Running Head: EXTRAVERSION AND SENSORY DISCRIMINATION 1 Extraversion and Sensory Discrimination

The purpose of this study was to extend the electrocortical activity research in determining the biological bases of extraversion. Differences in auditory stimulation sensitivity have been previously found for extraverts and introverts, but there has been no focus on the potential differences in sensory discrimination abilities. Using event-related potential (ERP) techniques, this study’s focus is on the mismatch negativity wave (MMN)—an index of sensory discrimination—in determining possible the effects of personality on simple sensory tasks. Based on Eysenck’s arousal model, Brebner’s model of extraversion, and the adaptive model of the MMN, it was expected that extraverts would display significantly larger and less latent MMNs. ERPs were elicited from 64 female, undergraduate students, who were given the Eysenck Personality Questionnaire-Revised (EPQ-R), as well as the International Personality Item Pool version of Tellegen’s Multidimensional Personality Questionnaire (MPQ), to measure extraversion. A repeated measures mixed analysis of variance (ANOVA) was employed, and results contrary to expectations were obtained. Possible reasons as to why the hypothesis was not supported, the limitations of the study, and suggestions for future research are discussed. EXTRAVERSION AND SENSORY DISCRIMINATION 3 Extraversion and Sensory Discrimination Extraversion (E) is a personality dimension which has long been the subject of psychological research, is in many scales of personality—including the currently popular FiveFactor Theory (McCrae & Costa, 1999)— and whose definitions range from broad to narrow (Zuckerman, 2005). Eysenck viewed the typology of personality as essential to psychology as the development of the table of elements was for chemistry (Eysenck, 1973), and viewed personality types as clusters of several interrelated traits, and defined traits as significant intercorrelations between different habitual behaviours (Eysenck, 1990). In his factor analysis of personality, he found those high in E encompassing traits such as gregariousness, impulsivity, liveliness, dominance, and assertiveness, while those low in E encompasses the converse traits. These proposed traits of E echo early personality theorists, such as Jung, who defined E as the movement of all attention to the outside world— the social or physical environment (Jung, 1921). Exact definitions of E vary and evolve over time, and this is usually to complement ongoing research, making it clear the value of investigating biological bases of personality to further affirm, amend, and contribute to theoretical frameworks. Personality psychologist Gray (1973, as cited by Fowles 2006) noted that explanations for personality can be found in underlying psychological functions, and that the biological basis of these functions can be identified. Joireman and Kuhlman (2004) similarly state that a necessary criterion for theorizing a personality dimension is confirming its associated biological markers. Although imperative in the explanation of the individual differences in personality, and of paramount theoretical importance, a lucid understanding of the underlying biological bases of E have still not been obtained (Stelmack, 1990). EXTRAVERSION AND SENSORY DISCRIMINATION 4 Studying the biological bases of personality also has social relevance, as differences in personality, and accompanying traits, translate into differences in behaviour and preferences. An individual’s traits can be predictors of their life’s critical outcomes, such as physical health (Martin, Friedman, & Schwartz, 2007) and academic success (Chamorro-Premuzic & Furnham, 2003). People rating high in extraversion prefer and learn better with active discovery, while those low in E do better with passive learning (Eysenck, 1997). There is also a strong association between E and positive affect, although this is not a bidirectional relationship (Watson et al. 1999). These outward differences in behaviour have been attempted to be explained by many psychobiological theories. Psychobiological Theories of Extraversion By exploring the underlying biological bases, research could provide an explanation of trait behaviour— an enlightening etiology of personality, rather than a descriptive taxonomy (Clark & Watson, 2008). In understanding the evolution of research on the biological bases of personality, it is important to note the shift from top-down to bottom-up approaches. Eysenck