LOCUS OF CONTROL PREDICTS CORTISOL REACTIVITY AND SPEECH PERFORMANCE IN RESPONSE TO ACUTE

STRESS IN UNDERGRADUATE STUDENTS

Yvette Z. Szabo University o f Louisville

A ndrew C hang

California State University, Los Angeles

Cheryl C hancellor-Freeland San Jose State University

AbstractPrevious studies have found that an individual’s perception of control in a situation (Locus of Control; LOC) can serve as a protective factor that has physiological and psychological benefits. The present study examines LOC in an acute stress paradigm to examine the relationship between LOC and hypothalamic-pituitary-adrenal axis functioning as well as between LOC and performance. One hundred and thirteen participants at a metropolitan university were randomly assigned to ei­ther a stress or control condition. The stress condition consisted of the Trier Social Stress Test (TSST) while the control condition consisted of viewing a neutral travel video. Salivary cortisol was measured at four time points before and after exposure to the assigned condition. A mock job interview speech in the TSST was recorded and evaluated for performance on eight dimensions. LOC significantly predicted cortisol reactivity to the stressor in a multiple linear regression model. In addi­tion, LOC was a significant predictor o f speech performance in a sim­ple regression model. Cortisol was not related to speech performance, and LOC did not moderate this relationship, although LOC uniquely predicted speech performance. This research adds to a growing body of literature demonstrating physiological and functional influences of LOC orientation.

Keywords: locus of control, acute stress, cortisol, undergraduate stu­dents, Trier Social Stress Test, speech performance

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Although usually assumed to be only del­eterious, stress has the potential to enhance, hinder or show no impact on the performance of an individual. How well individuals do in stressful situations, such as workplace perfor­mance reviews, test-taking, and formal pre­sentations often depend on their perception of control and mastery. Stressful situations also activate the acute stress response, known as the body’s “fight or flight” response, a physiological and psychological response to physical and social demands. Many factors may influence the impact of stress, including detrimental or beneficial outcomes. Although perception of mastery seems to play an im­portant role in success, it is not the only factor that is influential because the biological stress system may be still present and active. Both perception of control and mastery and the bi­ological response have the potential to inter­fere with cognition and performance. While the literatures in both camps have developed separately, there is a need for understanding in their integration.

An individual can view a situation as a result of external or internal forces, known as one’s Locus of Control (LOC). LOC scores fall on a continuum between internal and external orientations. Lower LOC scores, or an internal orientation, indicate that one feels self-empowered and in control of his or her environment. Higher LOC scores, or a more external orientation, indicate that the individual feels they have less control of their environment and that outside forces shape his or her experience (Rotter, 1966). The ex­tent of control individuals believe they have over their environment (LOC) can influence perceived stress levels, such that a greater perception of control is related to lower per­ceived stress (Anderson, 1977; Hellhammer, Wust, & Kudielka, 2009; Roddenberry & Renk, 2010). While perceived stress and physiological stress may be positively cor­related, they are not extensions of one another

per se (van Eck, Berkhof, Nicolson, & Su- lon, 1996). Physiological stress is a result of nearly automatic cognitive and emotional ap­praisals of stimuli and perceived stress incor­porates the individual’s perceptions of their ability to handle the situation. This indicates that LOC may not be associated with physio­logical stress in the same pattern as it is with perceived stress. However, few studies have looked at LOC following the direct manipu­lation of stress. Therefore, further research is needed to determine whether perceptions of control can moderate the physiological acute stress response.

The acute stress response is located within the body’s corticotrophin-releasing hormone system. Responses to events deemed danger­ous or exciting begin with the activation of paraventricular corticotropin-releasing factor and arginine vasopressin neurons in the para­ventricular nucleus of the hypothalamus (Hell- hammer, Wust, & Kudielka, 2009; O’Connor, O’Halloran, & Shanahan, 2000). Corticotro­pin-releasing hormone then stimulates the release of adrenocorticotrophic hormone (ACTH; O’Connor et al., 2000). ACTH stim­ulates the release of cortisol, a glucocorticoid from the adrenal glands, activating the fight- or-flight response, which includes increased heart rate, suppressed immune function, and inhibited digestion. Under normal transient stress conditions, cortisol helps to successfully defend against a threat, and then is terminated by initiating a negative feedback mechanism to inhibit the hypothalamus’s corticotro­pin-releasing factor production (Sapolsky, 1994). Cortisol has been demonstrated to be a reliable index of the hypothalamic pituitary adrenal (HPA) chemical cascade, and it is a common biomarker for stress (Hellhammer et al., 2009). For this reason, the HPA axis and cortisol have been a focal point of recent stress research. Particular emphasis has been on factors that may be associated with blunted or heightened stress responses.

