The Need for a Neutral Speaking Period in Psychosocial Stress Testing

Various standardized protocols have been used to induce emotional and physiological stress in the laboratory. The cold pressor test, presentation of video clips, cognitive challenges like the Stroop task, and the Trier Social Stress Test (TSST; Bali & Jaggi, 2015) are routinely employed to capture the participants’ physiological response to a stressful stimulus. Typically, the physiological measures during the stressed state are compared to a silent, resting baseline period. The magnitude of the difference between these periods is considered the stress reactivity.

Many laboratory stressor tasks require the participant to speak, particularly those that rely on a social component to enhance stress induction. For example, personal narrative, such as describing an angering event from the past, is performed aloud to an interviewer (Kop et al., 2011; Lawler-Row, Karremans, Scott, Edlis-Matityahou, & Edwards, 2008; Maisto, Ewart, Connors, Funderburk, & Krenek, 2009). Mental arithmetic is also spoken to allow the researcher to assess whether answers are correct (McFadden, Healy, Hoversten, Ito, & Hernandez, 2012; Noto, Sato, Kudo, Kurata, & Hirota, 2005). One portion of the TSST, a “gold-standard” social-evaluative threat task originally developed to evaluate the hypothalamus-pituitary-adrenal axis but now used to assess wide-ranging physiological responses, requires participants to make a speech on why they should be hired for a mock employment position (Kirschbaum, Pirke, & Hellhammer, 1993). This speech has been modified to suit the needs of various studies, such as describing views of interpersonal violence and related Spanish legislation (Romero-Martinez, Nunes-Costa, Lila, Gonzalez-Bono, & Moya-Albiol, 2014), defending oneself from an accusation of shoplifting (Buchanan, Bagley, Stansfield, & Preston, 2012), or role play regarding an auto accident (Smith & Jordan, 2015), but all require verbalization.

However, when such stressor tasks are compared to a silent baseline period, it is impossible to differentiate between stress due to emotion/anxiety and stress due to the physical act of vocalization. Speaking itself does alter physiological measures, including heart rate (Seraganian, Szabo, & Brown, 1997), heart rate variability (Bernardi et al., 2000; Sloan, Korten, & Myers, 1991), blood pressure (Linden, 1991), and skin conductance (Crane, Dieker, & Brown, 1970; Tomaka, Blascovich, & Swart, 1994). Although a few attempts have been made to create a control task for the TSST (Het, Rohleder, Schoofs, Kirschbaum, & Wolf, 2009; Wiemers, Schoofs, & Wolf, 2013), these protocols are time- and staff-intensive, and these studies evaluated limited autonomic markers. The majority of the literature on the stress response still does not account for the effect of simply speaking aloud on physiological arousal.

Here, we propose a novel modification to a psychosocial stress protocol which can be implemented with little additional time or resources. By adding a period of neutral speech, we were able to quantify the effect of pure vocalization on a variety of autonomic stress responses and compare it to emotion-based responses. We hypothesized that there would be significant differences in physiological measures between the silent baseline and neutral speaking periods, and that these differences would explain some or all of the stress response traditionally attributed to emotion.

Materials and Methods

Stress Induction

Participants were tested between 14:00 and 17:00, having been awake for a minimum of 6 hr prior to their appointment. Participants were asked not to drink any alcohol in the 24 hr prior to the experiment, and not to eat, drink, exercise, or brush their teeth in the hour prior to testing. Participants were also instructed to drink caffeine according to their normal pattern of caffeine intake. Participants were sitting throughout the test, and two researchers were present during data collection.

The entire stress induction took less than 30 min (Figure 1). The data collection protocol began with a baseline period of participants sitting quietly for 5 min while listening to calming sounds (Calmsound, Seaside Ocean Sounds from a Golden Sand Beach.Mp3, Seaside 4). A 5-minute neutral questioning period followed the baseline period and consisted of asking participants questions that were not intended to be stressful. This portion of the test served as a comparative baseline measurement to account for the effect of vocalization on the stress response. Some questions were recommended as neutral control questions by the manufacturer of our skin conductance amplifier (iWorx, Inc., Dover, NH); other similar questions were added to extend the neutral questioning period to 5 min. The neutral questions utilized in this study were asked in the same order for each participant:

1. (1)
   Do you live in a dormitory?
2. (2)
   How many pets do you have?
3. (3)
   How many siblings do you have?
4. (4)
   Were you born in the United States?
5. (5)
   What year are you? (e.g., freshman)
6. (6)
   What is your major?
7. (7)
   Do you like chocolate?
8. (8)
   Do you like broccoli?
9. (9)
   Do you have a car?
10. (10)
    Do you like the beach?
11. (11)
    Where are you from?
12. (12)
    What is your favorite food?
13. (13)
    What is your favorite animal?
14. (14)
    How old are you?
15. (15)
    Do you play a sport?
16. (16)
    Do you play an instrument?
17. (17)
    Do you have a roommate?
18. (18)
    Have you traveled outside of the country?
19. (19)
    What is your favorite color?
20. (20)
    Do you have a bicycle on campus?
21. (21)
    Do you prefer more dressy or more casual clothes?
22. (22)
    Have you ever been to Texas?
23. (23)
    What day of the week is today?
24. (24)
    Have you gone to the movies in the past month?
25. (25)
    Are you right or left handed?

Questions were asked at a slow pace and not all participants finished all 25 questions. The average number answered within 5 min was 17 ± 2.8 questions.

The stressor periods consisted of verbal and math questioning. During the verbal questioning period, participants were asked a series of analogy questions taken from a previous Graduate Record Examination (GRE) exam for 5 min. This portion was included for a larger study in order to simulate an academic stressor. Participants were told after each question whether their answer was correct or incorrect. Questions were never repeated for the same participant. A math questioning period followed in which participants were asked to perform a serial subtraction task for 5 min. Participants serially subtracted 13 starting from the number 1,022 (or 1,033 on the second assessment) as quickly and accurately as possible. After every mistake, participants were asked to stop and start over from 1,022.

Results

Our sample of university students had scores similar to normative values (Herman et al., 2011; Roberti, Harrington, & Storch, 2006; Spielberger & Gorsuch, 1983) for state and trait anxiety (STAI-S and STAI-T), depressive symptoms (CES-D), and perceived stress (PSS-10) (ps > .05; Table 1). The CES-D means exclude one outlier scoring 52 out of 60 (severe depressive symptoms). The exclusion of this outlier did not change the conclusion that CES-D scores were not statistically different than the normative value.

Table 1 Psychological measure scores (M ± SD) of the sample compared to normative values from (Herman et al., 2011; Roberti et al., 2006; Spielberger & Gorsuch, 1983)

			Normative values
	Men (n = 14)	Women (n = 27)	Men	Women
Notes. STAI-S = State-Trait Anxiety Inventory, State subscale; STAI-T = State-Trait Anxiety Inventory, Trait subscale; CES-D = Center for Epidemiologic Studies Depression Scale; PSS-10 = Perceived Stress Scale. aMeans reported with one outlier removed (see text).
STAI-S	34.9 ± 10.3	38.8 ± 9.6	36.5 ± 10.0	38.8 ± 12.0
STAI-T	38.6 ± 13.0	42.6 ± 14.3	38.3 ± 9.2	40.4 ± 10.2
CES-Da	15.5 ± 9.9	16.3 ± 6.8	12.9 ± 8.5	15.4 ± 9.7
PSS-10	14.6 ± 5.8	17.7 ± 7.6	17.4 ± 6.1	18.4 ± 6.5

Table 1 Psychological measure scores (M ± SD) of the sample compared to normative values from (Herman et al., 2011; Roberti et al., 2006; Spielberger & Gorsuch, 1983)

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To determine whether the physiological indicators of the “emotional stress response” can actually be explained by participants simply speaking aloud, we determined whether there were statistically significant differences observed between the baseline and neutral questioning time periods, and whether the magnitude of these differences fully or partially accounted for the magnitude of the differences between baseline and the stressor periods. A main effect of period was found for systolic blood pressure, F(3, 90) = 1,377.6, p < .001, η_p² = 0.521) as well as diastolic blood pressure, F(3, 90) = 29.177, p < .001, η_p² = 0.493 (Figures 2A and 2B). The act of speaking neutrally contributed 42.4% of the magnitude of the peak stress response in systolic blood pressure, and 40.3% of the diastolic response. Similarly, a main effect of period was found for skin conductance level, F(1.657, 51.360) = 48.922, p < .001, η_p² = 0.612 (Figure 2C). For this physiological measure, 62.9% of the peak stress response was accounted for by neutral speech. The analysis of salivary alpha-amylase as a marker of sympathetic nervous system activity was a late addition to our methodology, so the sample size is limited (n = 12) and the data should be interpreted cautiously. However, even within this subset, a main effect of period was evident, F(3, 30) = 4.714, p < .01, η_p² = 0.320 (Figure 2D). The act of speaking neutrally contributed 35.8% of the magnitude of the peak alpha-amylase stress response. Normalized high frequency power of heart rate variability, as a measure of parasympathetic tone, also varied by period, F(1.9995, 70.385 = 6.904, p < .01, η_p² = 0.161 (Figure 3). Neutral speech alone accounted for 77.6% of the maximum drop in parasympathetic tone.

