Between-subject Variance Research Articles

Grammatical taboos

Abstract This explorative study focuses on grammatical taboos in German, morphosyntactic constructions which are subject to stigmatisation, as they regularly occur in standard languages. They are subjected to systematic experimental testing in a questionnaire study with gradient rating scales on two salient and two non-salient grammatical taboo phenomena of German. The study is divided into three subexperiments with different judgement types, an aesthetic judgement, a norm-oriented judgement and the sort of possibility judgement that comes closest to linguists’ understanding of grammar. Included in the investigated material are also examples of ordinary gradient grammaticality: unmarked, marked and ungrammatical sentences. The empirical characteristics of grammatical taboos are compared to those ordinary cases with the finding that they are rated at the level of markedness, but differ from ordinary markedness in that they produce a different pattern of between-subject variance. In addition, we find that grammatical taboos have a particular disadvantage under the aesthetic judgement type. The paper also introduces the concept of empirical grammaticality as a necessary theoretical cornerstone for empirical linguistics. Methodically, the study applies a mix of parametric and non-parametric methods of statistical analysis.

Determinants of pulse wave velocity trajectories from youth to young adulthood: the Georgia Stress and Heart Study.

Increased arterial stiffness measured by pulse wave velocity (PWV) has been shown to be an important parameter of cardiovascular risk. Longitudinal development of PWV from youth to early adulthood and its possible sociodemographic, anthropometric, hemodynamic and behavioral moderators will be illustrated. Individual growth curves of carotid-distal PWV across age were created for 559 African American and European American men and women with a maximum of five assessments over an average of 7-year follow-up (mean age at participants' first assessment, 22.3 ± 3.4). African Americans and men had significantly higher PWV than did European Americans and women (Ps < 0.01), respectively. A three-way interaction (P < 0.001) between age, sex and ethnicity was observed with African American men displaying a larger rate of increase in PWV with age than the other three ethnic and sex groups. The ethnicity and sex effects on PWV persisted when controlling for other moderators. Waist circumference was the strongest anthropometric predictor but its effect on PWV was only significant in women. Mean arterial pressure was the strongest hemodynamic predictor, marital status of parents was the strongest socioeconomic predictor and marijuana use was the strongest behavioral predictor of PWV. The best-fitting full model explained in total 59.4% of the between-subject variance in PWV with ethnicity, sex and age explaining 25.6%. We observed significant ethnic and sex differences in longitudinal trajectories of PWV in youth and young adults. In addition, individual differences in PWV growth can largely be explained by mean arterial pressure, waist, marital status of parents and marijuana use.

Multilevel analysis of matching behavior.

Multilevel modeling has been considered a promising statistical tool in the field of the experimental analysis of behavior and may serve as a convenient statistical analysis for matching behavior because it structures data in groups (or levels) to account simultaneously for the within-subject and between-subject variances. Heretofore, researchers have sometimes pooled data erroneously from different subjects in a single analysis by using average ratios, average response and reinforcer rates, aggregation of subjects, etc. Unfortunately, this leads to loss of information and biased estimations, which can severely undermine generalization of the results. Instead, a multilevel approach is advocated to combine several subjects' matching behavior. A reanalysis of previous data on matching behavior is provided to illustrate the method and point out its advantages. It illustrates that multilevel regression leads to better estimations, is more convenient, and offers more behavioral information. We hope this paper will encourage the use of multilevel modeling in the statistical practices of behavior analysts.

Sex-specific contribution of DHEA-cortisol ratio to prefrontal-hippocampal structural development, cognitive abilities and personality traits.