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Few studies have examined LOC and cor­tisol reactivity in acute stress contexts. The scant available literature on LOC and phys­iological responses to stress is both limited and mixed. For example, some studies have demonstrated that a more internal LOC is associated with reduced physiological activa­tion (Pruessner, Hellhammer, & Kirschbaum, 1999; Pruessner et al., 2005), and yet others found no association between LOC and phys­iological activation (Bollini, Walkter, Ha- mann, & Kestler, 2004; Pruessner et al., 1997). Flowever, varying methodologies seem to be confusing the state of the literature. For exam­ple, one study employed a cold-water stressor (Viena, Banks, Barbu, Schulman, & Tartar, 2012); another used computer tasks thought to induce a stress response (Pruessneret al., 1999) and still others used a combined speech and mental arithmetic psychosocial task (Pruessner et al., 1997). While the first two are well controlled laboratory measures, they lack generalizability outside of the lab envi­ronment. For applicability, a psychosocial stressor may have more ecological validity. Measures of cortisol have also been variable, one study used area under the curve cortisol over the length of the session (Pruessner et al., 1997; Pruessner et al., 2005), others correlated LOC with absolute cortisol output post-stressor (Viena et al., 2012) and others used change scores for the difference pre- and post-task (Bollini et al., 2004). Use of post­task values could be a large limitation due to individual differences in baselines. Delta cortisol values (i.e., post-talk minus baseline) may prove to be more informative to make comparisons across individuals or groups. While most studies used undergraduate stu­dent samples, another variation has been the gender representation, with a subsample of studies focusing on male participants (Pruess­ner et al., 1997). Importantly, measures of LOC have also differed. Across six studies of LOC and acute stress, four measures of

LOC were utilized. Differences in the con­struct measure may influence outcomes and conclusions. For example, some studies used the Questionnaire of Competence and Con­trol, a combined measure of self-esteem and LOC (Pruessner et al., 1997; Pruessner et al., 1999; Pruessner et al., 2005). However, when studies have looked at the constructs of perceived control separate from self-esteem (e.g. Scarpa & Luscher, 2002), greater base­line perceptions of control, or less helpless­ness, predicted post-task change in cortisol, but this was not a validated measure of LOC. Variations in the construct measured may contribute to the diverse findings. Finally, some of these studies examined performance independently in the context of acute stress, but few have examined the moderating role LOC may play. Overall, regardless of condi­tion, greater self-esteem and a more internal LOC on the LOC/self-esteem measure were associated with better performance (e.g. Pruessner et al., 1999). Still, the relationship between LOC and cortisol is mixed. This may be due to the breadth of stressors that have been employed. In sum, the general­izability of the results may be a function of the way in which the research questions have been assessed.

Past research has suggested a relationship between LOC and performance in a wide range of disciplines, such that a more inter­nal LOC is associated with better workplace and public speaking performance (Bemardi, 2011; Judge & Bono, 2001; Spector, 1986). For example, in a meta-analysis on four self-evaluation characteristics, job satisfac­tion, and performance, a more internal LOC was associated with higher job performance (Judge & Bono, 2001). In college students with new jobs, a more internal LOC was associated with perceiving stress as positive and resulted in higher achievement in their work role (Bemardi, 2011). A meta-analysis on employee perceptions of control found

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that greater perceived control, comparable to an internal LOC, was related to greater motivation and performance, as well as lower self-reported physical and emotional distress (Spector, 1986). In terms of public speaking, a more internal LOC is associated with less self-reported anxiety about communicating with others, and a more external LOC is as­sociated with less goal-directed speech and less motivation in communicating (Rubin, 1993). An internal LOC appears to provide a benefit for performance in a variety of set­tings; however, this body of research has not examined the role of physiological stress in these relationships.

