Sean D. Kristjansson

ECG biometrics: A robust short-time frequency analysis

In this paper, we present the results of an analysis of the electrocardiogram (ECG) as a biométrie using a novel short-time frequency method with robust feature selection. Our proposed method incorporates heartbeats from multiple days and fuses information. Single lead ECG signals from a comparatively large sample of 269 subjects that were sampled from the general population were collected on three separate occasions over a seven-month period. We studied the impact of long-term variability, health status, data fusion, the number of training and testing heartbeats, and database size on ECG biométrie performance. The proposed method achieves 5.58% equal error rate (EER) in verification, 76.9% accuracy in rank-1 recognition, and 93.5% accuracy in rank-15 recognition when training and testing heartbeats are from different days. If training and testing heartbeats are collected on the same day, we achieve 0.37% EER and 99% recognition accuracy for decisions based on a single heartbeat.

Laser Doppler Vibrometry Measures of Physiological Function: Evaluation of Biometric Capabilities

A novel approach for remotely sensing mechanical cardiovascular activity for use as a biometric marker is proposed. Laser Doppler Vibrometry (LDV) is employed to sense vibrations on the surface of the skin above the carotid artery related to arterial wall movements associated with the central blood pressure pulse. Carotid LDV signals are recorded using noncontact methods and the resulting unobtrusiveness is a major benefit of this technique. Several recognition methods are proposed that use the temporal and/or spectral information in the signal to assess biometric performance both on an intrasession basis, and on an intersession basis where LDV measurements were acquired from the same subjects after delays ranging from one week to six months. A waveform decomposition method that utilizes principal component analysis is used to model the signal in the time domain. Authentication testing for this approach produces an equal-error rate of 0.5% for intrasession testing. However, performance degrades substantially for intersession testing, requiring a more robust approach to modeling. Improved performance is obtained using techniques based on time-frequency decomposition, incorporating a method for extracting informative components. Biometric fusion methods including data fusion and information fusion are applied to train models using data from multiple sessions. As currently implemented, this approach yields an intersession equal-error rate of 6.3%.

Functional neuroimaging study in identical twin pairs discordant for regular cigarette smoking

Despite the tremendous public health and financial burden of cigarette smoking, relatively little is understood about brain mechanisms that subserve smoking behavior. This study investigated the effect of lifetime regular smoking on brain processing in a reward guessing task using functional magnetic resonance imaging and a co‐twin control study design in monozygotic (MZ) twin pairs that maximally controls for genetic and family background factors. Young adult (24–34 years) MZ female twin pairs (n = 15 pairs), discordant for regular smoking defined using Centers for Disease Control criteria as having smoked ≥100 cigarettes in their lifetime, were recruited from an ongoing genetic epidemiological longitudinal study of substance use and psychopathology. We applied hypothesis‐driven region of interest (ROI) and whole‐brain analyses to investigate the effect of regular smoking on reward processing. Reduced response to reward and punishment in regular compared with never‐regular smokers was seen in hypothesis‐driven ROI analysis of bilateral ventral striatum. Whole‐brain analysis identified bilateral reward‐processing regions that showed activation differences in response to winning or losing money but no effect of regular smoking; and frontal/parietal regions, predominantly in the right hemisphere, that showed robust effect of regular smoking but no effect of winning or losing money. Altogether, using a study design that maximally controls for group differences, we found that regular smoking had modest effects on striatal reward processing regions but robust effects on cognitive control/attentional systems.

Perceived Alcohol Stigma: Factor Structure and Construct Validation

INTRODUCTION There has been an increasing interest in studying the stigma of alcohol use disorders (AUDs) yet scant research has evaluated the conceptualization and measurement of alcohol stigma. This study examined the measurement properties (i.e., factor structure) and validity of the alcohol-adapted Perceived Devaluation-Discrimination scale (PDD), which assesses the construct of perceived alcohol stigma (PAS). METHODS Our sample included 34,386 respondents from the Wave 2 assessment in the National Epidemiologic Survey on Alcohol and Related Conditions, a population-representative survey of noninstitutionalized U.S. adults. Analytic procedures included confirmatory factor analysis and structural equation modeling. RESULTS One-factor (perceived devaluation-discrimination) and 2-factor (perceived devaluation, perceived discrimination) confirmatory factor analytic models fit the data well (Comparative Fit Index = 0.958, Tucker-Lewis Index = 0.942, Root Mean Square Error of Approximation = 0.056; Comparative Fit Index = 0.962, Tucker-Lewis Index = 0.946, Root Mean Square Error of Approximation = 0.054; respectively) when adjusting for item wording effects with a latent method factor. Despite having a better fit to the data, χ(2) (1) = 542, p < 0.0001, the 2 factors were highly correlated (r = 0.90), which led us to favor a 1-factor model. Structural equation models found that the inverse relationship between PAS and perceived interpersonal social support was strongest for persons with a stigmatized labeling status. The same was not true in analyses predicting social network involvement. CONCLUSIONS A 1-factor solution of PAS had superior parsimony. The alcohol-adapted PDD appears to be a psychometrically sound measure and exhibits relationships that are consistent with modified labeling theory.