Although dehydroepiandrosterone (DHEA) may exert neuroprotective effects in the developing brain, prolonged or excessive elevations in cortisol may exert neurotoxic effects. The ratio between DHEA and cortisol (DC ratio) has been linked to internalising and externalising disorders, as well as cognitive performance, supporting the clinical relevance of this hormonal ratio during development. However, the brain mechanisms by which these effects may be mediated have not yet been identified. Furthermore, although there is evidence that the effects of cortisol in the central nervous system may be sexually dimorphic in humans, the opposite is true for DHEA, with human studies showing no sex-specific associations in cortical thickness, cortico-amygdalar or cortico-hippocampal structural covariance. Therefore, it remains unclear whether sex moderates the developmental associations between DC ratio, brain structure, cognition and behaviour. In the present study, we examined the associations between DC ratio, structural covariance of the hippocampus with whole-brain cortical thickness, and measures of personality, behaviour and cognition in a longitudinal sample of typically developing children, adolescents and young adults aged 6-22years (N=225 participants [F=128]; 355 scans [F=208]), using mixed effects models that accounted for both within- and between-subject variances. We found sex-specific interactions between DC ratio and anterior cingulate cortex-hippocampal structural covariance, with higher DC ratios being associated with a more negative covariance between these structures in girls, and a more positive covariance in boys. Furthermore, the negative prefrontal-hippocampal structural covariance found in girls was associated with higher verbal memory and mathematical ability, whereas the positive covariance found in boys was associated with lower cooperativeness and reward dependence personality traits. These findings support the notion that the ratio between DHEA and cortisol levels may contribute, at least in part, to the development of sex differences in cognitive abilities, as well as risk for internalising/externalising disorders, via an alteration in prefrontal-hippocampal structure during the transition from childhood to adulthood.

Working memory performance in the elderly relates to theta-alpha oscillations and is predicted by parahippocampal and striatal integrity

The ability to maintain information for a short period of time (i.e. working memory, WM) tends to decrease across the life span with large inter-individual variability; the underlying neuronal bases, however, remain unclear. To address this issue, we used a multimodal imaging approach (voxel-based morphometry, diffusion-tensor imaging, electroencephalography) to test the contribution of brain structures and neural oscillations in an elderly population. Thirty-one healthy elderly participants performed a change-detection task with different load conditions. As expected, accuracy decreased with increasing WM load, reflected by power modulations in the theta-alpha band (5–12 Hz). Importantly, these power changes were directly related to the tract strength between parahippocampus and parietal cortex. Furthermore, between-subject variance in gray matter volume of the parahippocampus and dorsal striatum predicted WM accuracy. Together, our findings provide new evidence that WM performance critically depends on parahippocampal and striatal integrity, while theta-alpha oscillations may provide a mechanism to bind the nodes within the WM network.

Listener Factors Explain Little Variability in Self-Adjusted Hearing Aid Gain.

Self-adjustment of hearing aid gain can provide valuable information about the gain preferences of individual listeners, but these preferences are not well understood. Listeners with mild-to-moderate hearing loss used self-adjustment to select amplification gain and compression parameters in real time on a portable touch screen device while listening in quiet and noisy backgrounds. Adjustments to gain prescribed by the National Acoustics Laboratories' non-linear fitting procedure (NAL-NL2) showed large between-subject variability. Known listener characteristics (age, gender, hearing thresholds, hearing aid experience, acceptable noise level, and external ear characteristics) and listener engagement with the self-adjustment software were examined as potential predictors of this variability. Neither listener characteristics nor time spent adjusting gain were robust predictors of gain change from NAL-NL2. Listeners with less than 2 years of hearing aid experience and who also had better hearing thresholds tended to select less gain, relative to NAL-NL2, than experienced hearing aid users who had poorer thresholds. Listener factors explained no more than 10% of the between-subject variance in deviation from NAL-NL2, suggesting that modifying prescriptive fitting formulae based on the factors examined here would be unlikely to result in amplification parameters that are similar to user-customized settings. Self-adjustment typically took less than 3 min, indicating that listeners could use comparable technology without a substantial time commitment.