started with personality theory and attempted to introduce constructs from biology in explaining individual differences. In contrast, Gray began with established behavioural and biological mechanisms (in animals) and attempted to explain which personality traits differences in these mechanisms would produce (Fowles, 2006). In either approach, understanding biological bases is essential for personality theory. Eysenck was one of the pioneering researchers to attempt to assimilate personality theory with a biological explanation. Eysenck (1967) explained the behavioural characteristics of extraversion (E) with his theory of arousal, which suggests extraverts have a lower level of cortical activity and a higher threshold of arousal than introverts. From this assumption, he EXTRAVERSION AND SENSORY DISCRIMINATION 5 suggested that extraverts have higher arousal thresholds than introverts, and therefore higher optimal levels of arousal by stimulation. Although the assumption of differing tonic levels of cortical activity was eventually not strongly supported by any empirical data, the concept more so served heuristic benefits to future research questions and findings. Eysenck's arousal theory played a seminal part in the development of Zuckerman’s theory of sensation seeking and optimal levels of arousal. In this theory, high levels of sensation seeking is associated with E, meaning that extraverts are seeking out environments high in stimulation while introverts are content with those low in stimulation (Zuckerman, 2005). Depue and Collins (1999) view agency (i.e. assertiveness and dominance) and affiliation (i.e. sociability) as part of a single characteristic they term ‘interpersonal engagement’, and impulsivity as the other central characteristic of E. Depue (2006) holds the view that E is an index of human variation in incentive-facilitated behaviour, with those high in E being high in such behaviour. He proposes that agentic E reflects the activity of a behavioural approach system based on positive incentive motivation. Rammsayer (2003) points out that as it focuses entirely on the mesolimbic DA system, it does not explain individual differences in sensory and motor functions in extraverts and introverts, which are thought to be mediated by another dopamine pathway: the mesostriatal DA system. Brebner (1983) proposed a model of E explaining differences in sensory information processing and motor functions, suggesting that extraverts experience stronger excitation from response organization, meaning they prefer fast responding and receive satisfaction from outward actions, while introverts experience stronger excitation from stimulus analysis. The former suggestion (faster motor movement for extraverts) has been supported by research using auditory stimulation (Rammsayer & Stahl, 2004). Differences found in sensory discrimination EXTRAVERSION AND SENSORY DISCRIMINATION 6 may help to clarify the reasons for the sensory information processing differences in this model. Mismatch Negativity Wave (MMN) Important research on extraversion using basic auditory stimuli has shown extraverts are less sensitive to sensory stimulation than introverts, thus showing smaller stimuli-responses on measures of electrocortical activity (Stelmack, Achorn, & Michaud, 1977; Stelmack, 1990). While there are studies looking at the differences in simple sensory detection and sensitivity of extraverts and introverts, there is little evidence showing their sensory discrimination abilities. Finding basic differences in these abilities would further elucidate the biological bases of extraversion. This issue was explored by Sasaki, Campbell, Bazana, and Stelmack (2000) by comparing extraverts with introverts, and possible differences in an event-related potential (ERP) associated with sensory discrimination, known as the mismatch negativity wave (MMN). ERPs are the electric potentials, or EEGs, that are time-locked to specific events (such as a sound). They are much smaller in voltage than EEGs, and are regarded as marker of underlying psychological processes occurring either in preparation or in result of the event. To discriminate ERPs from non-event-related background EEGs, all activity that is time-locked to an event (slight before and after the event) is averaged. The logic is that background noise (nonrelated EEGs) are not time-locked to the event and occur randomly, effectively reducing them and leaving genuine event-related potentials visible (Coles, 1990; Handy, 2005). The MMN wave is an ERP component that is