Marijuana expectancies and relationships with adolescent and adult marijuana use

BACKGROUND Outcome expectancy is a central construct in models of addiction and relapse. Much expectancy research has been conducted in the context of alcohol; however, less is known about the structure of expectancies for marijuana and their associations with marijuana use outcomes. METHODS The data are taken from waves 3 and 4 of a longitudinal high-risk study of parents and adolescent offspring. Of those families who were retained at wave 3, 225 were high-risk and 205 were matched controls (low-risk). In the present study, we examine the factorial structure of marijuana expectancies (wave 3) in the offspring (using an instrument adapted from the alcohol literature) and test whether expectancies mediate the associations of familial risk for substance use, lifetime marijuana use in adolescence (wave 3) and current use in young adulthood (wave 4; reported approximately 5 years later). RESULTS We quantified four marijuana expectancy factors similar to those identified in previous studies when the offspring were adolescents (Mn age=15.2) and results of our mediation models suggest that negative marijuana expectancies (but not positive expectancies) together with lifetime adolescent marijuana use completely mediated the association between familial risk and current use of marijuana during young adulthood (Mn age=20.2). CONCLUSION Familial risk for current marijuana use in young adulthood appears to be transmitted through two orthogonal, prospective pathways. One pathway involves marijuana use during adolescence, and the second pathway involves reduced expectancies that using marijuana will result in cognitive and behavioral impairments.

Detecting phasic lapses in alertness using pupillometric measures

Small, nonreflexive pupillary changes are robust physiological indicators of cognitive activity. In the present paper, we examined whether measures of pupillary changes could be used to detect phasic lapses in alertness during a vigilance task. A polynomial curve-fitting method for quantifying parameters from single task-evoked pupillary responses (TEPRs) is described. The TEPR parameters associated with long latency responses (indicating low alertness) were compared to the TEPR parameters associated with normal latency responses (indicating an alert state) within a multilevel modeling framework. Three parameters, pupil diameter, linear pupil dilation rate and curvilinear pupil dilation rate, significantly differed between the long latency and normal latency response types. The results provide preliminary evidence that these parameters would be useful neurocognitive markers of operator state in a bio-behavioral alertness monitoring system.

Does Variance in Drinking Motives Explain the Genetic Overlap Between Personality and Alcohol Use Disorder Symptoms? A Twin Study of Young Women

BACKGROUND Genetic risk for alcohol dependence has been shown to overlap with genetic factors contributing to variation in dimensions of personality. Although drinking motives have been posited as important mediators of the alcohol-personality relation, the extent to which the genetic covariance between alcohol use disorder (AUD) symptoms (i.e., abuse and dependence criteria) and personality is explained by genetic factors contributing to variation in drinking motives remains unclear. METHODS Using data from 2,904 young adult female twins, the phenotypic and genetic associations between personality dimensions (constraint [measured by the Multidimensional Personality Questionnaire; Tellegen A, 1982 unpublished data], conscientiousness, neuroticism, and agreeableness [measured by the NEO-PI; Costa and McCrae, 1985]), internal drinking motives (enhancement and coping motives [measured by the Drinking Motive Questionnaire; Cooper, 1994]), and AUD symptoms were tested. RESULTS Significant genetic associations were found between all personality measures and AUD symptoms. Coping motives showed significant genetic overlap with AUD symptoms and most personality measures, whereas enhancement motives were not significantly heritable. Adjusting for coping motives, genetic correlations between AUD symptoms and traits of neuroticism and agreeableness were no longer statistically significant. CONCLUSIONS Findings suggest that genetic variation in drinking to cope might account for a considerable proportion of the genetic covariance between specific personality dimensions and AUD symptoms.

Smoking outcome expectancies in young adult female smokers: individual differences and associations with nicotine dependence in a genetically informative sample.

