Optimizar los insumos para la ejecución de los procesos y procedimientos de

The motivational model posits greater reactivity to emotional (pleasant and unpleasant) compared with neutral stimuli (Bradley & Lang, 2000; Hamm et al., 2003; Lang, 1995; Lang et al., 1990; Lang et al., 1997; Lang & Bradley, 2010). In contrast, a competing model of emotion processing is the negativity bias hypothesis which argues that the strength of activation between the appetitive and aversive systems varies in response to pleasant and unpleasant stimuli whereby aversive system activation is greater than

appetitive system activation in response to equally stimulating appetitive and aversive information cues (see Figure 2; Cacioppo & Bernston, 1994;

Cacioppo, Bernston, Norris, & Gollan, 2011; Ito, Cacioppo, & Lang, 1998; Norris, Gollan, Bernston, & Cacioppo, 2010).

Fulfilling appetitive and aversive system needs is imperative for the survival and evolution of humans. While satisfying appetitive needs such as hunger and sexual procreation is beneficial for long term survival, day-to-day survival is largely dependent on an individual’s ability to discriminate

threatening from non-threatening stimuli in their environment. While negative or unpleasant events are generally encountered less frequently than positive or pleasant events, the consequences of incorrectly responding to an unpleasant

event are more likely to be devastating compared to incorrectly responding to a pleasant event (Rozin & Royzman, 2001). These assumptions lead to the notion that the emotional and cognitive processing systems of humans have evolved into systems that facilitate rapid responses to unpleasant stimuli, and the observation that responses to aversive compared to equally stimulating appetitive stimuli are more rapid and pronounced, has been named the negativity bias (see Cacioppo & Berntson, 1994; Cacioppo et al., 2011; Cacioppo, Gardner, & Berntson, 1997; Ito & Cacioppo, 2005; Ito et al., 1998; Miller, 1959; Norris, et al., 2010; Rozin & Royzman).

Figure 2. Visual illustration of the negativity bias hypothesis.

Note. The negativity bias hypothesis proposes that responses to unpleasant stimuli are greater relative to pleasant and neutral stimuli, with greater reactivity to highly arousing relative to low arousing stimuli (stronger activation strength in aversive system). For cues: The apex of the triangle represents low arousing cues and the base of the triangle represents high arousing cues. The width of the triangle represents the level of cue arousal. For system activation: The apex of the triangle represents low system activation while the base of the triangle represents high system activation. The width of the triangle represents the level of system activation.

One of the main principles underlying the negativity bias is the concept of ‘negative potency’ which refers to the notion that highly unpleasant events are more threatening (negative) than equally intense pleasant events are positive. That is, negative stimuli/events are typically experienced with greater emotional reactivity than pleasant events, and responses to unpleasant events are generally more varied, leading to the greater influence of unpleasant events/stimuli (Cacioppo et al., 2011; Rozin & Royzman, 2001).

In summary, the negativity bias has evolutionary implications for protective behaviours as it is seen to facilitate rapid responses to aversive stimuli to optimise survival (Cacioppo & Berntson, 1994; Cacioppo et al., 1997; LeDoux, 2012). The negativity bias hypothesis stipulates that aversive system activation is greater than appetitive system activation in response to equally strong appetitive and aversive cues. This heightened aversive system activation results in greater reactivity to, and the prioritised processing of, unpleasant relative to pleasant and neutral information, with high-arousing stimuli eliciting greater reactivity than low-arousing stimuli (Cacioppo & Berntson; Cacioppo et al., 2011; Cacioppo et al., 1997; Ito & Cacioppo, 2005; Ito et al., 1998; Miller, 1959; Norris et al., 2010; Rozin & Royzman, 2001).

2.1.2.1. Negativity Bias Hypothesis: Behavioural and Physiological Evidence

The negativity bias hypothesis predicts greater reactivity to unpleasant compared to pleasant and neutral stimuli (Bradley et al., 2001a; Cacioppo & Berntson, 1994; Ito & Cacioppo, 2005). Numerous behavioural studies indicate a negativity bias in emotion processing as reflected by faster and more accurate responses to unpleasant relative to pleasant or neutral stimuli (Mogg et al.,

2000; Wentura, Rothrmund, & Bak, 2000). For example, to investigate emotional reactivity and the time taken for reactivity levels to decrease, Morriss, Taylor, Roesch, and van Reekum (2013) presented participants with pleasant, unpleasant, and neutral images followed by face stimuli, and

demonstrated that the reaction time to faces following unpleasant stimuli were faster than those following pleasant or neutral stimuli. Similarly, using a word grid task, Figueiredo (2015) demonstrated that reaction time to unpleasant stimuli were faster than to pleasant or neutral stimuli.

