Proposal: Use of Caloric Vestibular Stimulation to Identify Gender Differences in the Lateralization of Moral Processing

Moral judgments are the phenotypic projections of evolved, parallel, modular neural circuitry shaped over millennia by the demands of the social environment (Barbey, Krueger, & Grafman, 2009). Two of these modules may be categorized as moral-emotional and moral-reasoning, which together contribute to the judgments we make regarding “moral” stimuli.

Numerous experiments and high-tech functional imaging techniques have made clear that many of the brain’s abilities are anatomically lateralized, that is, they are the products of highly specialized processing modules asymmetrically distributed in either the left or right cerebral hemispheres. Recent evidence suggests that our moral judgments, too, are the product of competing modules, each physically positioned in one or the other hemisphere (Cope et al., 2010). Further, we have reason to believe that males and females employ subtly different processing strategies involving both the coordination and lateralization of contributing modules (Harenski, Antonenko, Shane, & Kiehl, 2008).

With these as our starting points, this study will explore potentially different male / female moral judgments using a safe, non-invasive, temporary stimulation of the vestibular nerve with ice-water irrigation, which creates a convective current in the fluid of the proximal semicircular canals (Miller & Ngo, 2007; British Society of Audiology, 2010). This stimulation has been shown to activate the insular cortex, temporo-parietal junction, superior temporal gyrus, and the anterior cingulate gyrus, among other areas (Miller & Ngo, 2007), all in the cerebral hemisphere contralateral to nerve stimulation. Studies using fMRI have shown many of these same regions to be involved in the processing of moral stimuli (Raine & Yang, 2006; Miller & Ngo, 2007; Mendez, 2009), making caloric vestibular stimulation (CVS) a particularly promising tool with which to identify sexual dimorphism of moral processing circuitry and integration strategies.

The existence of a “moral sense” has been deduced to explain normative, “universal” morality. This idea has recently received material support from functional magnetic resonance imaging (fMRI) studies, as well as theoretical development from the convergent approaches of evolutionary psychology, neurobiology, and social cognitive neuroscience. The emerging picture is one of morality as a pro-social, emotionally mediated “neuro-moral network” (Mendez, 2009). This network evolved in a demanding environment of ever-increasing social complexity in which the behavioral output of moral processing must have proved favorable for survival and reproduction (Funk & Gazzaniga, 2009).

Morality, then, can be understood as a behavioral strategy for survival in complex social environments, with successful social evaluation, judgment, and adaptive action as its components. Moral behavior, the system’s output, appears to be generated by competitive processing between parallel judgment systems of two broad types (two-process theory): emotional processing that produces the “feelings” associated with morality, and utilitarian processing that incorporates outcome probability with Theory of Mind. In fact, the subjective experience of Moral Dilemma may be understood in terms of conflict between these parallel judgment systems (Funk & Gazzaniga, 2009).

But if moral behavior is determined by unconscious processing and propelled by emotions, what role is left for conscious interpretation and choice? Certainly our subjective experiences suggest that explicit moral reasoning is at least somewhat involved in our moral judgments. Funk & Gazzaniga (2009) propose a different, counterintuitive conclusion: that the experience of moral reasoning is generated by a separate interpretive processor. This “interpreter”, they suggest, is concerned with generating coherent causal links between explicit social stimuli and our moral-emotional state, resulting in moral reasoning narratives constructed after automatic judgment processing has generated the behavior requiring explanation.

Restated, moral judgment is automatic and unconscious; the generation of narrative that makes sense of that judgment is mostly unconscious as well; the narrative generated by the “interpreter” (by correlating contextual information and descriptive moral convention) is the only artifact from the complex process of moral judgment and interpretive processing available to our consciousness, which we are generally disposed to accept as accurately reflecting our moral reasoning, just as we are disposed to presume our moral reasoning to be sound.

