the left prefrontal cortex (F3 electrode site) in an intra-individual, cross-over, sham-controlled experimental design. n-back and Sternberg task performance was assessed before (baseline), immediately after tDCS administration (T1) and 5 min post-T1 (T2). We applied an integrative clustering approach to characterize both the group and individual responses to tDCS, as well as identifying naturally occurring subgroups that may be present within the total sample. Anodal tDCS failed to improve working memory performance in the total sample. Cluster analysis identified a subgroup of ‘responders’ who significantly improved their performance after anodal (vs. sham) stimulation, although not to a greater extent than the best baseline or sham condition. The proportion of ‘responders’ ranged from 15% to 59% across task conditions and behavioral outputs. Our findings show a high inter-individual variability of the tDCS response, suggesting that the use of tCDS may not be an effective tool to improve working memory performance in healthy subjects. We propose that the use of clustering methods is more suitable in identifying ‘responders’ and for evaluating the efficacy of this technique.

Response variability has been identified as a useful predictor of executive function and performance in non-clinical samples in the Go/NoGo task. The present study explores the utility of reaction time variability (RTV) and EEG measures as predictors of Go/NoGo performance outcomes and ERP component amplitudes. Forty-four young adults had EEG recorded across eyes-closed (EC) and eyes-open (EO) resting states, and during an auditory Go/NoGo task. The 18 individuals with the lowest/highest RTV were assessed for differences in behavioural outcomes. As expected, individuals with high RTV committed more Go/NoGo errors and had smaller Go P3b and NoGo P3a amplitudes, and greater Go Slow Wave positivity, reflecting inefficient decision-making and response control efforts underlying performance. When RTV and EEG measures were modelled as predictors of Go/NoGo responses, RTV and task-related changes in delta were identified as positive predictors of Go SW amplitude; while RTV and prestimulus delta amplitudes negatively predicted NoGo accuracy rates. Prestimulus delta was also found to solely predict Go mean RT and NoGo SW negativity; effects that were independent of RTV. As delta has been implicated in attention-related mechanisms, these findings suggest that inadequate attention and task engagement underpin the variability in Go/NoGo performance.

A lag schedule of reinforcement is one way to increase response variability; however, previous research has been mixed with regard to the necessary parameters to increase variability. For some individuals, low schedule requirements (e.g., Lag 1) are sufficient to increase variability. For other individuals, higher lag schedules (e.g., Lag 3) or a lag schedule in combination with prompting is needed to increase variability. We evaluated the efficiency of different within-session progressive lag schedules to increase response variability with 2 children with autism. Results showed that increasing the lag criterion across sessions increased variability to levels similar to beginning with a high lag schedule for one participant. When lag schedules did not increase variability for the second participant, we compared a variety of prompting procedures. Results of the prompting evaluation showed that a tact-priming procedure was effective to increase varied responding. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40616-018-0102-5) contains supplementary material, which is available to authorized users.

Studies with rats and pigeons showed that reinforcement of response variability improved learning of difficult response sequences. The results suggested that concurrent reinforcement of variability might be a helpful tool when educators or therapists attempt to teach individuals with learning difficulties. However, similar experiments with humans failed to confirm the results. In fact, in the human case, concurrent reinforcement of variability interfered with learning. The present experiment studied the same phenomenon with human participants in the context of a computer-based game. Our results were consistent with the nonhuman animal findings. When students in our experiment were concurrently reinforced for sequence variability, they were more likely than control participants to learn a difficult response sequence. We conclude that reinforcement of variability can facilitate learning-in humans as well as animals -and discuss possible reasons for the difference between our results and the previous human findings.

Augmentative and alternative communication (AAC) is a tool used by individuals unable to communicate or experience difficulty communicating vocally. Previous research has demonstrated that individuals will vary their communicative responding when reinforcement is delayed and when the response effort to communicate is increased. This study evaluated the effect of adjusting these variables to alter responding of three elementary age individuals with autism spectrum disorder who used AAC. A reversal design allowed for an evaluation of a functional relation between delay to reinforcement, response effort, and communication response allocation. When these parameters were changed, two participants shifted their responding while the third participant maintained his response allocation. This research provides further evidence that altering delay to reinforcement and response effort may aid in moving an individual from an AAC to spoken language. The researchers discuss outcomes in terms of how these variables can be manipulated in practice and the potential for altering other parameters of reinforcement in context of communication training.