A better (Bayesian) interval estimate for within-subject designs

We develop a Bayesian highest-density interval (HDI) for use in within-subject designs. This credible interval is based on a standard noninformative Jeffreys prior and a modified posterior distribution that conditions on both the data and point estimates of the subject-specific random effects. Conditioning on the estimated random effects removes between-subject variance and produces intervals that are the Bayesian analogue of the within-subject confidence interval proposed in Loftus and Masson (1994). We show that the latter interval can also be derived as a Bayesian within-subject HDI under a certain improper prior. We argue that the proposed new interval is superior to the original within-subject confidence interval, on the grounds of (a) it being based on a more sensible prior, (b) it having a clear and intuitively appealing interpretation, and (c) because its length is always smaller. A generalization of the new interval that can be applied to heteroscedastic data is also derived, and we show that the resulting interval is numerically equivalent to the standardization method discussed in Franz and Loftus (2012); however, our work provides a Bayesian formulation for the standardization method, and in doing so we identify the associated prior distribution.

Modeling Intraindividual Variability in Three-Level Multilevel Models

Abstract. The mixed-effects location scale model is an extension of a multilevel model for longitudinal data. It allows covariates to affect both the within-subject variance and the between-subject variance (i.e., the intercept variance) beyond their influence on the means. Typically, the model is applied to two-level data (e.g., the repeated measurements of persons), although researchers are often faced with three-level data (e.g., the repeated measurements of persons within specific situations). Here, we describe an extension of the two-level mixed-effects location scale model to such three-level data. Furthermore, we show how the suggested model can be estimated with Bayesian software, and we present the results of a small simulation study that was conducted to investigate the statistical properties of the suggested approach. Finally, we illustrate the approach by presenting an example from a psychological study that employed ecological momentary assessment.

Mixed Model Analysis of Between-Subject Variability in Overnight Corneal Swelling and Deswelling With Silicone Hydrogel Lenses.

To model between subject variability of corneal swelling (CS) and deswelling after overnight wear of silicone hydrogel (SiHy) contact lenses. A total of 29 neophyte subjects wore 12 SiHy lenses with central transmissibility range of 31 to 211 Dk/t units on separate nights, in random order, and on one eye only. The contralateral eye served as the control. Central corneal thickness was measured using digital optical pachymetry before lens insertion, immediately after lens removal on waking, then 20, 40 minutes, 1, 2, and 3 hours later. Mixed modelling was conducted for simultaneous analysis of group and between-subject effects of CS and deswelling. The best model for overnight CS versus Dk/t was linear with a random intercept showing constant between-subject differences in CS for different Dk/t values. The best fit for corneal deswelling versus time was a curvilinear random intercept and random slope model. About 90% of the total between-subject deswelling variance in either lens or control eyes was due to the intercept variability with much less (∼10%) being due to the variability of the individual deswelling rate (slope). Subject age, sex, and ametropia were not predictors of individual corneal swelling in the swelling versus Dk/t analysis. Age, however, was a significant (inverse) predictor of the rate of corneal deswelling, only in lens-wearing eyes. A large proportion of variability in corneal swelling is because of subject-specific differences in corneal response to hypoxia. This shows that "low swellers" and "high swellers" actually do exist.

Prolonged Reduction in Shoulder Strength after Transcutaneous Electrical Nerve Stimulation Treatment of Exercise‐Induced Acute Muscle Pain

Transcutaneous electrical nerve stimulation (TENS) is commonly used for reducing musculoskeletal pain to improve function. However, peripheral nerve stimulation using TENS can alter muscle motor output. Few studies examine motor outcomes following TENS in a human pain model. Therefore, this study investigated the influence of TENS sensory stimulation primarily on motor output (strength) and secondarily on pain and disability following exercise-induced delayed-onset muscle soreness (DOMS). Thirty-six participants were randomized to a TENS treatment, TENS placebo, or control group after completing a standardized DOMS protocol. Measures included shoulder strength, pain, mechanical pain sensitivity, and disability. TENS treatment and TENS placebo groups received 90minutes of active or sham treatment 24, 48, and 72hours post-DOMS. All participants were assessed daily. A repeated measures analysis of variance and post-hoc analysis indicated that, compared to the control group, strength remained reduced in the TENS treatment group (48hours post-DOMS, P<0.05) and TENS placebo group (48hours post-DOMS, P<0.05; 72hours post-DOMS, P<0.05). A mixed-linear modeling analysis was conducted to examine the strength (motor) change. Randomization group explained 5.6% of between-subject strength variance (P<0.05). Independent of randomization group, pain explained 8.9% of within-subject strength variance and disability explained 3.3% of between-subject strength variance (both P<0.05). While active and placebo TENS resulted in prolonged strength inhibition, the results were nonsignificant for pain. Results indicated that higher pain and higher disability were independently related to decreased strength. Regardless of the impact on pain, TENS, or even the perception of TENS, may act as a nocebo for motor output.

