Distinct brain systems underlie the processing of valence and arousal of affective pictures

Valence and arousal are thought to be the primary dimensions of human emotion. However, the degree to which valence and arousal interact in determining brain responses to emotional pictures is still elusive. This functional MRI study aimed to delineate neural systems responding to valence and arousal, and their interaction. We measured neural activation in healthy females (N = 23) to affective pictures using a 2 (Valence) × 2 (Arousal) design. Results show that arousal was preferentially processed by middle temporal gyrus, hippocampus and ventrolateral prefrontal cortex. Regions responding to negative valence included visual and lateral prefrontal regions, positive valence activated middle temporal and orbitofrontal areas. Importantly, distinct arousal-by-valence interactions were present in anterior insula (negative pictures), and in occipital cortex, parahippocampal gyrus and posterior cingulate (positive pictures). These data demonstrate that the brain not only differentiates between valence and arousal but also responds to specific combinations of these two, thereby highlighting the sophisticated nature of emotion processing in (female) human subjects.     

Accelerative and decelerative effects of hedonic valence and emotional arousal during visual scene processing

Perceptual processing of natural scene pictures is enhanced when the scene conveys emotional content. Such “motivated attention” to pleasant and unpleasant pictures has been shown to improve identification accuracy in non-speeded behavioural tasks. An open question is whether emotional content also modulates the speed of visual scene processing. In the present studies we show that unpleasant content reliably slowed two-choice categorization of pictures, irrespective of physical image properties, perceptual complexity, and categorization instructions. Conversely, pleasant content did not slow or even accelerated choice reactions, relative to neutral scenes. As indicated by lateralized readiness potentials, these effects occurred at cognitive processing rather than motor preparation/execution stages. Specifically, analysis of event-related potentials showed a prolongation of early scene discrimination for stimuli perceived as emotionally arousing, regardless of valence, and reflected in delayed peaks of the N1 component. In contrast, the timing of other processing steps, reflected in the P2 and late positive potential components and presumably related to post-discriminatory processes such as stimulus–response mapping, appeared to be determined by hedonic valence, with more pleasant scenes eliciting faster processing. Consistent with this model, varying arousal (low/high) within the emotional categories mediated the effects of valence on choice reaction speed. Functionally, arousal may prolong stimulus analysis in order to prevent erroneous and potentially harmful decisions. Pleasantness may act as a safety signal allowing rapid initiation of overt responses.     

Emotional valence and arousal effects on memory and hemispheric asymmetries

This study examined predictions based upon the right hemisphere (RH) model, the valence–arousal model, and a recently proposed integrated model (Killgore & Yurgelun-Todd, 2007) of emotion processing by testing immediate recall and recognition memory for positive, negative, and neutral verbal stimuli among 35 right-handed women. Building upon methodologies of previous studies, we found that words presented to the right visual field/left hemisphere (RVF/LH) were recalled and recognized more accurately than words presented to the left visual field/right hemisphere (LVF/RH), and we found significant valence by visual field interactions. Some findings were consistent with one of the models evaluated whereas others were consistent with none of the models evaluated. Our findings suggest that an integration of the RH and valence–arousal models may best account for the findings with regard to hemispheric lateralization of memory for emotional stimuli.     

Changing the focus of attention: The interacting effect of valence and arousal

We examined how valence and arousal of an image influence visual attention. “Spotlight of attention” theory suggests that positive affect broadens, and negative affect narrows, one's aperture of attention, whereas the arousal theory literature suggests that arousal level is what modulates attentional focus, with highly arousing affect capturing attention, regardless of valence. In two experiments, a digit parity task was used to index the influence of valence, and arousal, on visual attention. Positive or negative images were displayed centrally on each trial, with single digits presented more peripherally (Experiment 1) or more centrally (Experiment 2) to the image. In both Experiments participants were slower, and less accurate at making parity decisions (e.g., both digits odd or both even) when the image was negative relative to positive, and of high arousal. For low arousal images, positive, relative to negative, valence images led to greater impairment of the digit parity task. Findings suggest that arousal level of images modulates the influence of valence on distribution of visual attention. Highly negative emotional images may command or capture attention, but there are other factors that can lead to attention capture, even in low arousing positive stimuli.     