The chief contributor to our faculty of moral judgment appears to be neuro-emotional processing (J. Greene & Haidt, 2002), which generates the feelings of reciprocity, righteousness, consolation, guilt, shame, embarrassment, gratitude, compassion, pride, and outrage (Mendez, 2009). Moral conflicts have been found to elicit greater emotional distress than purely hedonistic conflicts, corroborating the status of emotion in driving moral behavior (Sommer et al., 2010). Antisocial, criminal, and psychopathic individuals share the inability to conform to societal norms largely because of a deficit in the “feeling” of what is moral, rather than a deficient understanding of moral norms (Raine & Yang, 2006), which again underlines the central role neuro-emotional processing plays in moral judgment.

Particularly relevant to this experiment, Greene and colleagues identified a close relationship between personal moral judgments and emotional processing (J. D. S. Greene, 2001). Conversely, the same study found impersonal moral judgments (where the subject was only proposed to be an indirect, rather than direct, agent of consequential action) to be more strongly associated with utilitarian processing centers.

By utilitarian moral processing, I refer to moral judgments that include either the quantification of outcomes, the estimation of probability (Shenhav & Greene, 2010), or belief attribution and mental state reasoning (perceiving and accommodating the intentions of others), i.e., Theory of Mind (ToM) (Young, Camprodon, Hauser, Pascual-Leone, & Saxe, 2010). Significantly, in cases where the intentions of others differ from the outcomes of their actions, split-brain patients have been shown to rely entirely on outcome, perhaps because their verbal response, formulated in the left hemisphere, lacks access to belief attribution processing of the right temporo-parietal junction (RTPJ). Further evidence has confirmed split-brain patients to be severely limited in tasks requiring integration of utilitarian and moral processing (Funk & Gazzaniga, 2009), with implications for the experiment hereafter proposed.

Lateralization and perception asymmetries (such as visual hemifield preference) are common among vertebrates (Vallortigara & Rogers, 2005). Language and motor control are widely recognized to be lateralized, but strong evidence for moral and emotional lateralization has arrived only in the last few decades. Two theories have emerged from studies of emotional lateralization: the right hemisphere and valence hypotheses, though neither has been well supported in studies of emotional moral processing based on Greene’s two-process theory.

As mentioned previously, utilitarian processing has been associated with right hemisphere lateralization, particularly involving the RTPJ (Young et al., 2010), while other studies have found left lateralization for moral judgment processing of negative morally laden stimuli in both linguistic and pictorial domains (Cope et al., 2010). This observed lateralization may reflect moral judgment processing itself, or may reflect ancillary processing activated by moral processing elsewhere.

Hypothesis 1: Main Effect of Gender on Agency, Value, and Processing

While males and females make similar evaluations of moral stimuli, they have been shown to engage different neural systems in doing so (Harenski et al., 2008). Female moral judgments are therefore predicted to involve more emotional moral processing, which in turn may affect judgments across agency and value levels when compared to males, who are predicted to recruit more utilitarian moral processing in response to EMJT. I predict that females will rate self-positive and other-negative statements as containing greater moral content than males do. Further, I predict that females will rate emotional statements as containing greater moral content than males do.

Hypothesis 2: Main Effect of Caloric Vestibular Stimulation on Agency, Value, and Processing

Lateralization of moral processing has been observed experimentally (Cope et al., 2010). Therefore, asymmetric disruption of normal moral processing via cerebral activation contralateral to caloric vestibular stimulation (CVS) is predicted to affect EMJT responses; subjects will significantly alter their pattern of responses across agency, value, and processing levels as measured by within-group repeated measures. Further, I predict left and right stimulations to have different main effects, as well as different interactions with gender.

Hypothesis 3: Interactive Effects on Agency, Value, and Processing

I predict that gender will interact with vestibular stimulation such that CVS effects, as measured by within group repeated measures, will differ between (gender) groups.

