Increased Amplitude And Latency Psychology Essay
Agentic extraversion, as a form of interpersonal behaviour, may play a role in personality disturbance; however the neurobehavioural system underlying this personality trait is not entirely understood by psychologists. This study aims to identify neurological difference between high and low agentic extraverts in response to auditory stimuli administered as part of a task using measurement of event-related potentials (ERPs). Participants were presented with three auditory stimuli (high frequency tone, low frequency target tone, rare complex tones) and requested to respond to the target stimulus by pressing a button. Results indicated that high agentic extraverts elicit larger amplitudes and longer latencies at the P300 when compared to low agentic extraverts. This indicates a longer processing time and greater response to the target stimulus, as well as increased attentiveness and more careful decision making among high agentic extraverts. Consequently, it appears that agentic extraverts may be less impulsive and potentially less likely to experience impaired behaviours seen in personality disturbances.
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Increased Amplitude and Latency at the P300 in Agentic Extraverts
Personality is often discussed in relation to five major personality traits; however research has shown little correlation between those and personality disorder diagnostic criteria. Four of those traits - extraversion, neuroticism, agreeableness and conscientiousness - have been demonstrated to have greater connection to many facets of personality than openness; however the neurological basis underlying these traits is still largely unknown (Depue & Lenzenweger, 2005). For this reason, psychologists have attempted to redirect their research towards the neurobehavioural systems which contribute to behavioural differences and, consequently, personality disturbance.
Personality disorders typically involve disturbances of interpersonal behaviour, which has two major components: affiliation and agency. Agency, also known as agentic extraversion, encompasses behaviours such as assertiveness, goal accomplishment, social dominance and efficacy. Psychologists have identified a neurobehavioural system underlying agency, which is one of two neurobehavioural systems implicated in directing behaviour towards rewarding goals. The neurobehavioural system underlying agency is more commonly known as the incentive motivation system and involves projection of dopamine within the limbic system. The incentive motivation system facilitates behaviour oriented towards positive stimuli through a process of classical conditioning which activates areas of the brain responsive to reward (Depue & Collins, 1999; Depue & Lenzenweger, 2005).
The incentive motivation pathway is implicated in agentic behaviour because it is associated with both goal directed behaviour and the affective state of reward. The incentive motivation pathway, referred to as the ventral tegmental area (VTA) dopamine (DA) projection system, involves the projection of DA from the VTA to the nucleus accumbens (NAS) which facilitates goal-oriented behaviour based on post-synaptic DA activation and the amount of incentive coming from a stimulus. Drugs that interfere with the projection of DA from the VTA to the NAS, the main projection area of DA from the VTA, demonstrate impairment in goal-oriented behaviours such as persistence. Dopamine antagonist drugs in animals reduce the number of attempted behaviour strategies; contrastingly, dopamine agonist drugs will increase the number of attempted strategies. Therefore, the amount of dopamine activity within the VTA DA projection system directly impacts the behavioural approach to potentially rewarding stimuli (Depue & Collins, 1999; Depue & Lenzenweger, 2005).
Richard Depue, an eminent researcher in extraversion, associated enhanced DA transmission with agentic extraverts because of their increased incentive motivated behaviours and response to rewarding stimuli. He proposed that increased transmission of DA within the VTA-NAS pathway facilitates reward-oriented behaviours that are demonstrated among agentic extraverts (Depue & Lenzenweger, 2005). For this reason, it is possible that people scoring highly in agentic extraversion would demonstrate a greater neurological response when encountering a target stimulus in a required task. Although agentic extraverts appear to have greater dopamine transmission in the VTA-NAS pathway, there is no clear indication of whether such extraverts demonstrate larger and faster neurological responses when completing a requested task. Brain activity measurements, such as electronencophalogram (EEG) during specific tasks among agentic extraverts may provide some insight. Specifically, time-locked electroencephalogram (EEG) measurements of brain activity, called event-related potentials (ERPs), may do this by measuring agentic extraverts' response to a specific stimulus.
ERPs reflect changes of voltages within the brain and provide an indication of neurological changes resulting from a person's environment (Rugg & Coles, 1995). The ERP of interest to this study is the P300, which manifests in the form of a positive trough in the wave at approximately 300 milliseconds post-stimulus. The standard paradigm used to elicit the P300 is the odd-ball paradigm, in which participants are exposed to a sequence of two different stimuli that are not equally as common in the sequence. Participants are asked to respond to the rare stimulus, often by pressing a button (Rugg & Coles, 1995). It is hypothesized that, given the increase in incentive motivated behaviour such as mental alertness and enthusiasm in agentic extraverts, that they will elicit a larger amplitude and shorter latency at the P300 than will people who score lower in agentic extraversion when responding to a requested stimulus (Morrone-Strupinsky & Depue, 2004).
All participants (n = 9) were undergraduate students enrolled in an Introduction to Psychology course at St. Thomas University in Fredericton, NB. Students were awarded credits in their introductory Psychology course for participating in the study and ranged between the ages of 17 and 19 (M = 18). Participants were required to refrain from alcohol consumption within 24 hours of their session, and to refrain from use of nicotine or caffeine for the hour prior to their session.