One study examined the relationship be­tween LOC and performance under varying levels of stress to determine ifboth internals and externals follow the Yerkes-Dodson hypoth­esis of performance, where arousal increases performance for low levels of arousal and then negatively impacts performance at high levels of arousal (Guar & Upadhyay, 1988). Overall, performance increased over the stress levels, peaking at moderate stress, consistent with the Yerkes-Dodson hypothesis. There was a significant interaction between stress and LOC, divided into external and internal using a median split, such that under severe stress, internals maintained the high performance but externals performed significantly worse. While this article is dated, it is one of the first that looked at the three factors (LOC, stress and performance) in an a priori design to examine respective relationships.

Present Study

In order to better understand the relation­ship between LOC, performance and cortisol, the present study evaluated these associations following an experimentally-induced, acute stress paradigm. In this process, we observed the relationship of perceived control with the biological stress response and performance on a public speaking task. This builds on

past research by addressing several of the methodological limitations identified above. Specifically, this study used Rotter’s LOC scale, a frequently employed measure of in­ternal or external LOC across a wide range of domains, including psychotherapy outcomes and academic or occupational achievement (Baker, 1979; Parker, 2003). We also used an empirically-supported paradigm to induce psychosocial stress, the Trier Social Stress Test (TSST; Kirschbaum, Pirke, & Hellham- mer, 1993). The TSST includes both a public speaking and mental arithmetic component and has been demonstrated to induce a robust physiological response (Kirschbaum et al., 1993). Past research has examined perceived stress, which is not always representative of physiological activation (van Eck et al., 1996). Other research examined students during mid-term examination time, which introduces variables of preparedness and additional in­dividual differences that may confound find­ings (Viena et al., 2012). Manipulating stress experimentally allows for the examination of factors that may influence the HPA response to acute stress. Another benefit of using the TSST is that every participant is introduced to the same stimulus, an acute stressor, in a controlled environment.

While both the public speaking and math portion have a synergistic effect in making the TSST a reliable stressor, public speaking has a more ecologically-valid role. Public speak­ing is widely reported to be one of the biggest fears, one that causes tremendous amounts of stress for people (Richmond & McCroskey, 1995). Conversely, verbal communication skills are also ranked as the most desirable characteristic for employers (National As­sociation of College and Employers, 2011), indicating a need to better understand the fac­tors influencing effective communication and what may mediate apprehension and anxiety. One such factor may be LOC. Furthermore, to our knowledge, no previous study has

Cortisol Reactivity and Speech Performance in Response to Acute Stress / 229

experimentally manipulated stress and exam­ined the role LOC has on speech performance under stress. Therefore, the present study considered potential associations between LOC and performance following stress with the purpose of examining potential interplay between this perception and the biological stress system. Another goal is to establish the relationship between perceptions of control and actual performance under demanding and unexpected circumstances. In sum, the pres­ent study seeks to further clarify relationships of LOC on HPA functioning and speech per­formance in response to acute stress.

Hypotheses

The present study examines the relation­ships between LOC and both cortisol reac­tivity and speech performance in response to acute stress. The primary hypothesis is that there would be an inverse relationship with an internal LOC and cortisol reactivity, whereby a more internal LOC would predict a lesser degree of reactivity to the laboratory stressor. Our secondary hypothesis is that there will be a negative linear relationship between LOC and speech performance, such that a more internal LOC would predict better speech per­formance. Third, we examined whether stress differentially affects speech performance based on one’s LOC. We hypothesize that those with a more internal LOC will perform better on the public speaking task despite the relative increase in cortisol.

Methods

ParticipantsOne-hundred thirteen undergraduate stu­

dents were recruited from psychology courses at a metropolitan university. To be eligible for the study, participants had to be at least 18 years of age and currently enrolled in an undergraduate psychology course. Exclusion criteria included presence of a neuroendo­crine disorder, history of a psychological

disorder in the six months prior to the study, and currently taking psychoactive medica­tions. The sample was 75.2% female and ages ranged from 18-41 (M = 19.79,50 = 3.05). In addition, participants were ethnically diverse (22% Caucasian, 4.4% African American, 22% Latino/Latina, 31% Asian, 17% other and 1.8% N/A).

