Meta-analysis of genome-wide association studies for personality.

Personality can be thought of as a set of characteristics that influence people's thoughts, feelings and behavior across a variety of settings. Variation in personality is predictive of many outcomes in life, including mental health. Here we report on a meta-analysis of genome-wide association (GWA) data for personality in 10 discovery samples (17,375 adults) and five in silico replication samples (3294 adults). All participants were of European ancestry. Personality scores for Neuroticism, Extraversion, Openness to Experience, Agreeableness and Conscientiousness were based on the NEO Five-Factor Inventory. Genotype data of ≈ 2.4M single-nucleotide polymorphisms (SNPs; directly typed and imputed using HapMap data) were available. In the discovery samples, classical association analyses were performed under an additive model followed by meta-analysis using the weighted inverse variance method. Results showed genome-wide significance for Openness to Experience near the RASA1 gene on 5q14.3 (rs1477268 and rs2032794, P=2.8 × 10(-8) and 3.1 × 10(-8)) and for Conscientiousness in the brain-expressed KATNAL2 gene on 18q21.1 (rs2576037, P=4.9 × 10(-8)). We further conducted a gene-based test that confirmed the association of KATNAL2 to Conscientiousness. In silico replication did not, however, show significant associations of the top SNPs with Openness and Conscientiousness, although the direction of effect of the KATNAL2 SNP on Conscientiousness was consistent in all replication samples. Larger scale GWA studies and alternative approaches are required for confirmation of KATNAL2 as a novel gene affecting Conscientiousness.

Meta-analysis of genome-wide association studies identifies common variants in CTNNA2 associated with excitement-seeking.

The tendency to seek stimulating activities and intense sensations define excitement-seeking, a personality trait akin to some aspects of sensation-seeking. This trait is a central feature of extraversion and is a component of the multifaceted impulsivity construct. Those who score high on measures of excitement-seeking are more likely to smoke, use other drugs, gamble, drive recklessly, have unsafe/unprotected sex and engage in other risky behaviors of clinical and social relevance. To identify common genetic variants associated with the Excitement-Seeking scale of the Revised NEO Personality Inventory, we performed genome-wide association studies in six samples of European ancestry (N=7860), and combined the results in a meta-analysis. We identified a genome-wide significant association between the Excitement-Seeking scale and rs7600563 (P=2 × 10(-8)). This single-nucleotide polymorphism maps within the catenin cadherin-associated protein, alpha 2 (CTNNA2) gene, which encodes for a brain-expressed α-catenin critical for synaptic contact. The effect of rs7600563 was in the same direction in all six samples, but did not replicate in additional samples (N=5105). The results provide insight into the genetics of excitement-seeking and risk-taking, and are relevant to hyperactivity, substance use, antisocial and bipolar disorders.

The genetic association between personality and major depression or bipolar disorder. A polygenic score analysis using genome-wide association data.

The relationship between major depressive disorder (MDD) and bipolar disorder (BD) remains controversial. Previous research has reported differences and similarities in risk factors for MDD and BD, such as predisposing personality traits. For example, high neuroticism is related to both disorders, whereas openness to experience is specific for BD. This study examined the genetic association between personality and MDD and BD by applying polygenic scores for neuroticism, extraversion, openness to experience, agreeableness and conscientiousness to both disorders. Polygenic scores reflect the weighted sum of multiple single-nucleotide polymorphism alleles associated with the trait for an individual and were based on a meta-analysis of genome-wide association studies for personality traits including 13,835 subjects. Polygenic scores were tested for MDD in the combined Genetic Association Information Network (GAIN-MDD) and MDD2000+ samples (N=8921) and for BD in the combined Systematic Treatment Enhancement Program for Bipolar Disorder and Wellcome Trust Case-Control Consortium samples (N=6329) using logistic regression analyses. At the phenotypic level, personality dimensions were associated with MDD and BD. Polygenic neuroticism scores were significantly positively associated with MDD, whereas polygenic extraversion scores were significantly positively associated with BD. The explained variance of MDD and BD, ∼0.1%, was highly comparable to the variance explained by the polygenic personality scores in the corresponding personality traits themselves (between 0.1 and 0.4%). This indicates that the proportions of variance explained in mood disorders are at the upper limit of what could have been expected. This study suggests shared genetic risk factors for neuroticism and MDD on the one hand and for extraversion and BD on the other.

National character does not reflect mean personality trait levels in 49 cultures.

Most people hold beliefs about personality characteristics typical of members of their own and others' cultures. These perceptions of national character may be generalizations from personal experience, stereotypes with a "kernel of truth," or inaccurate stereotypes. We obtained national character ratings of 3989 people from 49 cultures and compared them with the average personality scores of culture members assessed by observer ratings and self-reports. National character ratings were reliable but did not converge with assessed traits. Perceptions of national character thus appear to be unfounded stereotypes that may serve the function of maintaining a national identity.