Belief in free will is considered to be vital for human self-control, but most findings were obtained under externally constrained tasks. We investigated whether and how belief in free will contributes to self-control in a self-generating manner. Participants completed the Free Will and Determinism Scale in Japanese, and then performed a reversal learning task. During the task, participants' sympathetic activity was measured by finger plethysmography. We analyzed the relationships among belief in free will, sympathetic activity, and response variability indexed by entropy. The results revealed that belief in free will was positively related to sympathetic arousal when the contingencies of options and reward probabilities changed. In addition, this sympathetic arousal was positively related to increase in response variability. These results indicate that belief in free will contributes to the monitoring subprocess of self-control. We discuss the function of belief in free will and the mechanism of self-control.

Children with autism spectrum disorder and other developmental disabilities often exhibit invariant responding (i.e., restricted behavioral repertoires), deficits in communication, and challenging behavior. Approaches demonstrated in the basic and applied literature to increase response variability include extinction, lag schedules of reinforcement, and percentile schedules of reinforcement. Results of basic studies have also indicated that delays to reinforcement often produce increases in response variability. The purpose of the current study was to evaluate the effects of a delay to reinforcement on the variability of communication responses during functional communication training with individuals with developmental disabilities and histories of engaging in challenging behavior. Results indicated that delays to reinforcement increased mand variability with all four participants with variable effects on challenging behavior across participants.

The metronome response task (MRT)-a sustained-attention task that requires participants to produce a response in synchrony with an audible metronome-was recently developed to index response variability in the context of studies on mind wandering. In the present studies, we report on the development and validation of a visual version of the MRT (the visual metronome response task; vMRT), which uses the rhythmic presentation of visual, rather than auditory, stimuli. Participants completed the vMRT (Studies 1 and 2) and the original (auditory-based) MRT (Study 2) while also responding to intermittent thought probes asking them to report the depth of their mind wandering. The results showed that (1) individual differences in response variability during the vMRT are highly reliable; (2) prior to thought probes, response variability increases with increasing depth of mind wandering; (3) response variability is highly consistent between the vMRT and the original MRT; and (4) both response variability and depth of mind wandering increase with increasing time on task. Our results indicate that the original MRT findings are consistent across the visual and auditory modalities, and that the response variability measured in both tasks indexes a non-modality-specific tendency toward behavioral variability. The vMRT will be useful in the place of the MRT in experimental contexts in which researchers' designs require a visual-based primary task.

The ability to estimate proportions informs our immediate impressions of social environments (e.g., of the diversity of races or genders within a crowded room). This study examines how the distribution of attention during brief glances shapes estimates of group gender proportions. Performance-wise, subjects exhibit a canonical pattern of judgment errors: small proportions are overestimated while large values are underestimated. Subjects' eye movements at sub-second timescales reveal that these biases follow from a tendency to visually oversample members of the gender minority. Rates of oversampling dovetail with average levels of error magnitudes, response variability, and response times. Visual biases are thus associated with the inherent difficulty in estimating particular proportions. All results are replicated at a within-subjects level with non-human ensembles using natural scene stimuli; the observed attentional patterns and judgment biases are thus not exclusively guided by face-specific visual properties. Our results reveal the biased distribution of attention underlying typical judgment errors of group proportions.

Evidence exists about the influence of interoception on time-keeping functions. In the current study we further addressed this topic by testing the effect of fasting and snack on the ability to estimate the duration of reinforcement-oriented grasping actions. We found that, after fasting, the time estimation for the grasping of a primary reinforcement (i.e., a muffin) was positively influenced by moderate hunger. By contrast, high hunger after fasting interfered with the timing estimation for the grasping of a neutral object (i.e., a notepad). We also reported that, after snack, individuals with high residual levels of hunger showed higher variability of responses for the timing of primary-reinforcement-oriented actions; conversely, those with low level of hunger (after snack) showed higher response variability in the timing of secondary-reinforcement-oriented actions. Finally, timing variability in the fasting condition negatively correlated with the Body Mass Index of our participants. Overall, our results indicate that both the modification of the physiological state and individual traits related to appetite might affect the subjective experience of time. This is in line with the accumulating evidence documenting the influence of interoception in temporal processing and, more in general, with the New Look in Perception theoretical view, stating that the perception of external events might be influenced by motivational states.