Abstract P204: Growth and Moderators of Pulse Wave Velocity From Childhood to Adulthood

Background: Increased arterial stiffness measured by pulse wave velocity (PWV) has been shown to be an important parameter in the assessment of cardiovascular risk. However little is known about its longitudinal development from childhood to adulthood and its possible sociodemographic, anthropometric, hemodynamic and behavioral moderators. Methods and Results: Individual growth curves of carotid-distal PWV across age were created for 559 African American and European American males and females with a maximum of 5 assessments over a 13-year period (age, 13.7-37.3). African Americans and males had significantly higher PWV than did European Americans and females (Ps&lt;0.01), respectively. A 3-way interaction (P&lt;0.01) between age, gender and ethnicity was observed with African American males displaying a larger rate of increase in PWV with age than the other 3 ethnic and gender groups. The ethnicity and gender effects on PWV persisted when controlling for other moderators. Waist circumstance was the strongest anthropometric predictor but its effect on PWV was only significant in females. Mean arterial pressure was the strongest hemodynamic predictor, marital status of parents was the strongest socioeconomic predictor, and illegal drug use was the strongest behavioral predictor of PWV. The best-fitting full model explained in total 61.6% of the between-subject variance in PWVwith ethnicity, genderand age explaining25%. Conclusion: We observed significant ethnic and gender differences in longitudinal trajectories of PWV in youth and young adults. Apart from these ethnicity and gender effects, individual differences in PWV growth can largely be explained by mean arterial pressure, waist circumstance, marital status and illegal drug use.

Greater variability in daily physical activity is associated with poorer mental health profiles among obese adults

Research is inconclusive about whether physical activity (PA) should be performed every day or performed less frequently but in longer bouts to obtain mental health benefits. The current study examined the extent to which day-to-day variability in PA is associated with adults' mental health, and if this association differed by Body Mass Index (BMI). Adults (N = 116) completed three waves of data collection (each lasting 4 days) during which participants completed a questionnaire assessing mental health (life satisfaction, depressive symptoms, perceived stress), wore a waist accelerometer, and had height and weight measured. This study employed a novel two-stage data analysis approach using the standalone program MIXWILD. The first-stage model partitioned mean level as well as between-subject and within-subject variances in daily PA by estimating a random location (subject-level mean) and a random scale (subject-level variability) for daily PA. In the second-stage, these random subject effects for daily PA along with their interactions with BMI were used as predictors for subject-level mental health outcomes. Associations between subject-level variability in daily PA and mental health outcomes significantly differed depending on adults’ BMI (life satisfaction: β = −0.05, p < 0.05; depressive symptoms: β = 0.03, p < 0.05; perceived stress: β = 0.04, p < 0.01). Greater day-to-day variability in PA was associated with poorer mental health in adults with higher BMI values as compared to adults with lower BMI. For individuals with high BMI values, inconsistent activity patterns may have consequences that diminish mental health. Strategies that promote consistency in daily PA may be useful for individuals with high BMI to enhance mental health.

Reproducibility of Heart Rate Variability Is Parameter and Sleep Stage Dependent.