elicited by any discriminable change in ongoing auditory stimuli. For example, when a participant is presented with a series of repetitive high-pitched tones (standard stimuli) with an infrequently occurring low-pitch tone (deviant stimuli), each time the deviant stimulus occurs an MMN will be elicited. It is obtained by subtracting the ERP waves to the standard stimuli from the ERP waves to the deviant stimuli, resulting in a difference EXTRAVERSION AND SENSORY DISCRIMINATION 7 wave. The MMN usually peaks in amplitude 150-250ms after the onset of a deviant stimulus and is most often reported at fronto-central and central scalp electrodes (Naatanen, 2007a). Its amplitude increases and latency decreases as the magnitude of sound change between the standard and deviant stimuli increases (Pakarinen et al., 2007). The MMN depends on the presence of sensory memory traces in the auditory cortex Naatanen, 2007a). When identical auditory stimuli are presented repetitively, a sensory-memory trace, or a representation, of them is formed. When the stimuli changes, the sensory input becomes incongruous with the representation of previous stimuli, and it is thought that the discrimination process of detecting this mismatch in sensory input and sensory memory traces is what elicits an MMN (Naatanen, 2007a). There is debate about the processes involved in the formation and comparison procedure for these sensory memory traces, but the adaptation explanation is the most fitting with current physiological views and findings on the auditory cortex and sound representation (for review, see: May & Tiitinen, 2010). The adaptive explanation is when a stimulus is repetitively heard (i.e. the standard stimulus), the neuronal populations responsive to this stimulus become inhibited from continually firing (constituting the sensory memory trace), thus increasing the excitability of neuronal populations responsive to other stimuli (i.e. deviant stimuli) (Naatanen & Winkler, 1999). The MMN is elicited regardless of the focus of attention; thus it is held that the stage of the discrimination process reflected by the MMN is an entirely pre-attentive (or pre-conscious) cognitive process (Naatanen, 2004). Accordingly, no cognitive task involving the auditory stimuli is required for elicitation. Usually participants are given a stimulating task (most often reading) that will direct their attention away from the ongoing stimuli as to avoid eliciting any attention-dependent ERP components that would contaminate the elicitation of true, pre-attentive EXTRAVERSION AND SENSORY DISCRIMINATION 8 MMNs (Naatanen, 2007a). The MMN is regarded by some as an index of pre-attentive auditory discrimination ability (Pakarinen et al., 2007). With increasing sensory discrimination accuracy, the MMN amplitude increases and latency decreases (Lang et al., 1990). Rather than indexing sensory detection ability, like the N100 wave, it is a unique objective measurement of sensory discrimination accuracy for various auditory attributes. Since different types of sound changes elicit different MMNs, this allows for the indexing and evaluation of discrimination acuity for several different auditory attributes (Naatanen, 2004; 2008). The MMN has uses not only in cognitive neuroscience research, but also clinical research and applications (Naatanen, 2007b). A prime example is its use as a reliable predictor of awakening from a coma (Fischer, 2006). Naatanen (2004) makes note of studies where the amplitude of an MMN to frequency change is attenuated (lessened) in dyslexic adults, and that this attenuation correlates with the severity of their reading problems (Kujala et al., 2001). Increased amplitude in frequency MMN have also been found for women with PTSD, a result theorized to indicate sensory process abnormalities perhaps accounting for the hypervigilance to environment and hyperarousal symptoms associated with the disorder (Morgan & Grillon, 1999). The MMN is becoming an index of underlying brain pathologies in schizophrenics (Naatanen, 2007b), as well as an index of the functional state of NDMA-receptor system (Umbricht, 2002), which is a system essential for the normal auditory processes of auditory discrimination and sensory memory (Jevitt, 1996). There is research on the relationship between the functional state of the NDMA-receptor system and dopamine activity, and its effects on extraverts as compared to introverts (Rammsayer, 2003). The MMN has also been used in studies on individual differences such as intelligence (Beauchamp & Stelmack, 