Cortical sensory responses are highly variable across stimulus presentations. This variability can be correlated across neurons (due to some combination of dense intracortical connectivity, cortical activity level, and cortical state), with fundamental implications for population coding. Yet the interpretation of correlated response variability (or "noise correlation") has remained fraught with difficulty, in part because of the restriction to extracellular neuronal spike recordings. Here, we measured response variability and its correlation at the most microscopic level of electrical neural activity, the membrane potential, by obtaining dual whole cell recordings from pairs of cortical pyramidal neurons during visual processing in the turtle whole brain ex vivo preparation. We found that during visual stimulation, correlated variability adapts toward an intermediate level and that this correlation dynamic is likely mediated by intracortical mechanisms. A model network with external inputs, synaptic depression, and structure reproduced the observed dynamics of correlated variability. These results suggest that intracortical adaptation self-organizes cortical circuits toward a balanced regime at which correlated variability is maintained at an intermediate level.

Background It is well known that transcranial direct current stimulation (tDCS) is capable of modulating corticomotor excitability. However, a source of growing concern has been the observed inter- and intra-individual variability of tDCS-responses. Recent studies have assessed whether individuals respond in a predictable manner across repeated sessions of anodal tDCS (atDCS). The findings of these investigations have been inconsistent, and their methods have some limitations (i.e. lack of sham condition or testing only one tDCS intensity). Objective To study inter- and intra-individual variability of atDCS effects at two different intensities on primary motor cortex (M1) excitability. Methods Twelve subjects participated in a crossover study testing 7-min atDCS over M1 in three separate conditions (2 mA, 1 mA, sham) each repeated three times separated by 48 h. Motor evoked potentials were recorded before and after stimulation (up to 30min). Time of testing was maintained consistent within participants. To estimate the reliability of tDCS effects across sessions, we calculated the Intra-class Correlation Coefficient (ICC). Results AtDCS at 2 mA, but not 1 mA, significantly increased cortical excitability at the group level in all sessions. The overall ICC revealed fair to high reliability of tDCS effects for multiple sessions. Given that the distribution of responses showed important variability in the sham condition, we established a Sham Variability-Based Threshold to classify responses and to track individual changes across sessions. Using this threshold an intra-individual consistent response pattern was then observed only for the 2 mA condition. Conclusion 2 mA anodal tDCS results in consistent intra- and inter-individual increases of M1 excitability.

This study examined relations between multiple measures of maternal iron status assessed 3 months post-partum, and infant processing speed (longest look during visual habituation), memory (novelty preference), attention (heart rate changes), and neural response variability (in auditory event-related potentials) at 3 and 9 months. Plasma iron was associated with 9-month novelty preference and longest look, and developmental changes in longest look. Hemoglobin predicted sustained attention, and both plasma iron and soluble transferrin receptors predicted neural response variability at 9 months. Improved maternal iron appears to have a positive impact on infant cognitive development even in a well-nourished, low-risk sample.

We evaluated the effects of lag schedules of reinforcement during functional communication training (FCT) on the varied use of mands and challenging behavior by two individuals diagnosed with autism. Specifically, we compared the effects of Lag 0 and Lag 1 schedules of reinforcement during FCT. The results showed that each participant exhibited increases in varied mand responding during FCT with the Lag 1 schedule of reinforcement relative to Lag 0; challenging behavior remained low during both FCT lag conditions relative to baseline. Results are discussed in terms of treatment implications relating to FCT and the potential prevention and/or mitigation of clinical relapse during challenges to treatment.