All participants provided informed con­sent and received course credit for participa­tion. The study protocol was approved by the local Institutional Review Board.

Measures

Screening and Demographics. Prior to the start of each research session, participants completed a brief screening questionnaire that asked about activities in the last hour. This was to ensure compliance with the pre-visit restrictions of not eating, drinking, smoking or exercising. It also evaluated whether the participant met eligibility criteria of not hav­ing a neuroendocrine disorder, not currently taking psychoactive medications, and not presenting with a psychological disorder in the past six months. Participants who did not meet eligibility criteria were not allowed to participate and those that violated pre-visit restrictions were rescheduled. Participants also completed a basic demographic form that inquired about age, gender, ethnicity, major, year in school, GPA, and English proficiency.

Locus of Control. To assess LOC, par­ticipants completed a 29-item self-report questionnaire, of which only 23 were scored (Rotter, 1966). The other six questions are filler questions. For each item, the participant was presented with two statements, one rep­resenting internal LOC and one representing external LOC. Instructions stated there was no right or wrong answer but to choose the state­ment that the individual agrees with most. En­dorsing the external statement earned a score of a 1. Responses were summed to create a total score that ranged from 0-23, where lower

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scores indicate an internal LOC and higher scores indicate a more external LOC. The range for this sample was 5-19. Cronbach’s al­pha for Rotter’s LOC scale has been reported to be between .65 and .80 (Lange & Tiggle- man, 1981; Rotter, 1966). Test-retest reliabili­ty over a two-year period has been reported to be .61 in a sample of Australian undergraduate students (Lange & Tiggleman, 1981).

Acute Stress Manipulation. The TSST takes approximately 15 minutes and involves both a speech and math task (Kirschbaum et al., 1993). First, experimenters led partici­pants into a room with a table that had a video camera and two judges. The room was kept regulated (e.g. temperature and light) and was free of decor. Participants prepared for the speech for three minutes in a different room and were instmcted that they would not be able to use their notes during the speech. At the end of three minutes, participants were asked to stand behind a line placed between the wall and the camera and gave a five min­ute speech in which they were instructed to “state your ideal job and convince the com­mittee why you are the best candidate for the job.” If participants paused for longer than 20 seconds, they were prompted by the main judge with “You still have more time, please continue.” Following the speech, participants completed a five minute mental arithmetic task counting aloud backwards from 2083 subtracting by 13 each time. These tasks were completed in the presence of two judges that were instmcted to maintain emotionless and only speak using scripted statements.

Speech Performance. As part of the TSST, each speech was recorded and evaluat­ed by a team of two judges on a scale of 8-40. A 5 point Likert Scale (1 = Poor, 5 = Great) was used for each of eight characteristics of performance (Organization, Persuasiveness, Content, Clarity, Volume, Speed, Profes­sionalism, and Friendliness). Examples of criteria assessed are maintaining eye contact,

consistently making friendly expressions such as smiles or gestures (friendliness), and keeping a constant pace of speech (speed). These characteristics were based on criteria suggested in studies of job interview perfor­mance and forms for evaluating interview performance (Hollandsworth, Kazelskis, Ste­vens & Dressel, 1979; McCarthy & Goffin, 2004). Inter-rater reliability was computed to be Cohen’s k = >.90.

Cortisol Reactivity. Participants gave four saliva samples during the study to assess salivary cortisol. The experimenter instmcted the participant to chew for one minute on cot­ton swabs that were placed inside Salivette® tubes with cotton swabs (Sarstedt AG & Co., Numbrecht, Germany). To ensure compli­ance, the experimenter remained in the room during the minute but turned away as the participant returned the cotton cylinder to the tube without using their hands. The samples were kept at 5 °C until analysis with ELISA assays with Expanded Range High Sensitiv­ity Salivary Cortisol Enzyme Immunoassay Kit (Salimeterics LLC, State College, PA). All samples were analyzed in duplicate for reliability purposes. The first sample was con­sidered the baseline sample and peak cortisol was the larger of the two samples given at 10 and 20 minutes post-task.