In order to see if these findings could be explained by changes in respiration rate between periods, we conducted a similar analysis of breaths per minute. Although a main effect of period was evident for respiration rate, F(2.002, 54.048) = 28.240, p < .001, η_p² = 0.511), with neutral speaking accounting for 76.8% of the peak response, the pattern of post hoc testing was not the same as the other physiological measures (Figure 4). Unlike other physiological measures, the neutral questions period is statistically different from the verbal questions period, but neither is statistically different from the math questions period. Additionally, the respiration rate did not correlate to any other physiological measure (r values between −0.22 and 0.04; ps > .05).

Discussion

The vast majority of the literature utilizing psychosocial stress testing does not account for the effect of vocalization in experimental procedures. Consistent with our hypothesis, we have shown that physiological measures such as blood pressure, skin conductance level, salivary alpha-amylase, and heart rate variability are significantly different between a neutral speaking period and a silent baseline. The common reporting of the change from a silent baseline to a stressor period as being the “stress response” is likely to be inaccurate when measuring the autonomic nervous system, as we have demonstrated that 36–78% of such a response can be attributed to vocalization alone. Although some attention has been given to measure the effect of speech on cortisol responses in the classic TSST protocol, this is less true for autonomic responses; in other commonly used psychosocial stressors (narrative recall, cognitive tasks like the Stroop test), investigators routinely do not account for vocalization at all.

The TSST was originally developed to induce a cortisol response (Kirschbaum et al., 1993), and it has been validated that cortisol does not rise due to vocalization using controls similar to our neutral speaking period. In the “friendly” TSST (Wiemers et al., 2013), participants are asked to speak about their life and career aspirations and then to read 30 words aloud to a panel of encouraging listeners. In the “placebo” TSST (Het et al., 2009), participants are asked to discuss a movie, book, or recent trip and perform simple addition in an empty room. A combination of reading aloud and then counting or simple arithmetic has also been used (Almela et al., 2011; von Dawans, Kirschbaum, & Heinrichs, 2011), or simply reading aloud (Rohleder, Wolf, Maldonado, & Kirschbaum, 2006). This work has established that the cortisol response in the TSST is emotion-induced, as it is robustly distinguishable from cortisol levels due to the simple act of speech. These protocols are valuable but time and resource intensive, as they have been implemented with a complete second session with the mock stressor, or a separate control group. This effectively doubles either the time required to conduct the experiment or the sample size required. We propose that the inclusion of one additional 5-minute period into an existing protocol is a more cost-effective and simple method to control for the effects of vocalization on measures of the stress response. Ideally, in future studies, such a period could be counterbalanced with the stressor period for even more robust measurements.

In contrast to cortisol measurements, the vocalization effect in the TSST on the autonomic nervous system has not been broadly assessed. This is regrettable because the original and modified versions of the TSST have often been used to induce sympathetic responses in addition to hypothalamus-pituitary-adrenal markers (Allen, Kennedy, Cryan, Dinan, & Clarke, 2014). The findings on the effect of neutral speech on the sympathetic nervous system in the TSST are mixed, and mostly limited to salivary alpha-amylase and heart rate. The alpha-amylase response to the placebo TSST (in one of two experiments) or friendly version of the TSST was indistinguishable from the traditional TSST (Het et al., 2009; Wiemers et al., 2013). Reading aloud with counting generated approximately 1/3–1/2 of the peak stress TSST stress response (Almela et al., 2011), and reading alone did not elevate salivary alpha-amylase at all (Rohleder et al., 2006). Heart rate rose approximately 1/3–1/2 of the peak stress response due to reading and counting (Almela et al., 2011; von Dawans et al., 2011), and reading alone caused an equivalent heart rate and heart rate variability response to the TSST (Rohleder et al., 2006). Previous authors (Het et al., 2009) have suggested that future studies explore expanded indicators of autonomic activity, which we have done here by assessing blood pressure, skin conductance level, and heart rate variability in addition to alpha-amylase. Combined with previous work, our data point to an autonomic nervous system response to stressors that is largely due to the act of speech rather than emotion.