Additionally, self-reported ratings of valence and arousal levels have been shown to be modulated by emotional stimuli. Bernat et al. (2006)

collected valence and arousal ratings and assessed various physiological response systems including heart rate, SCR, startle reflex, and EMG while participants viewed pleasant, unpleasant, and neutral stimuli in a passive viewing task. Bernat et al. found that unpleasant stimuli were reported to be more unpleasant than the pleasant stimuli were considered pleasant. Similarly, Balconi, Falbo, and Conte (2012) obtained valence and arousal ratings and measured psychophysiological responses (SCR, heart rate, and EMG) while participants viewed low- and high- arousing pleasant and unpleasant stimuli in a passive viewing task and found that unpleasant stimuli were rated as more negative than pleasant and neutral stimuli with the emotional stimuli found to be more arousing than the neutral stimuli.

In addition to static emotional stimuli (i.e., emotional images), studies have demonstrated that film stimuli also show differences in valence and arousal ratings between stimuli, and evoke psychophysiological responses which may help to identify autonomic nervous system changes during emotion

processing. For example, Palomba, Sarlo, Angrilli, Mini, and Stegagno (2000) examined self-report valence and arousal ratings and psychophysiological responses (SCR and heart rate) while participants viewed film clips depicting neutral or unpleasant (surgery or threat of violence) scenes. They demonstrated that unpleasant film stimuli were rated as more unpleasant and more arousing than neutral film stimuli, with no differences in valence or arousal ratings revealed between the two unpleasant film categories of surgery or violence.

In addition to valence and arousal ratings of emotional stimuli,

physiological responses have been shown to vary with the emotional content of picture stimuli. For example, in studies including that of Balconi et al. (2012) described above, SCR has been shown to be larger to unpleasant relative to pleasant and neutral stimuli and greater to high- relative to low- arousing or neutral stimuli, with Balconi et al. also showing that high-arousing unpleasant stimuli elicit larger SCR than neutral and low- and high- arousing pleasant stimuli. Studies containing film stimuli have also demonstrated SCR to be greater during exposure to unpleasant threat films compared to neutral films (Palomba et al., 2000). Similarly, previous studies (e.g., Balconi et al.) have reported a consistent relationship between EMG activity and valence and arousal whereby EMG response is greater for unpleasant compared to pleasant or neutral stimuli, with high-arousing unpleasant stimuli eliciting enhanced EMG relative to neutral and low- and high- arousing pleasant stimuli.

Heart rate evidence while exposed to emotional and neutral stimuli during passive viewing tasks has also been reported to provide support for the negativity bias. In general, it has been shown that when participants view emotional images, sustained cardiac deceleration occurs, with the largest

decelerations occurring during the viewing of unpleasant scenes relative to pleasant or neutral stimuli. For example, unpleasant stimuli elicited a decelerated heart rate response relative to pleasant and neutral stimuli in studies by Bernat et al. (2006) and Balconi et al. (2012). Moreover, Balconi et al. demonstrated that high-arousing stimuli produced more heart rate

deceleration than low-arousing or neutral stimuli. Interestingly, heart rate evidence for the negativity bias hypothesis has also been documented in

studies using film stimuli as unpleasant (threat) film have been shown to evoke an increase (as compared to decrease as most commonly reported) in heart rate compared to a neutral film (and unpleasant (surgery) films which did not differ from a neutral film) (Palomba et al., 2000). Taken together, these studies show the occurrence of distinct cardiac patterns during the viewing of unpleasant stimuli. This cardiac activity is represented by both the classic defence pattern in response to unpleasant stimuli (i.e., fight/flight response) reflected by acceleration in heart rate associated with sympathetic activation, and a more complex autonomic reaction characterised by heart rate deceleration related to sympathetic cardiac withdrawal (e.g., avoidance) or increased parasympathetic cardiac control (Balconi et al.; Bernat et al.; Palomba et al.).