Procedure

Participants completed the experiment individually. All experiments were conducted between 12 and 6 pm to account for circadian rhythm cycles of cortisol (Kudielka, Schom- mer, Hellhammer, & Kirschbaum, 2004). The study began with informed consent and with an introduction phase where the experiment­ers clarified any questions about procedure and anonymity. Participants then gave their first baseline saliva sample and completed an eight minute neutral task which was part of a larger study, the results of which are not discussed in this paper.

Cortisol Reactivity and Speech Performance in Response to Acute Stress / 231

All participants were then randomly as­signed at a 2:1 ratio to either the stress or con­trol condition, respectively. Those in the stress condition completed the TSST. Participants in the control condition watched a neutral travel video for 15 minutes in lieu of the TSST. All other procedures were identical for each con­dition. After completing their assigned task, participants completed another neutral task that took approximately ten minutes. Saliva samples were collected before and after the task at ten minute intervals. Participants then had a 20 minute resting phase where they completed several questionnaires, including Rotter’s LOC scale and demographic informa­tion. Other questionnaires collected were part of a larger study and included a questionnaire on fitness and exercise, sleep habits and coping skills. After the resting phase, participants gave a final saliva sample and were debriefed.

ResultsThis study examined the relationships be­

tween LOC, speech performance and cortisol reactivity in a sample of undergraduate stu­dents at a metropolitan university. Of the 113 participants, 7 participants were removed for missing cortisol values, 4 were removed for having cortisol responses greater than 3 stan­dard deviations from than the mean and 3 were removed for not completing the LOC ques­tionnaire. This left a sample of 99 participants for data analyses: 65 in the stress condition and 34 in the control condition. Subjects who were removed from analyses did not differ in age (t —.649, p > .05) or ethnicity (j2 = 5.63, p > .05). They were, however, more likely to be in the experimental condition compared to the control condition (y l = 4.3,p = .04).

Gender has been shown to have a signifi­cant main effect on cortisol responses to the TSST (Kirschbaum et al., 1993), so gender was added as covariate predictor to models with cortisol variables a priori.

Delta cortisol was log transformed to re­duce positive skewness, all other variables met assumptions for normality. All means and standard deviations presented are untrans­formed. The criterion of significance was .05.

Manipulation Check

To assess the effectiveness of the TSST at inducing psychosocial stress, a univar­iate analysis of covariance (ANCOVA) was conducted comparing delta cortisol in nmol/L (Peak-Baseline) between the stress (M = 2.26, SD = 3.82) and control (A^-.19, «S!D=1.00) conditions. Gender was added as a covariate. This analysis showed a significant main effect of manipulation, F (1,98) = 7.37, p < .01, partial eta-squared = .071. Gender as a covariate did not reach significance, F (1, 98) = 2.51,/? =.12. This demonstrates the TSST was successful in producing a physi­ological response in those who completed it compared to those in the control group.

Hypothesis 1: LOC and Cortisol Reactivity to Acute Stress

To test the hypothesis that LOC would significantly predict cortisol reactivity to an acute stressor, a multiple hierarchal regres­sion was performed for the experimental condition. In the first step, gender accounted for 7.8% of the variance in delta cortisol, F (1, 63) = 5.29, p = .025. Gender was a sta­tistically significant individual predictor of delta cortisol, b = -2.51,/? = 025. When LOC was included in the second step, the model ac­counted for 16.4% of the variance in cortisol reactivity, F (2, 62) = 6.06,/? = .004. LOC was a significant individual predictor, b = .340,/? = .014, such that a more external LOC predicted higher increases in cortisol to the acute stress­or. Gender remained a statistically significant individual predictor, b = -2.521, p = .019, such that males demonstrated higher cortisol reactivity. Table 1 shows the full multiple re­gression model.

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Table 1 Hierarchical Multiple Regression Predicting Cortisol from LOC

b SEB PStep 1 (R2 = . 078)Gender -2.51 1.09 -.278*

Step 2 (A R2= .086)Gender -2.52 1.05 -.280*LOC .340 .135 .293*

Note: Total Model R^.164, *■= p < .05

Hypothesis 2: LOC predicting SpeechPerformance

To test the hypothesis that LOC would significantly predict performance on the speech of the TSST, a simple regression was performed. The model was significant and ex­plained 6.1% of the variance in speech perfor­mance, F (1, 62) = 4.04, p = .049. LOC was a significant individual predictor of speech performance, b = -.434, p = .049, such that a more internal LOC predicted better perfor­mance on the speech portion of the TSST.

