Research in psychology and affective neuroscience often relies on film as a standardized and reliable method for evoking emotion. However, clip validation is not undertaken regularly. This presents a challenge for research with adolescent and young adult samples who are exposed routinely to high-definition (HD) three-dimensional (3D) stimuli and may not respond to older, validated film clips. Studies with young people inform understanding of emotional development, dysregulated affect, and psychopathology, making it critical to assess whether technological advances improve the study of emotion. In the present study, we examine whether 3D film is more evocative than 2D using a tightly controlled within-subjects design. Participants (n = 408) viewed clips during a concurrent psychophysiological assessment. Results indicate that both 2D and 3D technology are highly effective tools for emotion elicitation. However, 3D does not add incremental benefit over 2D, even when individual differences in anxiety, emotion dysregulation, and novelty seeking are considered.

Introduction

Every human experience is imbued with emotion [1], [2]. Emotions influence the perception of stimuli and subsequent course of action [3]. Emotions can facilitate or hinder social connection, attachment, and survival [4]. The manner in which emotions are experienced and regulated can alter physical health, academic and work performance, social functioning, and well-being [5]. Because healthy emotional development is a central task of childhood, adolescence, and emerging adulthood, there has been a steady increase in lab-based studies of emotion with young samples [6]. However, the tools used in affective neuroscience research often lag behind the technological context of today's youth.

Emotion research is founded upon the assumption that affective responses can be elicited and measured reliably in the laboratory. Ideally, the elicitation technique will evoke a replicable response while approximating the intensity of real-world stimuli. However, many lab-based protocols preserve one of these qualities at the expense of the other—methods with high internal validity often sacrifice ecological validity, whereas those that seek to replicate prior emotional experiences can lack methodological rigor. The presentation of emotionally evocative film clips offers one solution to this paradox [7], [8]. Film clips offer high reliability while also evoking commonly-experienced emotions. A disadvantage of this method is that visual technology is updated continually but not validated regularly as a research tool. Researchers have yet to test whether technological improvements (e.g., sharper resolution, larger screen sizes, better color reproduction) and/or new media formats (e.g., 3D) enhance the utility of film for research.

In recent years, studios have produced and promoted more 3D films, a trend matched by the home electronics industry. The ubiquity of 3D stimuli raises important considerations for researchers. Three-dimensional presentation could improve ecological validity, since the increased visual realism of 3D may mimic real-life emotional stimuli more effectively than 2D. If so, 3D technology would be valuable to affective neuroscientists, offering the same standardization and convenience as 2D film with increased validity. Nonetheless, 3D equipment is costly and requires the use of specialized glasses. More importantly, the majority of films are not produced in 3D. These limitations may have prevented researchers from examining 3D film as an emotion elicitation technique.

Over the past two decades, visual technology has advanced and there has also been a rapid increase in affective neuroscience research [9]. Technological improvements have allowed researchers to assess autonomic (ANS) and central nervous system (CNS) substrates of emotional responding more easily and at a lower cost. In particular, the costs of assessing ANS responses have dropped substantially, allowing more researchers to enter the field. Moreover, there are unique advantages to assessing ANS responses via peripheral psychophysiological techniques. These approaches are rooted in a rich theoretical tradition of emotion research, and the CNS correlates of peripheral measures are increasingly well-delineated [10]. Psychophysiological research can be conducted with a wider variety of protocols and stimuli within a shorter timeframe than most CNS measures. Finally, ANS assessments are especially well-suited for studies with younger samples or for those who do not respond well to the more invasive approaches used to measure brain activity. Thus, autonomic measures are foundational to emotion research.

Electrodermal and cardiac measures are among the most commonly used indices of emotional responding. Electrodermal activity (EDA) is the product of eccrine sweat gland activation, typically measured on the thenar eminence of the non-dominant palm. Because the eccrine sweat glands are enervated almost exclusively by cholinergic fibers of the sympathetic nervous system (SNS), EDA is a reliable index of SNS responding to affective stimuli [11], [12]. The central pathways that control EDA have been outlined across several animal and human studies [13]–[15]. Briefly, EDA is correlated with brain activation across regions that assess the significance of stimuli (e.g., the ventromedial prefrontal cortex, right inferior parietal region, and the anterior cingulate). When the stimulus has an emotional valence, the amygdala and orbitofrontal cortex are also activated, typically producing a more robust electrodermal response. Because the eccrine glands are less responsive to thermal changes, EDA can be linked to psychological processes such as attention, arousal, and emotion—especially if the task is selected carefully and the experiment is well controlled [16], [17]. During rest, the number of electrodermal responses is typically low and the eccrine glands remain in a tonic state. Phasic EDA increases in response to challenging tasks (e.g., mental arithmetic) or strong emotions (e.g., rage or fear). Two common measures of eccrine sweat gland activity include: (1) phasic EDA, which is the number of non-specific electrodermal fluctuations during a task and (2) tonic period, which is the amount of time spent in a non-responsive state.