Background Reduction or differences in facial expression are a core diagnostic feature of autism spectrum disorder (ASD), yet evidence regarding the extent of this discrepancy is limited and inconsistent. Use of automated facial expression detection technology enables accurate and efficient tracking of facial expressions that has potential to identify individual response differences. Methods Children and adults with ASD (N = 124) and typically developing (TD, N = 41) were shown short clips of “funny videos.” Using automated facial analysis software, we investigated differences between ASD and TD groups and within the ASD group in evidence of facial action unit (AU) activation related to the expression of positive facial expression, in particular, a smile. Results Individuals with ASD on average showed less evidence of facial AUs (AU12, AU6) relating to positive facial expression, compared to the TD group (p < .05, r = − 0.17). Using Gaussian mixture model for clustering, we identified two distinct distributions within the ASD group, which were then compared to the TD group. One subgroup (n = 35), termed “over-responsive,” expressed more intense positive facial expressions in response to the videos than the TD group (p < .001, r = 0.31). The second subgroup (n = 89), (“under-responsive”), displayed fewer, less intense positive facial expressions in response to videos than the TD group (p < .001; r = − 0.36). The over-responsive subgroup differed from the under-responsive subgroup in age and caregiver-reported impulsivity (p < .05, r = 0.21). Reduced expression in the under-responsive, but not the over-responsive group, was related to caregiver-reported social withdrawal (p < .01, r = − 0.3). Limitations This exploratory study does not account for multiple comparisons, and future work will have to ascertain the strength and reproducibility of all results. Reduced displays of positive facial expressions do not mean individuals with ASD do not experience positive emotions. Conclusions Individuals with ASD differed from the TD group in their facial expressions of positive emotion in response to “funny videos.” Identification of subgroups based on response may help in parsing heterogeneity in ASD and enable targeting of treatment based on subtypes. Trial registration ClinicalTrials.gov, NCT02299700. Registration date: November 24, 2014

Individuals with autism spectrum disorder (ASD) are often reported to exhibit an apparent indifference to pain or temperature. Leading models suggest that this behavior is the result of elevated perceptual thresholds for thermal stimuli, but data to support these assertions are inconclusive. An alternative proposal suggests that the sensory features of ASD arise from increased intra-individual perceptual variability. In this study, we measured method-of-limits warm and cool detection thresholds in 142 individuals (83 with ASD, 59 with typical development [TD], aged 7–54 years), testing relationships with diagnostic group, demographics, and clinical measures. We also investigated the relationship between detection thresholds and a novel measure of intra-individual (trial-to-trial) threshold variability, a putative index of “perceptual noise.” This investigation found no differences in thermal detection thresholds between individuals with ASD and typical controls, despite large differences between groups in sensory reactivity questionnaires and modest group differences in intra-individual variability. Lower performance IQ, male sex, and higher intra-individual variability in threshold estimates were the most significant predictors of elevated detection thresholds. Although no psychophysical measure was significantly correlated with questionnaire measures of sensory hyporeactivity, large intra-individual variability may partially explain the elevated psychophysical thresholds seen in a subset of the ASD population.

Simple Summary The Cat/Dog–Owner Relationship Scale (C/DORS) is a questionnaire aimed to assess specific aspects of the pet–owner relationship. While the entire scale can be administered to both dog and cat owners, its validity and reliability have never been tested on dogs. Furthermore, validity and reliability of a scale may change depending on the respondents’ language and cultural background. Since the C/DORS was developed in English, we aimed to translate it into Italian and assess its validity and reliability on a sample of Italian dog owners. The response scale was modified to improve the variability of the owners’ responses. Overall, validity and reliability were good. The scale had the same three-factor structure (Perceived Emotional Closeness = PEC, Pet–Owner Interactions = POI, Perceived Costs = PC) reported for the original English version, although some items were removed because they did not fit the statistical model. The PEC subscale had the highest correlations with the subscales of the Lexington Attachment to Pets Scale. Finally, being a student owner was associated with higher PEC and POI scores. Conversely, owning a dog with behavioural problems was associated with lower PEC and higher PC. Owners whose dogs lived outdoors reported lower POI. Pet dog owners reported higher PEC than AAI dog owners. Abstract The Cat/Dog–Owner Relationship Scale (C/DORS) can be administered to both dog and cat owners. However, the scale as a whole has never been validated on a sample of dog owners. Furthermore, it has never been translated into Italian. The aim of this study was to translate the C/DORS into Italian, modify its response scale in order to improve the degree of response variability, and test its validity and reliability on a sample of dog-owners. Exploratory factor analysis revealed the same three-factor structure (Perceived Emotional Closeness = PEC, Pet–Owner Interactions = POI, Perceived Costs = PC) as the original English version, although some items had to be removed because of low- or cross-loadings. The validity of the construct was confirmed by confirmatory factor analysis, by the correlations between each of the subscales and the C/DORS total score, and by the correlations with the Lexington Attachment to Pets Scale. Cronbach’s α values for each subscale were above acceptable levels. Student owners scored higher on PEC and POI than owners with other occupations. Owners of dogs with behavioural problems scored lower on PEC and higher on PC. Keeping the dog outdoor was associated with lower POI. Finally, pet dog owners scored higher on PEC than AAI dog owners.