The startle reflex paradigm is commonly used in emotion processing research and involves the presentation of a loud, abrupt, and unexpected sound which elicits a startle response in both humans and animals (Koch, 1999). The startle response is modulated by the brainstem and limbic network, consists of a rapid and involuntary blink, and is considered to be a reflex. Some studies (e.g., Bradley, 2000; Bradley & Lang, 2000; Lang et al., 1997) have produced evidence of increased startle reflex to pleasant stimuli, which provides support

for the motivational model.However, the majority of studies show that when elicited in different emotional contexts the potentiation of the startle reflex is significantly increased in the presence of threat, fear, and pain (Bernat et al., 2006; Bianchin & Angrilli, 2012; Grillon, 2008). The startle response can subsequently be used as a measure of defensive system activation as it reflects automatic arousal/reactivity and provides a non-invasive physiological index of fear (Grillon). Supporting the negativity bias, the startle reflex has been shown to be larger in response to unpleasant relative to pleasant stimuli (Bernat et al.). Similarly, unpleasant films provoked increased probability of a startle reflex occurring as well as increased startle reflex amplitude when compared to neutral films (Palomba et al., 2000).

2.1.2.2. Negativity Bias Hypothesis: Neuroimaging Evidence As was discussed in detail above, there is a group of cortical and subcortical brain networks which underlie emotion processing. For example, neuroimaging evidence outlining a link between visual processing brain areas (e.g., occipital region) and the amygdala has been reported, with research demonstrating that the amygdala is involved in the early processing of stimuli in the visual cortex (de Kloet et al., 2005). In addition to the literature

demonstrating augmented amygdala activation during the processing of visual (Boubela et al., 2015; Phan et al., 2002) and salient stimuli (Davis & Whalen, 2001; Edminston et al., 2013; Liberzon et al., 2003), emotional stimuli has also been shown to increase activation in the amygdala (Costafreda et al., 2008; Stevens & Hamann, 2012).

Neuroimaging evidence is inconsistent as some studies show evidence in line with the motivational model whereas others provide support

for the negativity bias hypothesis. Hence, neuroimaging evidence for the negativity bias has been reported as unpleasant stimuli have been shown to elicit greater neural activation compared to pleasant and neutral stimuli (e.g., Falquez et al., 2016; Gehrickeet al., 2015; Keedwell et al., 2005; Siegle et al., 2002) and activation of specific brain regions associated with a negativity bias has been reported. Cunningham, Raye, and Johnson (2004) assessed brain regions involved during implicit and explicit pleasant and unpleasant

evaluations and found the right inferior frontal/insular cortex to be associated with implicit and explicit valence-based evaluations of stimuli, with this area being more activated to stimuli rated as more negative than to stimuli rated as more positive.

Further, in their landmark study, Jung et al. (2006) used positron emission tomography (PET) to identify the neuroanatomical regions selectively engaged when appetitive (pleasant stimuli) and aversive (unpleasant stimuli) processing systems are simultaneously activated. Significant activation of the right frontal pole, the left middle frontal gyrus, and left inferior frontal gyrus were revealed during the negativity bias condition which involved integrated processing of both pleasant and unpleasant stimuli. Jung et al. conducted additional analyses to identify

distinctively unique regions of activity and showed that only the middle frontal gyrus was activated during the negativity bias condition (integration of

pleasant and unpleasant information) whereas activations in the ventromedial prefrontal, limbic, and subcortical regions were associated with the processing of univalent conditions (pleasant or unpleasant information). According to Jung et al., their findings demonstrated that participants were slower to

respond and were more likely to report feeling negative (i.e., to label their subjective emotion produced by the stimuli as negative) during the negativity bias condition compared with the single valence conditions. This suggests that the processing of bivalent (both pleasant and unpleasant) stimuli requires more effort than processing of unipolar valence (pleasant or unpleasant) (Jung et al.).

Neuroimaging research allows the functional role of subcortical structures in emotion regulation and emotion regulation to be examined, however they are limited in the information they provide regarding the timing of such processes. Given that emotion processing (and negativity biases) occurs at a rapid speed and may involve both implicit and explicit processes (Cohen et al., 2016; Gyurak et al., 2011; Salmela, 2014), neuroimaging measures, in addition to behavioural and physiological measures, which have poor temporal resolution may fail to capture evidence of important but

obscured covert processes involved in emotion processing. In comparison, while limited in the amount of information available to determine the

functional role of cortical structures, event-related potentials (ERPs) are a high temporal resolution measure which enable examination of cortical responses across milliseconds and thus permit identification of both implicit and explicit attentional processes (Hajcak, Weinberg, MacNamara, & Foti, 2012; Luck, 2014).

CHAPTER 3: EVENT-RELATED POTENTIALS AND EMOTION