Personality and affectivity characteristics associated with eating disorders: a comparison of eating disordered, weight-preoccupied, and normal samples.

The purpose of this study was to assess the relative contribution of personality and emotional experience to self-reported eating attitudes in a group of patients with clinically diagnosed eating disorders, a weight-reduction training group (Weight Watchers), and a control group without body weight problems. Participants in this study (N = 114) completed Estonian versions of the Eating Disorder Inventory-2 (EDI-2; Garner, 1991), NEO Personality Inventory (Costa & McCrae, 1989), and Positive Affect and Negative Affect Schedule, Expanded Form (Watson & Clark, 1994). Data demonstrated validity of the Estonian version of EDI-2 in its ability to identify problems on a continuum of disordered eating behavior. Among the Big Five personality dimensions, Neuroticism made the largest contribution to EDI-2 subscales. Two other dimensions, Openness to Experience and Conscientiousness, also predispose individuals to eating problems. Personality traits made a larger contribution to the self-reported eating pathology than the self-rated effects experienced during the last few weeks. It was argued that personality dispositions have a larger relevancy in the etiology of eating disorders than emotional state.

The Estonian Self-Consciousness Scale and its relation to the five-factor model of personality.

The Self-Consciousness Scale (SCS), developed by Fenigstein, Scheier, and Buss (1975), was adapted to the Estonian language. In general, the results supported the 3-factor structure of the SCS. However, many items in the subscales did not load as expected. A 26-item modified scale, the Estonian SCS (ESCS), is presented. A joint factor analysis of the ESCS and the NEO Personality Inventory (NEO-PI) scales led to a 5-factor solution, where all the factors that emerged were identified as the Big Five personality dimensions, the ESCS subscales loading most significantly on 3 of these factors: Neuroticism (N), Extraversion (E), and Openness to Experience (O). Correlation analysis revealed a pattern of correlations, characterized by the strongest associations between Social Anxiety and E (r = -.77), Public Self-Consciousness (PubSC) and N (r = .40), and Private Self-Consciousness (PrivSC) and O (r = .34), which quite well corresponds to the pattern of correlations that was reported for the original versions of the SCS and the NEO-PI (Zuckerman, Kuhlman, Joireman, Teta, & Kraft, 1993). We can conclude that all the SCS subscales can be sufficiently well interpreted in terms of the Big Five model of personality dimensions--PrivSC and PubSC appear to describe some variations of the Big Five themes that are not fully elaborated by the NEO-PI rather than being completely independent domains of individual differences.

Language-specific phoneme representations revealed by electric and magnetic brain responses.

There is considerable debate about whether the early processing of sounds depends on whether they form part of speech. Proponents of such speech specificity postulate the existence of language-dependent memory traces, which are activated in the processing of speech but not when equally complex, acoustic non-speech stimuli are processed. Here we report the existence of these traces in the human brain. We presented to Finnish subjects the Finnish phoneme prototype /e/ as the frequent stimulus, and other Finnish phoneme prototypes or a non-prototype (the Estonian prototype /õ/) as the infrequent stimulus. We found that the brain's automatic change-detection response, reflected electrically as the mismatch negativity (MMN), was enhanced when the infrequent, deviant stimulus was a prototype (the Finnish /ö/) relative to when it was a non-prototype (the Estonian /õ/). These phonemic traces, revealed by MMN, are language-specific, as /õ/ caused enhancement of MMN in Estonians. Whole-head magnetic recordings located the source of this native-language, phoneme-related response enhancement, and thus the language-specific memory traces, in the auditory cortex of the left hemisphere.

Contrast response of a movement-encoding system.

The ability to identify the direction of apparent motion in a sequence of two short light pulses of different amplitudes at separate spatial locations was studied. The product of pulse amplitudes is a very poor predictor of such performance when one of the two signals is much higher in amplitude than the other: above a certain amplitude the probability of correct identification becomes virtually independent of the amplitude of the larger pulse. There was no noticeable difference in performance between low-high and high-low contrast sequences. Both the direction identification and the simple contrast-detection probabilities can be represented by the same psychometric function of the luminance increment delta L, provided that delta L is normalized by the nth power of the background luminance level, Lb. These results suggest that the general Reichardt-type scheme of movement encoding should be modified in the manner proposed for the fly's visual system [J. Opt. Soc. Am. A 6, 116 (1989)]: (1) the mean luminance is subtracted from the input signal before the signal is subjected to a nonlinear compression and (2) saturation characteristics are inserted into both branches of the two mirror-symmetric motion-detection subunits before multiplication of the input signals. The identical metric of the contrast response suggests that movement discrimination and luminance detection are two different special-purpose computations performed on the output of the same encoding network.

Magnitude of luminance modulation specifies amplitude of perceived movement.