2006; Bazana & Stelmack, 2002). Troche, Houlihan, Stelmack, and Rammsayer (2009) found that frequency MMN EXTRAVERSION AND SENSORY DISCRIMINATION 9 amplitudes were higher for individuals with high mental ability compared to those with low mental ability. They concluded that mental abilities are reflected by fundamental pre-attentive brain processes, which in turn are reflected by the MMN wave, and that differences in MMNs could be used as a tool to predict individual differences in mental ability. Although it has been found that both gender and personality traits do have an effect on individual variability of the MMN (Matsubayashi et al., 2008), research on personality using the MMN is sparse, with only one published study focusing on the differences between extraverts and introverts (Sasaki, 2000). Extraversion & the MMN Sasaki et al. (2000) employed changes in the frequency of tone, limiting it to a single MMN type. They reported the MMN was significantly larger in amplitude for extraverts than introverts, and suggest this reflects an attentional shift rather than pre-attentional processes, which is a reasonable speculation, as the significant difference was found in what is sometimes referred as a late-negative subcomponent of the MMN. Whether this is actually an ERP subcomponent or independent component is contested. Perhaps attributing it to extraverts’ susceptibility to becoming distracted by the deviant stimuli may give insight into the nature of this possible component and the processes which elicit it. This significant difference was found using an oddball paradigm at a slow-rate of stimuli presentation (a stimulus occurring every 1500ms), which may be too slow to gain a well formed sensory-memory representation of the standard stimulus, and is a not congruent with this study’s presentation paradigm. There is research on the MMN and personality traits related to extraversion. It has been found that high impulsive individuals had larger frequency MMN amplitudes than low impulsive individuals (Franken et al., 2005), and smaller MMNs have been found in those with depression (Ogura et al., 1993). Bar-Haim et al. (2003) found that socially withdrawn children have smaller EXTRAVERSION AND SENSORY DISCRIMINATION 10 frequency MMN amplitudes (and longer latencies) as compared to a control group. The purpose of this study is to extend the research of the influence of E on pre-attentive auditory processes and simple sensory discrimination abilities with the use of the MMN. Any differences found will be valuable for further understanding the biological bases and markers of E. As studies have shown that introverts are more sensitive to auditory stimulation (e.g. Stelmack et al. 1977; Doucet & Stelmack, 2000), it would follow that they would have less inhibited/more excited neuronal populations responding to standard stimuli to form a sensory-memory trace. In turn, they would have relatively less excitable neuronal populations responding to deviant stimuli, eliciting an attenuated MMN. In line with the arousal and sensitivity theory of E, and the adaptive explanation of sensory memory traces in the auditory cortex, this study hypothesizes that participants high in E will display larger amplitude, and shorter latency MMNs than those low in E. This hypothesized advantage in pre-attentive sensory discrimination could help explain why extraverts are less occupied with stimulus analysis than introverts, as in Brebner’s model (1983). The increasing potential clinical use of the MMN in an array of scenarios led to the necessary implementing of a quicker measurement method, with multiple types of deviants, without diminishing the accuracy of the results (Duncan et al., 2009). This study will be looking at pre-attentive auditory processing for a wide range of auditory changes; including changes in frequency, tone, duration, perceived location, and stimulus-continuity. This will be feasible by making use Naatanen's (2004) optimal MMN paradigm. Method Participants Participants (n = 64) were all female, undergraduate students completing the experiment EXTRAVERSION AND SENSORY DISCRIMINATION 11 for course credit. Gender differences with the MMN have been found (Ikezawa et al., 2008; Barrett & Fulfs, 1998), and in order to increase the power of this experiment we have restricted the study to female participants. Participants were asked to refrain from alcohol consumption 24 hours before the experiment, as well as nicotine and caffeine 1 hour before. Materials Personality Measures They were required to