Hypothesis 3: Moderation o f LOC in predict­ing speech performance

Due to LOC’s association with both delta cortisol and speech performance, a moder­ation model was used to test whether LOC moderated the effect of cortisol responses on performance. LOC and delta cortisol reactiv­ity were added in the together into the first step of a multiple regression model. The over­all model predicted 9.0% of the variance in speech performance, but was marginally sig­nificant, F (2, 61) = 3.021,/? = .056. LOC was a significant individual predictor, b = -.51, p =.02, but cortisol reactivity was not, b =.28, p= .\l. In the second step, a LOC and cortisol interaction term was added to the model. The overall model predicted 12% of the variance in speech performance but was only marginal­ly significant, F (3, 60) = 2.74, p = .051. LOC remained a statistically significant predictor,

b= -.65, p = .009. Neither delta cortisol nor the LOC by cortisol interaction term predicted speech performance. This regression model is shown in Table 2.

Table 2 Hierarchical Multiple Regression Predicting Speech Performance

b SEB PStep 1 (R2 = .090)Delta Cortisol .275 .197 .176LOC -.511 .221 -.291*

Step 2 (AR2= .03)Delta Cortisol -.902 .842 -.577LOC -.650 .240 -.370**Delta Cortisol X LOC .090 .063 .795

Note: Total Model R ^ . 120, *=p < .05, ** =p<.01

Discussion

This research sought to determine how perceptions of control affected biological reactions to acute stress and how those per­ceptions affected subsequent speech perfor­mance. Several key findings emerged from our investigations. First, LOC predicted cortisol reactivity to a laboratory stressor. Participants with a more external LOC re­sponded with higher cortisol responses to the TSST, supporting our first hypothesis. This indicates that if subjects view themselves as not having control over their environment, they are more likely to demonstrate a greater physiological response to an experimental paradigm. Our findings are in contrast with some prior research. For example, Bollini and colleagues (2004) concluded that corti­sol did not differ based on LOC orientation after using a noise stressor. This inconsistent finding may be due to differences in reactions to stressors utilized, the evaluative piece present in the TSST or the measure of LOC used. Conversely, our findings are consistent with research by Lundberg and Frankenhae- user (1978), who concluded that individual

Cortisol Reactivity and Speech Performance in Response to Acute Stress / 233

differences in subjective and physiological responses to stress (e.g. cardiovascular, adre­nal medullary, and adrenocortical reactions) are influenced by the extent to which the in­dividual feels events are outside their ability to control them.

Second, LOC negatively predicted speech performance, such that a more internal LOC predicted better performance on a public speaking task, supporting our second hypoth­esis. While, to the best of our knowledge, this is the first study to examine speech perfor­mance and LOC, this is consistent with some­what similar studies done with introductory college students. One study demonstrated those with an internal LOC were more likely to use facilitating anxiety and this relation­ship decreased as LOC became more exter­nal (Butterfield, 1964). The author described facilitating anxiety as highly adaptive and motivating in a stressful situation compared to debilitative anxiety, which is more mal­adaptive in that it limits success in a stressful situation, consistent with the Yerkes Dodson hypothesis of arousal. Similarly, students with a more external LOC showed higher test anxiety compared to those with an internal LOC, however, exam performance was not measured (Choi, 1998). In a study that used a mental arithmetic stressor (Walsh, Wilding & Eysenck, 1994), those with an internal LOC had a higher probability of giving a correct answer than those with an external LOC. Rotter (1966) also hypothesized that those with a more internal LOC would have a greater ability to control how they performed in certain environments, while those with an external LOC would exhibit greater difficulty maintaining performance.

Third, to confirm that LOC’s relation­ship to cortisol did not drive the subsequent relationship between LOC and speech per­formance, a multiple regression was run predicting speech performance from both LOC and cortisol. The overall model was

only marginally significant; this may be due to low power (post hoc power analysis = .66) from three predictors or, perhaps, shared variance between delta cortisol and LOC. However, despite this, LOC predict­ed speech performance and this was not attenuated by cortisol. This demonstrates that LOC predicts speech performance in­dependent of increased cortisol and should be investigated in larger samples.