A compelling impression of movement, which is perceptually indistinguishable from a real displacement, can be elicited by patterns containing no spatially displaced elements. An apparent oscillation, w-movement, was generated by a stationary pattern containing a large number of horizontal pairs of spatially adjacent dots modulated in brightness. The observer's task was to adjust the perceived amplitude of the w-motion to match the amplitude of a real oscillation. All of the data can be accounted for by a simple rule: If the relative change in the luminance, W = delta L/L, between two adjacent stationary dots is kept constant, the distance over which these dots appeared to travel in space comprises a fixed fraction of the total distance by which they are separated. The apparent amplitude of the w-motion increases strictly in proportion with luminance contrast, provided that the contrast is represented in the motion-encoding system by a rapidly saturating compressive Weibull transformation. These findings can be explained in terms of bilocal motion encoders comparing two luminance modulations occurring at two different locations.

Timing of visual events for motion discrimination.

The observer's task was to identify the temporal order of the two adjacent luminance excursions one of which was a step-function and the other a linear increase in luminance starting from zero and reaching various final amplitude A after some period of time D. The interstimulus delay, delta t, between these two transitions was determined at which they appeared isochronous. The point of the subjective equality (PSE) depended on both ramp parameters, the rise-time duration D and its amplitude A. All of the data can be accounted for by supposing that judgements about the temporal order are based on the comparison of a simple attribute of these luminance excursions, the time moments when the luminous energy concentrated on low temporal frequencies exceeds some level. The perceived temporal order, which was experienced as a leftward or rightward displacement of the whole pattern, was determined by the sequence in which low-frequency portion of these two luminance excursions reached the threshold value. The implications of this simple contrast detection explanation for theories of motion analysis are discussed.

Detection of changes in speed and direction of motion: reaction time analysis.

Observers reacted to the change in the movement of a random-dot field whose initial velocity, V0, was constant for a random period and then switched abruptly to another value, V1. The two movements, both horizontally oriented, were either in the same direction (speed increments or decrements), or in the opposite direction but equal in speed (direction reversals). One of the two velocities, V0 or V1, could be zero (motion onset and offset, respectively). In the range of speeds used, 0-16 deg/sec (dps), the mean reaction time (MRT) for a given value of V0 depended on magnitude of V1-V0 only: MRT approximately r+c(V0)/magnitude of V1-V0 beta, where beta = 2/3, r is a velocity-independent component of MRT, and c(V0) is a parameter whose value is constant for low values of V0 (0-4 dps), and increases beginning with some value of V0 between 4 and 8 dps. These and other data reviewed in the paper are accounted for by a model in which the time-position function of a moving target is encoded by mass activation of a network of Reichardt-type encoders. Motion-onset detection (V0 = 0) is achieved by weighted temporal summation of the outputs of this network, the weights assigned to activated encoders being proportional to their squared spatial spans. By means of a "subtractive normalization," the visual system effectively reduces the detection of velocity changes (a change from V0 to V1) to the detection of motion onset (a change from 0 to V1-V0). Subtractive normalization operates by readjustment of weights: the weights of all encoders are amplified or attenuated depending on their spatial spans, temporal spans, and the initial velocity V0. Assignment of weights and weighted temporal summation are thought of as special-purpose computations performed on the dynamic array of activations in the motion-encoding network, without affecting the activations themselves.

Perceived numerosity of spatiotemporal events.

Numerosity discrimination was examined when items were varied in space-time position rather than in space only. Observers were instructed to indicate which of two adjacent streams of visual events contained more items. The precision of numerosity discrimination of dynamic events was not remarkably different from that of static patterns. Two basic numerosity biases previously found for static dot patterns--inhibitory overestimation and satellite underestimation--were demonstrated for items distributed randomly over a spatiotemporal interval. It was also demonstrated that two streams, equated in the number and luminous energy of items, are not judged equal in their visible number if items in one of these two streams have longer duration than items in the second stream. These findings can be accounted for by the occupancy model of perceived numerosity (Allik & Tuulmets, 1991a) if it is supposed that the impact that each element has on its neighborhood is spread along both spatial and temporal coordinates. Perceived numerosity decreases with both spatial and temporal proximity between the visual items. Space and time have interchangeable effects on perceived numerosity: the amount of numerosity bias caused by the spatial proximity of items can also be produced by the properly chosen temporal proximity of items.

Resolving ambiguities in orientation, motion, and depth domains.