Objective: Measurements of heart rate variability (HRV) during sleep have become increasingly popular as sleep could provide an optimal state for HRV assessments. While sleep stages have been reported to affect HRV, the effect of sleep stages on the variance of HRV parameters were hardly investigated. We aimed to assess the variance of HRV parameters during the different sleep stages. Further, we tested the accuracy of an algorithm using HRV to identify a 5-min segment within an episode of slow wave sleep (SWS, deep sleep).Methods: Polysomnographic (PSG) sleep recordings of 3 nights of 15 healthy young males were analyzed. Sleep was scored according to conventional criteria. HRV parameters of consecutive 5-min segments were analyzed within the different sleep stages. The total variance of HRV parameters was partitioned into between-subjects variance, between-nights variance, and between-segments variance and compared between the different sleep stages. Intra-class correlation coefficients of all HRV parameters were calculated for all sleep stages. To identify an SWS segment based on HRV, Pearson correlation coefficients of consecutive R-R intervals (rRR) of moving 5-min windows (20-s steps). The linear trend was removed from the rRR time series and the first segment with rRR values 0.1 units below the mean rRR for at least 10 min was identified. A 5-min segment was placed in the middle of such an identified segment and the corresponding sleep stage was used to assess the accuracy of the algorithm.Results: Good reproducibility within and across nights was found for heart rate in all sleep stages and for high frequency (HF) power in SWS. Reproducibility of low frequency (LF) power and of LF/HF was poor in all sleep stages. Of all the 5-min segments selected based on HRV data, 87% were accurately located within SWS.Conclusions: SWS, a stable state that, in contrast to waking, is unaffected by internal and external factors, is a reproducible state that allows reliable determination of heart rate, and HF power, and can satisfactorily be detected based on R-R intervals, without the need of full PSG. Sleep may not be an optimal condition to assess LF power and LF/HF power ratio.

Stability of MRI metrics in the advanced research core of the NCAA-DoD concussion assessment, research and education (CARE) consortium.

The NCAA-DoD Concussion Assessment, Research, and Education (CARE) consortium is performing a large-scale, comprehensive study of sport related concussions in college student-athletes and military service academy cadets. The CARE "Advanced Research Core" (ARC), is focused on executing a cutting-edge investigative protocol on a subset of the overall CARE athlete population. Here, we present the details of the CARE ARC MRI acquisition and processing protocol along with preliminary analyzes of within-subject, between-site, and between-subject stability across a variety of MRI biomarkers. Two experimental datasets were utilized for this analysis. First, two "human phantom" subjects were imaged multiple times at each of the four CARE ARC imaging sites, which utilize equipment from two imaging vendors. Additionally, a control cohort of healthy athletes participating in non-contact sports were enrolled in the study at each CARE ARC site and imaged at four time points. Multiple morphological image contrasts were acquired in each MRI exam; along with quantitative diffusion, functional, perfusion, and relaxometry imaging metrics. As expected, the imaging markers were found to have varying levels of stability throughout the brain. Importantly, between-subject variance was generally found to be greater than within-subject and between-site variance. These results lend support to the expectation that cross-site and cross-vendor advanced quantitative MRI metrics can be utilized to improve analytic power in assessing sensitive neurological variations; such as those effects hypothesized to occur in sports-related-concussion. This stability analysis provides a crucial foundation for further work utilizing this expansive dataset, which will ultimately be freely available through the Federal Interagency Traumatic Brain Injury Research Informatics System.

Effect of sequence variants on variance in glucose levels predicts type 2 diabetes risk and accounts for heritability.

Sequence variants that affect mean fasting glucose levels do not necessarily affect risk for type 2 diabetes (T2D). We assessed the effects of 36 reported glucose-associated sequence variants on between- and within-subject variance in fasting glucose levels in 69,142 Icelanders. The variant in TCF7L2 that increases fasting glucose levels increases between-subject variance (5.7% per allele, P = 4.2 × 10-10), whereas variants in GCK and G6PC2 that increase fasting glucose levels decrease between-subject variance (7.5% per allele, P = 4.9 × 10-11 and 7.3% per allele, P = 7.5 × 10-18, respectively). Variants that increase mean and between-subject variance in fasting glucose levels tend to increase T2D risk, whereas those that increase the mean but reduce variance do not (r2 = 0.61). The variants that increase between-subject variance increase fasting glucose heritability estimates. Intuitively, our results show that increasing the mean and variance of glucose levels is more likely to cause pathologically high glucose levels than increase in the mean offset by a decrease in variance.