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All participants completed the Agency and Affiliation Questionnaire, a 102 item questionnaire derived from the International Personality Item Pool (IPIP) (Goldberg et al., 2006). The questionnaire included scales from the IPIP 16 PF, the IPIP NEOPI, the IPIP California Personality Inventory and IPIP Multidimensional Personality Questionnaire. All items were answered on a five-point likhert scale (very accurate, moderately accurate, neither accurate nor inaccurate, moderately accurate or very accurate). Results were used to categorize participants into groups of high agency (n = 4) or low agency (n = 5). Participants were also required to complete a section of demographic questions as well as a health questionnaire to screen for any extraneous health variables.
ERPs were recorded with an EEG electrode cap (32 channel Ag/Cl EASYCAP) and averaged using the computer software, Neuroscan Acquire. The following electrodes used standard placement as per the 10-20 International System: Fz, Pz, Cz, Fcz, EOG Fp2 (creating a bipolar recording) and linked mastoids (creating a reference) (Jasper, 1958).
An odd-ball task paradigm was used to administer two sequences of three different sounds. Both sequences were made up of a standard, high frequency tone; a target, less frequent, low frequency tone; and rare sounds such as animals or human voices.
Participants completed all questionnaires prior to their EEG session. Upon arrival, each participant signed a consent form prior to the experiment beginning and received a verbal explanation of the study. Participants were taken into a separate room where they sat and listened to a variety of auditory stimuli through headphones. Participants were instructed to respond only to the target stimulus (the simple, low frequency tone) by pressing the right button of a handheld device with their index finger. Participants were instructed to ignore all other auditory stimuli (the simple, high frequency tone and the complex, rare sounds). After completing both tasks, participants were debriefed and awarded their credits.
As previously mentioned, ERPs were recorded using the computer software Neuroscan Acquire. To extract signals from the EEG, free of artifacts such as blinking, an averaging technique was used. Several EEG epochs were averaged together, allowing the random background artifacts to level off at zero when averaged and consequently leaving only reactions time-locked to the stimulus (Rugg & Coles, 1995).
The high agency group demonstrated longer latency and larger amplitudes than did the low agency group at electrode Pz (Figure 1). On average, participants in the high agency group elicited a larger amplitude at electrode Pz by 3.14 microvolts (ÂµV) and a longer latency by nine ms when compared to the low agency group.
ï® = High Agency
ï® = Low Agency
Figure . Mean ERPs at component P300 for high and low agency groups.
Table 1. Mean amplitudes and latencies at electrodes Fz, Cz and Pz for high and low agency groups.
The present study hypothesized that participants with higher scores of agentic extraversion would display larger amplitudes at the P300 as well as shorter latencies. The results, as displayed in Table 1, confirm the hypothesis in relation to amplitude but dispute the latency hypothesis. High agentic extraverts had larger amplitudes by several microvolts but longer latencies by several milliseconds. This may reflect their increased motivation to complete the task assigned as well as their increased motivation to complete it accurately.
It was hypothesized that the high agency group would have shorter latencies on the basis of desire for efficacy with time. One might assume that, because an agentic extravert often prides themselves on being efficient, they may be motivated to complete the task more quickly. After viewing the results, agentic extraverts appear to take more time to process the stimulus, and therefore may be taking more time for evaluation prior to responding. The results better reflect behaviours of agentic extraverts than the hypothesis, because incentive motivated behaviours would be directed towards response accuracy instead of time efficiency. The use of time and correct response would produce a greater state of self-efficacy than a quick and incorrect response. Furthermore, increased attentiveness, as demonstrated by the greater amplitude at the P300 allows for greater feelings of reward following task completion. These two results indicate that agentic extraverts may be less impulsive in hopes of attaining greater reward. Depue and Lenzenweger (2005) suggest that agentic extraverts may be predisposed to delaying responses when doing so may produce more long-term and/or greater reward. Results from this study support Depue and Lenzenweger's implications by demonstrating a greater neurological processing time among high rather than low agentic extraverts.
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Although this study has demonstrated differences between the high and low groups of agency, future researchers may wish to employ larger sample sizes to see if the differences in latency and amplitude become greater with increased power. Future research may also benefit from recording response times and error rates between the two groups to determine if there is a relationship between neural processing time, response time, error rates and level of agentic extraversion.
Together, the increased amplitude and latency at the P300 among highly agentic extraverts demonstrates increased brain activation and increased processing time in response to a target stimulus when compared to mildly agentic extraverts. Agentic extraverts, who strive towards goals and reward, seem attentive, patient and thorough in their task completion. It appears that they are neurologically better able to strive toward long-term goals and delay gratification by displaying less impulsive behaviour. This has been displayed in the literature which demonstrates increased persistence and sense of reward among agentic extraverts and appears to be replicated by responses at the P300 in an odd-ball auditory paradigm (Depue & Lenzenweger, 2005).
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