Outcome expectancy is a central construct in models of addiction. Several outcome expectancies associated with smoking cigarettes have been identified, and studies suggest that individual differences in smoking expectancies are related to important aspects of tobacco use, including levels of smoking, nicotine dependence and smoking cessation. In the present study, we used a novel analytic method, exploratory structural equation modeling (ESEM), to quantify smoking expectancies from a subset of items adapted from the Smoking Consequences Questionnaire (SCQ; Brandon and Baker, 1991) and SCQ-Adult (Copeland et al., 1995). In our sample of 1262 monozygotic and dizygotic young adult, female twins who were regular smokers, we quantified six smoking expectancy factors similar to those reported in previous studies. These included Negative Affect Reduction, Boredom Reduction, Weight Control, Taste Manipulation, Craving/Addiction and Stimulation-state Enhancement. We used genetic model-fitting to examine the extent to which individual differences in the expectancies were influenced by latent genetic, shared environmental and non-shared environmental factors. We also examined the validity of the expectancy factors by examining their associations with nicotine dependence (ND) before and after adjusting for comorbid diagnoses of drug dependence and alcohol use disorder. Results of the validity analysis indicated that all of the expectancies were associated with ND after covariate adjustment. Although we lacked the statistical power to distinguish between genetic and shared environmental sources of variance, our results suggest that smoking outcome expectancies aggregate in families, but the majority of variance in these expectancies is due to environmental factors specific to the individual.

Common Selective Serotonin Reuptake Inhibitor Side Effects in Older Adults Associated with Genetic Polymorphisms in the Serotonin Transporter and Receptors: Data from a Randomized Controlled Trial

OBJECTIVE Antidepressant side effects are a significant public health issue, associated with poor adherence, premature treatment discontinuation, and, rarely, significant harm. Older adults assume the largest and most serious burden of medication side effects. We investigated the association between antidepressant side effects and genetic variation in the serotonin system in anxious, older adults participating in a randomized, placebo-controlled trial of the selective serotonin reuptake inhibitor (SSRI) escitalopram. METHODS Adults (N = 177) aged ≥ 60 years were randomized to active treatment or placebo for 12 weeks. Side effects were assessed using the Udvalg fur Kliniske Undersøgelser side-effect rating scale. Genetic polymorphisms were putative functional variants in the promoters of the serotonin transporter and 1A and 2A receptors (5-HTTLPR [L/S + rs25531], HTR1A rs6295, HTR2A rs6311, respectively). RESULTS Four significant drug-placebo side-effect differences were found: increased duration of sleep, dry mouth, diarrhea, and diminished sexual desire. Analyses using putative high- versus low-transcription genotype groupings revealed six pharmacogenetic effects: greater dry mouth and decreased sexual desire for the low- and high-expressing serotonin transporter genotypes, respectively, and greater diarrhea with the 1A receptor low-transcription genotype. Diminished sexual desire was experienced significantly more by high-expressing genotypes in the serotonin transporter, 1A, or 2A receptors. There was not a significant relationship between drug concentration and side effects nor a mean difference in drug concentration between low- and high-expressing genotypes. CONCLUSION Genetic variation in the serotonin system may predict who develops common SSRI side effects and why. More work is needed to further characterize this genetic modulation and to translate research findings into strategies useful for more personalized patient care.

Drinking motives in female smokers: factor structure, alcohol dependence, and genetic influences.

BACKGROUND Alcohol and tobacco use often co-occur. Human and animal studies indicate that nicotine increases alcohols rewarding effects and the motivation to consume it. The aims of this study were to examine whether the factorial architecture of self-reported motivations to consume alcohol differed between regular and nonregular cigarette smokers while taking into account the lifetime history of alcohol dependence and psychopathology, and to estimate the genetic and environmental influences on the motivations. METHODS Using data on 2,189 monozygotic and dizygotic female twins, we examined the factorial structure (item thresholds and factor loadings, means, and variances) of the items from the Drinking Motives Questionnaire (DMQ) in regular and nonregular smokers. Post hoc tests examined the association between the latent drinking motives factors and alcohol dependence in both groups. Twin models were fitted to the latent drinking motives factors, testing for variations in the magnitude of additive genetic, shared, and nonshared environmental influences between the groups. RESULTS The 4 DMQ factors (social, conformity, coping, and enhancement) were recovered in both groups, and their measurement structure was consistent across the groups. Regular smokers reported higher levels of coping, enhancement, and social motives while nonregular smokers reported higher conformity motives. Alcohol dependence was associated with higher scores on all motives in both groups; however, in a regression analysis that included all of the motives as predictor variables, only coping was significantly related to alcohol dependence. While twin models revealed evidence for substantially greater genetic influences on enhancement (h² = 0.40), coping (h² = 0.35) and social (h² = 0.37) drinking motives in regular compared to nonregular smokers, the power to statistically distinguish the 2 groups was low. CONCLUSIONS While the measurement structure of the drinking motive factors appears to be similar across regular and nonregular smokers, regular smokers report more motivation to drink for internal affect-related reasons and to obtain social reward. Of all the motives, coping was the most robust predictor of alcohol dependence in both the regular and the nonregular smokers. Further, genetic influences might play a larger role in drinking motives among regular smokers, which provides tentative evidence for latent genetic × smoking status interactions.