Behavioral Patterns and Associations with Glucose Control During 12-Week Randomized Free-Living Clinical Trial of Day and Night Hybrid Closed-Loop Insulin Delivery in Adults with Type 1 Diabetes.

Objectives: We evaluated patterns of meal intake, insulin bolus delivery, and fingerstick glucose measurements during hybrid closed-loop and sensor-augmented pump (SAP) therapy, including associations with glucose control.Methods: Data were retrospectively analyzed from pump-treated adults with type 1 diabetes who underwent, in random order, 12 weeks free-living closed-loop (n = 32) and 12 weeks SAP (n = 33) periods. We quantified daily patterns of main meals, snacks, prandial insulin boluses, correction boluses, and fingerstick glucose measurements by analyzing data recorded on the study glucometer and on study insulin pump.Results: We analyzed 1942 closed-loop days and 2530 SAP days. The total number of insulin boluses was reduced during closed-loop versus SAP periods by mean 1.0 per day (95% confidence interval 0.6–1.4, P < 0.001) mainly because of a reduced number of correction boluses by mean 0.7 per day (0.4–1.0, P < 0.001). Other behavioral patterns were unchanged. The carbohydrate content of snacks but not the number of snacks was positively correlated with (1) glycemic variability as measured by standard deviation of sensor glucose (closed-loop P < 0.05; SAP P < 0.01), (2) mean sensor glucose (P < 0.05), and (3) postintervention HbA1c (P < 0.05). Behavioral patterns explained 47% of between-subject variance in glucose variability during SAP period and 30%–33% of variance of means sensor glucose and postintervention HbA1c.Conclusion: Fewer correction boluses are delivered during closed-loop period. The size of snacks appears to worsen glucose control possibly because of carbohydrate-rich content of snacks. Modifiable behavioral patterns may be important determinants of glucose control.

A STUDY TO MODEL RATES OF CHANGE ON NEUROPSYCHOLOGICAL TEST MEASURES IN SUBJECTS DIAGNOSED WITH BEHAVIORAL VARIANT FRONTOTEMPORAL DEMENTIA AND HEALTHY SUBJECTS

Information about the sensitivity of cognitive tests to frontotemporal dementia (FTD) natural progression is limited and highly variable since neuropsychological assessments in FTD natural history studies are typically performed yearly, using tests optimized for clinical description and diagnosis (Knopman DS, et al. Brain 2008;131(Pt 11):2957–68; Ranasinghe KG, et al. Neurology 2016;86(7):600–10). This study goal is to identify cognitive measures predictive of behavioral variant FTD (bvFTD) progression over 12 months or less, to estimate this effect size and its clinical meaningfulness by examining their relationship with changes in behavioral, functional, quality of life (QOL), and caregiver burden measures. 70 subjects (40 with early-stages, symptomatic bvFTD with their caregivers and 30 healthy volunteers, matched by age and education) will be enrolled in this observational study conducted at 10 FTD centers within United States. Subjects will undergo cognitive tests during 13 monthly visits (quarterly at site, otherwise at home). Tests were selected for their previously demonstrated sensitivity to change over short intervals, relative lack of learning and cultural effect, breadth of cognitive domains relevant to bvFTD. Frequent assessments should increase sensitivity to decline (relative to annual assessments) by improving slope estimates. BvFTD subjects and caregivers will also complete behavioral, functional, QOL and caregiver burden assessments, where relationships with cognitive measures will be investigated. Measures requiring expert clinicians (Modified Clinical Dementia Rating, Neuropsychiatric Inventory, Clinical Global Impression of Change) will only be conducted at quarterly site visits. Contributing blood samples for DNA/RNA and biomarker explorations is voluntary. The minimal “standardized effect size” that can be detected in this study (considering 20% dropout) is 0.76 standard deviation units with 80% power and 0.05 significance level. For each cognitive outcome measure and composite measure, mixed-effects regression will be used to model both subject-specific and group-level slopes and estimate their within- and between-subject variance components. The study is currently in the start-up phase. Results will be presented at study completion. Identification of cognitive measures that are clinically meaningful, brief, sensitive to change, and predictive of bvFTD progression over short time would greatly benefit bvFTD drug development.