Methods

To test these hypotheses, subjects will first be screened; those cleared by a medical professional to participate will be placed into one of two groups based on gender. Each subject will be given a CVS control treatment using body-temperature (37°C) water irrigation of the outer canal, followed immediately by an Explicit Moral Judgment Task (EMJT). Once the task has been completed, a seven minute delay will be observed to avoid a carryover effect (British Society of Audiology, 2010). Each subject will then be given the iced water CVS treatment to either the left or right canal. Immediately following treatment delivery, an equivalent EMJT will be repeated. Again after a seven minute delay, the iced water CVS treatment will be administered to the other ear, with the EMJT following for a final, third time. The treatment orders will be counterbalanced across subjects and conditions. Once the protocol has been completed, subjects will be asked to remain until their balance has been fully restored. Safety will be confirmed using a “field sobriety” test.

Subjects, Screening

Prospective subjects will be recruited from participating psychology courses. Depending on the initial interest (or reluctance) shown, subjects may be recruited from the broader campus community as well. Interested parties must self-describe as healthy, right-handed, and either male or female to be considered as prospective subjects. Each prospective subject will be given a consent / screening form that makes explicit their permission for Berea College’s Health Services physicians to communicate the results of their screening to the principle investigator (PI). The consent form will also include the specific screening criteria so that potential subjects can make preliminary self-screening decisions at this first step of the process. If the prospective subject feels comfortable proceeding, an appointment with health services will be made for them. At the screening, a licensed physician will perform an examination of those items enumerated on the consent / screening form. At the conclusion of the screening, the physician will note the results and sign the consent form, which the student, if cleared, will return to the PI. It should be noted that only those prospective subjects who clear the screening examination will return the consent / screening form; if one or more of the exclusion criteria are detected during examination, that prospective subject’s examination results would not be reported to the PI – his / her results would be kept confidential by the attending physician and no further interaction with the PI is required.

Exclusion Criteria

• A diagnosis or family history of an axis I psychiatric disorder
• History of hypertension (uncontrolled, acute, or decompensated phase)
• History of eye or ear surgery within previous 6 months
• Diagnosis of epilepsy or any brain disorder such as a brain injury, tumor or other significant neurological disease
• Significant cardiac or respiratory disease
• Ear disease such as a perforated ear drum or otitis media/externa
• Vestibular disease or significant motion sickness
• Pregnancy
• Other contraindications
• Significant space occupying wax that cannot be sufficiently cleared
• Mastoid cavities

Subject Orientation

Those prospective subjects that pass the clinical screening and choose to continue by returning the signed form from Health Services will be scheduled for an experimental session, likely lasting approximately 1 hour. Upon arrival for the experiment, subjects will be introduced to the experiment’s purpose and methods. Each will be oriented to the equipment used and will be shown a short video demonstrating the procedure. An informed consent form will be required of each subject before the experiment begins.

Independent Variables

Within each experimental group [group 1, female; group 2, male], repeated measures of equivalent Explicit Moral Judgment Tasks (EMJT) following vestibular stimulations will be compared to determine the presence and significance of gender-based differences in the lateralization of moral processing circuitry. Caloric vestibular stimulation (CVS), a within-groups treatment, will have three levels: 1) a body-temperature treatment, and ice-water treatments of 2) the left ear and 3) right ear. The body-temperature treatment will be used as a control and should not produce a physical stimulation that would interfere with normal moral processing. The administration of body-temperature water will be alternated, within-group, between the left and right ear such that ½ of each group’s subjects receive the control treatment in the left ear, and ½ in the right ear.

Dependent Variables

Judgment scores based on moral agency, value, and processing will be measured as dependent variables. Moral agency will have two levels: self and other. Moral value will have three levels: negative, positive, and neutral. Moral processing will have two levels: emotional and utilitarian, which have been defined and discussed elsewhere in this proposal. Between and within groups, the EMJT responses will be compared to identify and measure gender-based and hemisphere-based differences between personal (self) and impersonal (other) agency, among negative, positive, and neutral values, and between emotional and utilitarian processing.