Non-invasive brain stimulation (NIBS) is proving to be an effective method to enhance cognitive skills and motor coordination, which makes it a precious tool both in the intellectual sphere and in sports. Accordingly, in selective-competitive contexts, the use of NIBS can threaten the fairness and produce unexpected social composition effects. To avoid those negative consequences, it might be recommended that people should declare the use of enhancers of any kind, including those that are not explicitly prohibited. But the duty of disclosure seems particularly problematic to be enforced with NIBS, as it is not currently detectable. Moreover, considering the fact that NIBS has very different enhancement effects on each individual, all these elements may create strong performance inequalities and consequent discrimination, if NIBS were to become widespread. In this paper, within a Rawlsian theoretical framework, we highlight the risks posed by this new performance-enhancing technology and we propose compelling moral reasons for some forms of regulation of non-clinical use of NIBS.

Surveys are one of the most popular ways to collect employee information. Because of their widespread use, data quality is an increasingly important concern. The purpose of this paper is to (1) introduce the intra-individual response variability (IRV) index as an easily calculated and flexible way to detect insufficient effort responding (IER); (2) examine the extent to which various IER indices detect the same or different respondents engaging in IER behavior; and (3) investigate relationships between individual differences and commonly used IER indices to better understand systematic and theoretically relevant IER behavior. In a two-part study, 199 undergraduates responded to questionnaires online, and various IER indices were calculated. The IRV index identifies different respondents than other IER indices. Values on the IRV index (as well as other IER indices) are related to scores on theoretically meaningful individual differences in conscientiousness, agreeableness, and boredom proneness. This study provides researchers with a robust, easily calculated, and flexible means for screening questionnaire data for IER behavior. Practical recommendations for finding and making decisions about IER behavior patterns are provided. This study introduces the IRV index, an extension of the long string, used to identify survey research participants who likely engaged in one type of IER behavior. It is also one of the first studies to evaluate the extent to which IER indices identify different respondents as having engaged in IER and provides additional evidence that values on these indices are related to individual differences.

The detection of a sensory stimulus arises from a significant change in neural activity, but a sensory neuron's response is rarely identical to successive presentations of the same stimulus. Large trial-to-trial variability would limit the central nervous system's ability to reliably detect a stimulus, presumably affecting perceptual performance. However, if response variability were to decrease while firing rate remained constant, then neural sensitivity could improve. Here, we asked whether engagement in an auditory detection task can modulate response variability, thereby increasing neural sensitivity. We recorded telemetrically from the core auditory cortex of gerbils, both while they engaged in an amplitude-modulation detection task and while they sat quietly listening to the identical stimuli. Using a signal detection theory framework, we found that neural sensitivity was improved during task performance, and this improvement was closely associated with a decrease in response variability. Moreover, units with the greatest change in response variability had absolute neural thresholds most closely aligned with simultaneously measured perceptual thresholds. Our findings suggest that the limitations imposed by response variability diminish during task performance, thereby improving the sensitivity of neural encoding and potentially leading to better perceptual sensitivity.SIGNIFICANCE STATEMENTThe detection of a sensory stimulus arises from a significant change in neural activity. However, trial-to-trial variability of the neural response may limit perceptual performance. If the neural response to a stimulus is quite variable, then the response on a given trial could be confused with the pattern of neural activity generated when the stimulus is absent. Therefore, a neural mechanism that served to reduce response variability would allow for better stimulus detection. By recording from the cortex of freely moving animals engaged in an auditory detection task, we found that variability of the neural response becomes smaller during task performance, thereby improving neural detection thresholds.