Temporal and Spatial Variances in Arterial Spin-Labeling Are Inversely Related to Large-Artery Blood Velocity.

The relationship between extracranial large-artery characteristics and arterial spin-labeling MR imaging may influence the quality of arterial spin-labeling-CBF images for older adults with and without vascular pathology. We hypothesized that extracranial arterial blood velocity can explain between-person differences in arterial spin-labeling data systematically across clinical populations. We performed consecutive pseudocontinuous arterial spin-labeling and phase-contrast MR imaging on 82 individuals (20-88 years of age, 50% women), including healthy young adults, healthy older adults, and older adults with cerebral small vessel disease or chronic stroke infarcts. We examined associations between extracranial phase-contrast hemodynamics and intracranial arterial spin-labeling characteristics, which were defined by labeling efficiency, temporal signal-to-noise ratio, and spatial coefficient of variation. Large-artery blood velocity was inversely associated with labeling efficiency (P = .007), temporal SNR (P < .001), and spatial coefficient of variation (P = .05) of arterial spin-labeling, after accounting for age, sex, and group. Correction for labeling efficiency on an individual basis led to additional group differences in GM-CBF compared to correction using a constant labeling efficiency. Between-subject arterial spin-labeling variance was partially explained by extracranial velocity but not cross-sectional area. Choosing arterial spin-labeling timing parameters with on-line knowledge of blood velocity may improve CBF quantification.

The effect of presentation level and stimulation rate on speech perception and modulation detection for cochlear implant users.

In order to improve speech understanding for cochlear implant users, it is important to maximize the transmission of temporal information. The combined effects of stimulation rate and presentation level on temporal information transfer and speech understanding remain unclear. The present study systematically varied presentation level (60, 50, and 40 dBA) and stimulation rate [500 and 2400 pulses per second per electrode (pps)] in order to observe how the effect of rate on speech understanding changes for different presentation levels. Speech recognition in quiet and noise, and acoustic amplitude modulation detection thresholds (AMDTs) were measured with acoustic stimuli presented to speech processors via direct audio input (DAI). With the 500 pps processor, results showed significantly better performance for consonant-vowel nucleus-consonant words in quiet, and a reduced effect of noise on sentence recognition. However, no rate or level effect was found for AMDTs, perhaps partly because of amplitude compression in the sound processor. AMDTs were found to be strongly correlated with the effect of noise on sentence perception at low levels. These results indicate that AMDTs, at least when measured with the CP910 Freedom speech processor via DAI, explain between-subject variance of speech understanding, but do not explain within-subject variance for different rates and levels.

FPCA-based Method to Select Optimal Sampling Schedules That Capture Between-subject Variability in Longitudinal Studies

A critical component of longitudinal study design involves determining the sampling schedule. Criteria for optimal design often focus on accurate estimation of the mean profile, although capturing the between-subject variance of the longitudinal process is also important since variance patterns may be associated with covariates of interest or predict future outcomes. Existing design approaches have limited applicability when one wishes to optimize sampling schedules to capture between-individual variability. We propose an approach to derive optimal sampling schedules based on functional principal component analysis (FPCA), which separately characterizes the mean and the variability of longitudinal profiles and leads to a parsimonious representation of the temporal pattern of the variability. Simulation studies show that the new design approach performs equally well compared to an existing approach based on parametric mixed model (PMM) when a PMM is adequate for the data, and outperforms the PMM-based approach otherwise. We use the methods to design studies aiming to characterize daily salivary cortisol profiles and identify the optimal days within the menstrual cycle when urinary progesterone should be measured.