Three different perceptual systems--orientation, motion, and depth--can recover a global perceptual organization from spatially correlated random multielement patterns. In all three cases the global structure composed of random elements is evaluated by mechanisms performing measurements in the energy domain within appropriately defined local space-time areas. The selective increase in energy of one fraction of the elements may dramatically change the whole perceptual organization of the stimulus. In specially devised patterns one and the same element can belong to two or more separate perceptual organizations, the perceptual salience of one of which can be reinforced by a luminance increment of the elements comprising it. If a stimulus provides two different perceptual organizations to which each element could potentially belong, one of four possible solutions of the existing ambiguity will occur: suppression, rivalry, mixture, or parity. Two superimposed global orientation patterns either suppress or dominate over each other but cannot be seen simultaneously or in a mixed form. Characteristic of the depth system is that it allows multiple binocular matchings and parity of possible perceptual solutions. Finally, if a stimulus provides two or more paths along which each element may appear to move, the perceived global motion direction is determined by a mixture of directions of these competing motion paths. Dissimilarities in these ways of resolving ambiguities may be based on different principles defining regularity and coherence of an object in the orientation, motion, and depth domains.

Competing motion paths in sequence of random dot patterns.

Global motion perception from a sequence of random dot patterns has been studied by means of the competition technique which consists of making a normally less salient motion path in a superimposed multiple-path stimulus more powerful by adding luminous energy to elements forming this path. The perceived motion direction of a sequence of random dot patterns can be dramatically changed by increasing luminance of some fraction of dots leaving all spatial and temporal intervals between dots unchanged. The threshold luminance increment delta I that is required in order to change the perceived motion direction indicates that differently oriented local motion vectors are resolved into a single common motion vector along which the whole pattern appears to move. An inverse spatial proximity rule was discovered: within a certain spatial limit the motion strength of a particular motion path is proportional to the distance between stimulus elements forming this path.

Occupancy model of perceived numerosity.

Observers saw 234 different pairs of stochastically organized dot patterns and indicated which of the two patterns appeared to be more numerous. All of the data can be accounted for by supposing that the choice of the more numerous pattern is based on the determination of the occupancy indices of both patterns. Each dot is posited to have an impact upon its neighborhood in a constant occupancy radius R. The area of the stimulus plane occupied collectively by all dots provides a basis for judging relative numerosity; the pattern with the larger occupancy value is chosen as more numerous. The occupancy model, besides providing a general explanation of known numerosity illusions in strictly quantitative terms, can explain some puzzling aspects of numerosity perception.

Size invariance in visual number discrimination.

This study deals with the observer's ability to discriminate the numerosity of two random dot-patterns irrespective of their relative size. One of these two patterns was a reference one that was always composed of 32 dots randomly distributed within a K x K invisible square window (K = 1.92 degrees). The second one was the test pattern with one of the five magnifications (K = 0.64 degrees, 1.28 degrees, 1.92 degrees, 2.56 degrees, 3.20 degrees) and the relative number of dots varied on 11 levels (N = -15, -12, -9, -6, -3, 0, 3, 6, 9, 12, or 15 dots). The observer's task was to indicate which of the two patterns contained more dots. The results show that the stimulus size, as an irrelevant stimulus attribute, can be ignored in the judgements about relative numerosity. This means that the perceived numerosity is size invariant, at least for a 1.6-times magnification and a 3-times reduction of the test pattern. The size invariance observed constrains the range of potential models, since the perceived numerosity can be identified only by means of a feature of the stimulus that will remain invariant after any change in the absolute stimulus size.

Pitch motion with random chord sequences.

Perception of global pitch motion was studied through psychoacoustic experiments with random chord sequences. Chords contained either six or eight (fixed) tone elements, being sinusoidal, sawtooth-like, or Shepard tones, which were either on or off according to a probability controlled by the experimenter. Sequences of 2, 4, 5, or 8 chords were used. Identification by subjects of the perceived direction of overall pitch motion (up or down) was found to be well accounted for by a model in which the ultimate pitch motion percept is given by a sum of contributions from selected element transitions--that is, transitions between adjoining tone elements in successive time frames only. In its simplest form, this dipole contribution model has only one free parameter, the perceptual noise for an element transition, which was estimated for various acoustic tone representations and chord arrangements. Results of two experiments, which were carried out independently in two different laboratories, are reported.

Motion direction identification in random cinematograms: a general model.

The cinematograms of 12 two-state elements arranged in the clock positions in space and in a sequence of adjacent 100-ms frames in time were used as stimuli. Some positions in each frame (or all 12 of them) could be labeled as "domain" ones, and every element that was T frames and S positions (clockwise or counterclockwise) apart from a domain element could repeat the latter's state with probability P. The probability of the rotation direction identification was obtained as a function of T, S, P, number of frames, and the domain positions selection scheme. A generalized version of the reversed phi phenomenon was obtained: if P less than .5, then the psychometric value lies below .5 level. All the data can be accounted for by a simple model according to which the choice of direction is based on the counts of the different types of dipoles, each type being characterized by the probability and the weight of its count: In most situations all dipoles but the shortest ones (connecting the neighboring elements of successive frames) can be ignored.