Adolescence is a period of learning, exploration, and continuous adaptation to fluctuating environments. Response variability during adolescence is an important, understudied, and developmentally appropriate behavior. The purpose of this study was to identify the association between performance on a dynamic risky decision making task and white matter microstructure in a sample of 48 adolescents (14-16 years). Individuals with the greatest response variability on the task obtained the widest range of experience with potential outcomes to risky choice. When compared with their more behaviorally consistent peers, adolescents with greater response variability rated real-world examples of risk taking behaviors as less risky via self-report. Tract-Based Spatial Statistics (TBSS) were used to examine fractional anisotropy (FA) and mean diffusivity (MD). Greater FA in long-range, late-maturing tracts was associated with higher response variability. Greater FA and lower MD were associated with lower riskiness ratings of real-world risky behaviors. Results suggest that response variability and lower perceived risk attitudes of real-world risk are supported by neural maturation in adolescents.

Objective This article examines the distinction between group-based issue opinion formation (what we term “following the crowd”) and idiosyncratic or nongroup-based formation (what we term “thinking outside of the box”). The argument put forth is that issue saliency can lead citizens to think about issues in nongroup-based terms. Method We use heteroskedastic regression to measure the degree to which group-based variables explain issue opinions. Using group variables (demographics, party identification, etc.) to estimate respondents' issue responses means that nongroup variation is soaked up by the error term. Results We find that citizens who view an issue as highly salient are more likely to “think outside the box,” while citizens who view an issue as less salient are more likely to “follow the crowd” by defaulting to their group memberships and identifications. Conclusion Our results indicate that response variability (less consistency within groups) on issue opinions is not always the result of uncertain citizens, nonattitudes, or measurement error. In some situations, greater response variability can reflect a deliberative and policy-based form of opinion formation.

University students partitioned in four groups were treated to a four-phase resurgence preparation in which three response sequences were sequentially acquired in the first three phases and tested for serial positioning effects and response variability in terminal resurgence phase. For the three test groups, three colored backgrounds served as the contextual stimuli that corresponded to the acquisition of the response sequences in the initial three phases. In the final resurgence phase, all response sequences were placed on extinction. The three test groups were re-presented a respective colored background found in one of the earlier acquisition phases. The fourth group did not involve any colored background throughout the entire experiment. Across all three test groups, the highest acquired response sequence proportion was correlated with the discriminative stimulus present in the resurgence phase. The no-color group without contextual change across phases showed recency and primacy effects consistent with those found in serial position studies. Moreover, the presence of the discriminative stimulus in the resurgence phase resulted in less variable response sequences relative to the no-color group. These findings support the role of discriminative stimuli in the manner with which response patterns are organized in resurgence.

Undetected carelessly given responses in survey data diminish the credibility of study findings. We therefore examined two pressing issues: the accuracy of popular screening indices, and the impact of careless responding on the psychometric properties of constructs. In an experiment in Study 1, induced response sets were used to examine the effectiveness of seven indices in detecting careless responding. Response time per item, personal reliability, psychometric synonyms, psychometric antonyms, and Mahalanobis distance were effective. However, the longstring and intra-individual response variability were ineffective. In Study 2, the effects of careless responding were examined under normal study conditions. In this sample, 33% of the participants were identified as careless responders. Careless responding inflated item variances, biased item means towards the scale midpoint, increased residual variances of construct indicators, and reduced the within-group agreement on consensus-based constructs. To enhance the credibility of findings, therefore, screenings for careless responding should be applied regularly.

To determine the neuroelectric underpinnings of exercise-induced changes in working memory, this study investigated the acute effects ofaerobic exercise (AE) on the P3 component of an event-related potential and brain oscillations during a serial n-back task. Task-related electroencephalography was collected in 23 young adults following 20 min of rest and AE on separate, counterbalanced days. The results revealed reductions in standard deviation of response time and coefficient of variation of response time following AE compared to rest. Neuroelectric analyses showed increased P3 amplitude following AE compared to rest. Task-related frontal alpha desynchronization was stronger in the 2-back compared with the 1-back task following AE, while no such modulation was observed following rest. These findings suggest AE may temporarily enhance working memory, as reflected by decreases in response variability, which are accompanied by neuroelectric indices reflecting greater upregulation of attentional processes.