LimitationsThere were a few limitations that should

be addressed. First, this was a convenience sample taken from college students enrolled in an introductory psychology course. Addi­tionally, this sample was primarily female, which is representative of the ratio of males to females in the psychology department at the university. Both factors limit our ability to generalize the findings outside of this pop­ulation. Future research should recruit more male participants in order to better examine these relationships and examine community populations. Males had significantly higher reactivity to the laboratory stressor in the final model. While some research has shown gender differences are due to estrus cycle variations (e.g. Kirschbaum et al., 1999), our lab has not replicated menstrual cycle or oral contraceptive gender differences, so our analyses controlled for gender and did not stratify by gender.

Additionally, our measure of speech performance, while formatted on empirical work, was created within our lab. Future research could be done assessing these criteria and could explore other areas of performance. It is worthy to note that the criteria assessed are consistent with recent descriptions highlighting the importance of examining variables such as content, and voice quality as well as eye contact and fa­cial expressions (Scherer & Volk, 2011).

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Broader Implications & Future Directions

To our knowledge, this research was the first to examine LOC, speech performance and cortisol reactivity using a laboratory stressor paradigm. We were able to demon­strate that cortisol did not account for the relationship between LOC and speech per­formance, indicating that LOC is an inde­pendent predictor for both cortisol reactivity and speech performance. In summary, this body of research demonstrates that LOC predicts both cortisol reactivity to an experi­mental stressor and performance on a public speaking task in a racially diverse sample of undergraduate participants.

This research adds to a growing body of literature that demonstrates functional dif­ferences between those with an internal LOC and those with a more external LOC. In terms of mental health, some research has shown a more internal locus of control to be associat­ed with lower depression (e.g. Gray-Stanley et al., 2010), though unrelated to anxiety (Wamecke, Baum, Peer, & Goreczny, 2014). While LOC’s stability as a personality characteristic is largely accepted, Legerski, Cornwall, and O’Neil (2006) determined that LOC is not stable, such that an internal LOC can become more external. In this study, the authors concluded this happened in reac­tion to layoffs in a steel working plant and were a reflection of the real constraints and opportunities an individual experiences in chronic unemployment or underemployment situations. Further, psychotherapy research has shown that LOC can be malleable and changes toward a more internal LOC over the course of therapy (Baker, 1979). Future research should examine whether one can manipulate perceptions of control, perhaps by priming an internal LOC to determine whether this develops resistance to mood and physiological reactivity. Further, chron­ic and acute stress often interact to predict disease (e.g. McEwen & Stellar, 1993) so the

impact of LOC on chronic stress may also be an important area to consider.

Further, performance in a public speaking paradigm is ecologically valid, but this is not the sole area of performance that could be experimentally examined. Tasks that focus on executive functioning, the ability to apply past experience to future activity, or working memory may provide additional insight into areas of performance influenced by LOC. Both of these domains (memory and execu­tive functioning) have been shown to be in­fluenced by stress (e.g. Holmes & Wellman, 2009) and may be a promising area of future research. The present study focused on corti­sol due to associations with memory, mental health vulnerability and hippocampal volume (e.g. Dickelmann, Wilhelm, Wagner, & Bom, 2011; Frodl & O’Keane, 2013; Stetler & Mill­er, 2011). However, other markers of stress physiological may also be examined.

LOC is an orientation that primes how in­dividuals view the environment and their role in situations. LOC may have diverse implica­tions for success in clinical, occupational and academic settings and merits future research for the extent that they can be explored and manipulated.

AcknowledgementsThis research was conducted within the

Psychology department of San Jose State University as a part of the work of the Inter­national Neuroeconomics Institute (INI) lab. This was partially made possible through a grant from the National Institute of General Medical Sciences (#5T34GM008253-23) to the MARC program at San Jose State Univer­sity. Additionally, we wish to acknowledge the members of the INI lab at San Jose State University for their help in data collection.

Cortisol Reactivity and Speech Performance in Response to Acute Stress / 235

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