Subjects will be given twelve types of statements [self-positive-emotional, self-negative-emotional, self-neutral-emotional, other-positive-emotional, other-negative-emotional, other-neutral-emotional, self-positive-utilitarian, self-negative-utilitarian, self-neutral-utilitarian, other-positive-utilitarian, other-negative-utilitarian, other-neutral-utilitarian] and asked to evaluate each on a five point scale [morally very bad, morally somewhat bad, morally neither bad nor good, morally somewhat good, morally very good]. Each type will be comprised of a pool of 9 statements, for a total of [9*12=] 108 statements. Each EMJT will consist of 36 questions – 3 from each of the 12 types.

Group Design

Group 1 (Female)

1. ¼ receives: left cold + task; break; right cold + task; break; left control + task; recovery period
2. ¼ receives: right control + task; break; left cold + task; break; right cold + task; recovery period
3. ¼ receives: left control + task; break; right cold + task; break; left cold + task; recovery period
4. ¼ receives: right cold + task; break; left cold + task; break; right control + task; recovery period

Group 2 (Male)

1. ¼ receives: left cold + task; break; right cold + task; break; left control + task; recovery period
2. ¼ receives: right control + task; break; left cold + task; break; right cold + task; recovery period
3. ¼ receives: left control + task; break; right cold + task; break; left cold + task; recovery period
4. ¼ receives: right cold + task; break; left cold + task; break; right control + task; recovery period

Categories of Stimuli in Explicit Moral Judgment Tasks

• Moral Agency: self vs. other (18 each per task)
• Moral Value: positive vs. negative vs. neutral (12 each per task)
• Moral Processing: emotional vs. utilitarian (18 each per task)

Types of Statements in Explicit Moral Judgment Tasks

• Self-Positive-Emotional, e.g., “You volunteer at a local orphanage.”
• Self-Positive-Utilitarian, e.g., “You can only carry two of the three children across the street to safety, so one child is left behind.”
• Self-Negative-Emotional, e.g., “You burglarize your sister’s home.”
• Self-Negative-Utilitarian, e.g., “You steal from several lockers at the gym, though you know that only ¼ of them contain anything of value.”
• Self-Neutral-Emotional, e.g., “You eat your favorite lunch at noon each day.”
• Self-Neutral-Utilitarian, e.g., “You are unlikely to need your umbrella today, but you see your friend leave for class with hers.”
• Other-Positive-Emotional, e.g., “Jack volunteers to read to the elderly.”
• Other-Positive-Utilitarian, e.g., “Jill distributes the seven lifejackets among ten sailors on the sinking ship.”
• Other-Negative-Emotional, e.g., “Jill tortures her sister’s pet.”
• Other-Negative-Utilitarian, e.g., “Jack shot seven of his neighbor’s ten sheep, though two of the seven shot survived.”
• Other-Neutral-Emotional, e.g., “Jack sees a red convertible just like the one his dad drove.”
• Other-Neutral-Utilitarian, e.g., “Jill thinks she understands what her philosophy teacher means by a priori, though she suspects several in her class have misunderstood.”

Statement Evaluation Scale

• -2: “This is morally very bad.”
• -1: “This is morally somewhat bad.”
• 0: “This is morally neither bad nor good.”
• 1: “This is morally somewhat good.”
• 2: “This is morally very good.”

Recovery and Debriefing

Subjects will be given time in a safe place to regain their balance. Once the subject is confident of their own recovery, a field sobriety test will be administered. Once the recovered subject successfully passes the field sobriety test, no further precautions are deemed necessary and the subject will be free to go.

Subjects will be debriefed after the experiment (during the recovery phase) and given all pertinent information regarding the theories being tested. Additionally, each subject will be instructed to contact Health Services immediately if they experience any symptoms of depression, prolonged dizziness, nausea, or disorientation. Subject contact information will be collected before the experimental procedure. The results of the experiment will be communicated to each participant.

Statistical Analysis

A Mixed-design MANOVA test will be used to determine significance of variability across variables.

References

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