Three measures of cardiac physiology include heart rate (HR), cardiac pre-ejection period (PEP), and respiratory sinus arrhythmia (RSA). Of these, HR is the most widely reported, perhaps because HR can be interpreted easily and is correlated with other measures of physical and emotional health [18]. However, activity of the cardiovascular system is affected by both the sympathetic (SNS) and parasympathetic (PNS) branches of the ANS. Furthermore, the SNS and PNS can affect HR reciprocally, coactively, or independently [19]. Thus, isolating the effects of sympathetic and parasympathetic activity is important for interpreting and conceptualizing the association between psychological constructs and cardiovascular output.

Increases in heart rate driven by the sympathetic nervous system can be measured with PEP, which is the time interval between left ventricular depolarization and the ejection of blood into the aorta. Shortened PEP intervals reflect stronger sympathetic activation in response to stimuli [20]. As with all psychophysiological measures, the interpretation of PEP as an index of psychological states depends largely upon the stimulus conditions [16]. For example, most healthy participants show attenuated PEP to fearful stimuli [21] and in response to monetary reward [22]. In other words, shortened PEP would be expected under conditions that elicit active avoidance or active approach.

Parasympathetic influences on cardiac activity are assessed with RSA, a measure of heart rate variability mediated by the vagus nerve [23]. The vagus exerts an inhibitory effect on cardiac output. During rest and conditions of low demand, inhibitory vagal control of HR is high, allowing the person to remain in a flexible regulatory state. In response to stressful stimuli, however, vagal control is withdrawn and HR increases so that the individual can meet environmental challenges. Following removal of the acute stressor, vagal activity returns to a tonic inhibitory state, allowing HR to return to baseline and attentional resources to be shifted away from the stressor. Among young adult samples, high RSA is usually associated with better modulation of attention and self-regulatory capacity [24]. Low RSA and more pronounced decreases during stress are often observed in clinical samples and under stimulus conditions that provoke emotion dysregulation [23], [25].

Although physiological responses to emotion-inducing films have been examined previously [7], it is unclear whether 3D film produces a more robust physiological response. Furthermore, it is unknown whether some participants are more receptive to the 3D effect. Three-dimensional stimuli could affect all participants uniformly or individual differences could moderate physiological responding to 3D. For example, higher levels of anxiety, emotion dysregulation, or novelty seeking could influence the extent to which a person responds physiologically to 3D. Evidence indicates that anxious individuals tend to shift attention toward threatening stimuli, whereas less anxious individuals direct attention away from threat [26]. Thus, 3D stimuli could produce a more robust electrodermal response among those who score high on trait anxiety, especially for clips that should provoke a strong sympathetic response (e.g., fear or excitement).

Novelty seeking (NS) is a personality trait characterized by an immoderate approach to reward cues, avoidance of monotony, and the pursuit of excitement. These impulsive personality traits are associated with striatal dopamine (DA) activity, especially under conditions that elicit approach motivation or behavior [16], [27]. Peripherally, PEP is a good marker of striatal DA activity during conditions of reward [16]. Compared with reward protocols (e.g., monetary incentives), passive viewing tasks are less likely to reveal large individual differences in PEP reactivity. However, participants who score higher on NS may be even less reactive to 3D technology (i.e., longer PEP), given that 3D technology is widespread and may be less exciting for those who engage regularly in thrill-seeking behaviors. Similarly, there may be individual differences in PNS reactivity to 3D. Across several studies, attenuated RSA has been linked to psychological problems characterized by emotional and/or behavioral dyscontrol [23]. Thus, participants who score higher on measures of emotion dysregulation may show less parasympathetic regulation (i.e., lower RSA) in response to 3D film.

Following from this review, the present study was designed to test whether 3D film is a more powerful elicitation technique for laboratory studies of emotion and whether individual differences might moderate the response to 3D. We assessed this in a large sample of young adults using electrodermal and cardiac measures of reactivity as objective markers of the affective response. Because 3D stimuli offer enhanced visual realism, we hypothesized that 3D film would evoke a more robust physiological response than the same clip in 2D. Furthermore, we hypothesized that some people may be more responsive to 3D, even if differences did not emerge for the full sample. Therefore, we examined individual moderators of physiological responding to 3D stimuli, including trait anxiety, novelty seeking, and emotion dysregulation.