complete the Eysenck Personality Questionnaire-Revised (EPQ-R; Eysenck & Eysenck, 1991), as well as the International Personality Item Pool version of Tellegen’s Multidimensional Personality Questionnaire (MPQ; Goldberg et al., 2006), online before arriving to the experiment. Equipment & Acquisition Settings EEGs were recorded from 32 channels using an electrode cap with Ag/AgCl electrodes (EASYCAP GmbH, Germany). An electrode was placed on the nose as a reference. The amplifier (NuAmps, Neurosoft, Inc., U.S.) was set at a band pass of 100Hz and .50Hz. The software Neuroscan ACQUIRE application version 4.5 (Compumedics Limited, U.S.) was used to acquire EEGs. EOG below the eye and FP1 electrodes were used for VEOG, and FP1 and FP2 were used for HEOG. Naatanen’s Optimal Paradigm The stimuli types and presentation follow Naatanen’s (2004) paradigm. Participants were presented with the auditory stimuli binaurally via medical foam ear tips (Etymotic Research, Inc., U.S.). Standard stimuli were harmonic sinusoidal tones composed of 500, 1000, 1500Hz partials, with 5 ms rise and fall times, and were 75 ms in duration each. The frequency deviants were 10% lower (for all three harmonic tones) half the time, and 10% higher half the time. EXTRAVERSION AND SENSORY DISCRIMINATION 12 Similarly, intensity deviants were either 10dB lower or higher. For perceived sound source deviant differed in location from standard stimuli by 90 degrees. The duration deviant was 25 ms, rather than the standard 75 ms. The gap deviant had 7 ms cut out from the middle of the standard stimulus (1 ms fall and rise times included). Procedure Participants were shown into a separate room with a comfortable chair to sit in while watching an animated film of their choice. The presentation consisted of 1845 stimuli in three consecutive 5 min blocks. Stimuli were presented at a stimulus-onset-asynchrony (SOA) of 500 ms. Each block began with 15 standard stimuli, and from then on every other stimulus was a deviant. One deviant from each category (e.g. frequency) was played in the run of five deviants, and two identical deviants never followed each other. Offline Analysis The rejection criterion was anything above or below 75 mv. After filtering and EOG correction, the EEGs were visually inspected for any artefacts using Neuroscan Edit software version 4.5 (Compumedics Limited, U.S.). Epochs of 50 ms pre-stimulus and 450 ms poststimulus were separately averaged for the standard and for each type of deviant. Standard stimulus ERPs were subtracted from the corresponding deviant-stimulus ERPs, resulting in five difference waves. Results Analyses focused on differences between groups in MMN amplitude and MMN latency. After the exclusion of unusable EEG data, there remained 29 participants. These participants were assigned to either the Extravert or Introvert group after a simple median-split on their EPQR Extraversion scores. Statistical analyses included a mixed 10 X 2 X 3 (Condition [Intensity, EXTRAVERSION AND SENSORY DISCRIMINATION 13 Location, Gap, Frequency, Duration] X Group [Extraverts, Introverts] X Electrode [Fz, Fc1, Fc2, Cz]) repeated measures analysis of variance (ANOVA). There was a significant main effect of group for amplitude in the Gap condition, F (1, 27) = 4.105, p = .053. There was also an interaction effect for latency in the Frequency condition, F (3, 81) = 2.802, p = .045. T-tests revealed that extraverts had significantly smaller amplitude MMNs in the Gap condition. T-tests also revealed that introverts had significantly shorter latency MMNs in the Frequency condition for the Fz, Fc1, and Fc2 electrodes but not in the Cz electrode. Discussion It was expected that participants scoring high in E would display larger amplitude, and shorter latency, MMNs relative to participants scoring low in E. This was not supported by the current findings, and in fact the opposite was obtained from the analyses. These findings contradict the only comparable study (Sasaki et al., 2000), and provide only further ambiguity in lieu of clarity on the relationship of E and the MMN. There are many theoretical factors that further complicate any explanation of the findings, specifically the ongoing disagreements on explanations of how and where the MMN originates, and whether it is truly independent of the N1 (May & Tiitinen, 2010). If the MMN (assumed in this study as an index of change detection) is not functionally distinct from the feature analysis indexed by the N1, then the past research indicating that introverts display larger