An assertion could be made that the response we observed during neutral speech was not due to vocalization, but due to the novelty of the laboratory environment or anticipation of the stressors to come. However, the silent baseline period captures exactly these factors. Our baseline occurred in the same room and in the presence of the same researchers as during the stress period, and participants were aware of the protocol since the baseline occurred after informed consent. Thus, the inclusion of both the silent baseline and the neutral speaking periods allows a differentiation of anticipatory/novelty stress versus vocalization.

Our protocol is not intended to simply be an addition the TSST (in fact, we were not modeling our experiment on the classic TSST protocol with a committee), but is relevant to any psychosocial stressor that involves speech such as verbal arithmetic, narrative recall, or cognitive tasks. We propose that care should be taken to develop an emotionally neutral speaking control that matches the stressor task as much as possible. In reviewing previous work (Almela et al., 2011; von Dawans et al., 2011; Rohleder et al., 2006) we felt it was not ideal to introduce a new variable into a control task such as reading. Reading requires different cognitive resources than other tasks (Cabeza & Nyberg, 2000). It has been shown that reading aloud and spontaneous speech can have distinct timing characteristics (Bóna, 2014; Wang, Green, Nip, Kent, & Kent, 2010) and fundamental frequency (Hudson & Holbrook, 1982) that could influence physiological parameters. We propose that no control task will be perfect, but attention should be given to match cognitive modality with neutral emotional content as much as possible.

This leads to the difficult question of what is truly neutral content. We considered that some of our questions might provoke an emotional response from participants (e.g., asking if a participant has a pet could be upsetting if that person’s pet just died), but we anticipated that such an event would not affect the majority of participants. An additional concern was that a study examining the influence of specific types of words on the physiological stress response found that personal words, such as a participant’s major in college, produced greater skin conductance than either pleasant words, such as love, or aversive words, such as cancer (Crane et al., 1970). Since skin conductance level was captured continuously and we marked when each question was asked on the data file, we were able to analyze the mean conductance level following each individual question. No questions elicited higher conductance than others across the sample (data not shown), increasing our confidence that we chose questions that were usually neutral.

The changes we observed due to speech in blood pressure, skin conductance level, alpha-amylase, and heart rate variability were not correlated to respiration rate, so the effects are not due to simply a difference in breathing during speaking versus silence. Other factors, such as muscle tension or vibration of vocal cords (Hansen & Patil, 2007), could be explored in the future to understand this effect more fully. Elucidating factors such as these may help explain why subjective emotional stress often does not correlate to physiological responses in laboratory testing (Campbell & Ehlert, 2012).

It would be useful for a future study to explore if these results are similar in different populations. Our participants were limited to young adult college students. It is possible that older participants may feel more socially comfortable answering neutral questions in a laboratory environment, and thus the effect of neutral speech would be smaller. Alternatively, students may be accustomed to being asked a variety of questions by an authority figure due to regular experience in the classroom. Non-students may have a different response. It is also possible that the gender of the researcher could affect the perceived stressfulness of these tasks. Gender of the participant was not a statistically significant factor in our study except for systolic blood pressure, where men overall had higher values than women (data not shown); in all physiological measures, both genders showed the same pattern of change due to period. However, evaluating the interaction effect of gender of the participant and gender of the researcher would be a valuable inquiry. Since our experimental design included two researchers in the room with the participant, our sample size is not large enough to analyze all possible gender combinations with sufficient statistical power.

We believe these results have valuable implications for the field of physiological measurement of induced stress. It is not surprising that speaking induces sympathetic activation, and yet many experimental designs only use a silent baseline control. Multiple studies have used psychosocial stress testing to examine whether interventions, such as stress management, self-compassion training, meditation, or acupressure, were successful in reducing participants’ emotional stress response from pre- to post-intervention (Arch et al., 2014; Kemeny et al., 2012; McFadden et al., 2012; Rose et al., 2013; Vocks, Ockenfels, Jürgensen, Mussgay, & Rüddel, 2004). Without accounting for the effect of speech, it is not possible to determine whether an emotional stress response was induced in their participants in the first place, and how much that emotional response was mitigated versus the simple stress of vocalization.

Ethics and Disclosure Statements

All participants of the study provided written informed consent and the study was approved by the Institutional Review Board.

All authors disclose no actual or potential conflicts of interest including any financial, personal, or other relationships with other people or organizations that could inappropriately influence (bias) their work.