N1s would help explain our current findings of larger MMNs. Alternatively, there is research wholly supporting the functional distinction of the N1 and the MMN, reporting that the MMN is generated in a physically disparate location of the auditory cortex than the N1 (Pincze, Lakatos, Rajkai, Ulbert, & Karmos, 2001). Such contradictory findings on the MMN leaves relatively more room for speculation before explanation of these findings. EXTRAVERSION AND SENSORY DISCRIMINATION 14 Attention is an issue directly addressed in Sasaki et al.’s (2000) study, and is used as a possible explanation for the larger MMNs found in extraverts. This is at odds with the assertion that the MMN is elicited regardless of attention, which is in turn support for it indexing an entirely pre-conscious process (Naatanen, 2004). The independence of the MMN from attentional influence is contested: In comparing unattended to attended auditory channels in eliciting MMNs, significantly smaller negative waves were found for the unattended (Woldorff, Hackley, & Hillyard, 1991). In terms of Brebner’s model of E (1983), an increased excitation from stimulus analysis (as with introverts) may result in an increase in attention to the ongoing auditory stimuli, which (if not independent of attentional influence) could have increased the MMNs for introverts. The only significant group effect was obtained in the Gap condition, which consists of deviants that are standard stimuli with 7 ms cut out from the middle. It is reasonable to speculate that an individual more inclined toward stimulus analysis (i.e. an introvert) may allocate attention to this auditory blip of discontinuation in the Gap deviant that is noticeably different from the other deviants. The most apparent limitation of this study is the less than ideal sample size. Essential to ERP research, especially with components that are less easily elicited and isolated (MMN vs. N1), it is central to the reliability of results to have a large sample size (Handy, 2005). Tests of variance are very sensitive to non-normality (Markowski & Markowski, 1990), and a small sample size such as n = 29 is likely to yield questionable results. The reduced sample size was largely due to the necessity of excluding many trials because of artifactual bioelectrical activity (e.g. ocular movement, muscle movements, skin potentials), which will confound true ERP results. If replicated in the future, this study should focus primarily on increasing its sample size EXTRAVERSION AND SENSORY DISCRIMINATION 15 in order to obtain more reliable results, especially for a relatively harder to obtain ERP like the MMN; a sample size of n ≥ 100 would be a wisely cautious criterion. Variations in the auditory paradigm used to elicit the MMN, or even investigating visual sensory discrimination differences, may be of interest to future researchers. Additionally, differing measures of E (in either amount or type of measures) may be useful in determining true electrophysiological differences due to personality. This study’s findings, while contracting both past research and expectations, have serious implications for the study of personality, individual differences, and biological psychology. The ambiguity of the findings indicates that much more vigorous and precise research is required in order for light to ever be shed on the biological bases of personality. A serious blockade in this research is the ongoing disagreement about the MMN: it becomes difficult to say with certainty what MMN differences indicate for E when the theoretical underpinnings of the MMN are in doubt. In closing, although this study revealed data that upon first glance only complicates the issues at hand, the data does further illustrate the necessity of much more research before reaching any conclusiveness about the biological markers of E. EXTRAVERSION AND SENSORY DISCRIMINATION16 ReferencesMcCrae, R., & Costa, P. (1999). A Five-Factor theory of personality. Handbook of personality:Theory and research (2nd ed.) (pp. 139-153). New York, NY US: Guilford Press.Zuckerman, M. (2005). Psychobiology of personality (2nd ed., rev. & updated). New York, NYUS: Cambridge University Press.Eysenck, H. J. (1973). Eysenck on extraversion. Oxford England: Halsted Press Fowles, D. (2006). Jeffrey Gray's Contributions to Theories of Anxiety, Personality, andPsychopathology. Biology of personality and individual differences (pp. 7-34). NewYork, NY US: Guilford Joireman, J. J., & Kuhlman, D. M. (2004). 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