Alteration of expected hemispheric asymmetries: valence and arousal effects in neuropsychological models of emotion

The relative advantage of the left (LH) over the right hemisphere (RH) in processing of verbal material for most individuals is well established. Nevertheless, several studies have reported the ability of positively and negatively valenced stimuli to enhance and reverse, respectively, the usual LH>RH asymmetry. These studies, however, have used baseline stimuli that differed from emotional stimuli on two dimensions (i.e., valence and verbal/nonverbal nature), creating interpretive difficulties as to whether differences across these conditions are due to differences in valence or the verbal/nonverbal nature of the primes used in the baseline condition. In addition, these studies, along with many others in the literature, have failed to control for potential confounding effects of arousal. Emotional stimuli vary on dimensions of valence as well as arousal and arousal may be asymmetrically presented in the brain therefore contributing to observed asymmetries. Taken together, these considerations underscore the importance of controlling for both valence as well as arousal in any investigation of the effects of emotional stimuli. The objectives of the present study were twofold: (1) to employ an appropriate baseline condition to render emotional stimuli vs. baseline stimuli comparisons meaningful and (2) to examine the extent to which emotional verbal stimuli, equated for arousal level, alter the expected LH>RH asymmetry in a consonant trigram task. Results demonstrated that when LH lateralized consonant trigram presentations were preceded by a positive prime, an enhancement of the expected LH>RH asymmetry was observed. In contrast, when trigram presentations lateralized to the RH were preceded by a negative prime, a complete reversal of the typical asymmetry was found with RH>LH performance. These results are analogous to the pattern of relative hemispheric activations observed for various mood states. Controlling for arousal in studies investigating asymmetries associated with emotional processing may allow more clear interpretation of data intended to test predictions of neuropsychological models of emotion. Moreover, equating stimuli on the dimension of arousal as well as valence may shed more light on conflicting findings with regard to perception vs. expression of emotion.     

Developmental reversals in false memory: Effects of emotional valence and arousal

Do the emotional valence and arousal of events distort children’s memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can be manipulated factorially. False memories increased with age for unpresented semantic associates of word lists, and net accuracy (the ratio of true memory to total memory) decreased with age. These surprising developmental trends were more pronounced for negatively valenced materials than for positively valenced materials, they were more pronounced for high-arousal materials than for low-arousal materials, and developmental increases in the effects of arousal were small in comparison with developmental increases in the effects of valence. These findings have ramifications for legal applications of false memory research; materials that share the emotional hallmark of crimes (events that are negatively valenced and arousing) produced the largest age increases in false memory and the largest age declines in net accuracy.     

Reproducing affective norms with lexical co-occurrence statistics: Predicting valence,arousal, and dominance

Human ratings of valence, arousal, and dominance are frequently used to study the cognitive mechanisms of emotional attention, word recognition, and numerous other phenomena in which emotions are hypothesized to play an important role. Collecting such norms from human raters is expensive and time consuming. As a result, affective norms are available for only a small number of English words, are not available for proper nouns in English, and are sparse in other languages. This paper investigated whether affective ratings can be predicted from length, contextual diversity, co-occurrences with words of known valence, and orthographic similarity to words of known valence, providing an algorithm for estimating affective ratings for larger and different datasets. Our bootstrapped ratings achieved correlations with human ratings on valence, arousal, and dominance that are on par with previously reported correlations across gender, age, education and language boundaries. We release these bootstrapped norms for 23,495 English words.     

Emotion and memory: A recognition advantage for positive and negative words independent of arousal

Much evidence indicates that emotion enhances memory, but the precise effects of the two primary factors of arousal and valence remain at issue. Moreover, the current knowledge of emotional memory enhancement is based mostly on small samples of extremely emotive stimuli presented in unnaturally high proportions without adequate affective, lexical, and semantic controls. To investigate how emotion affects memory under conditions of natural variation, we tested whether arousal and valence predicted recognition memory for over 2500 words that were not sampled for their emotionality, and we controlled a large variety of lexical and semantic factors. Both negative and positive stimuli were remembered better than neutral stimuli, whether arousing or calming. Arousal failed to predict recognition memory, either independently or interactively with valence. Results support models that posit a facilitative role of valence in memory. This study also highlights the importance of stimulus controls and experimental designs in research on emotional memory.     

Avoid violence,rioting, and outrage; approach celebration,delight, and strength: Using large text corpora to compute valence,arousal, and the basic emotions

Ever since Aristotle discussed the issue in Book II of his Rhetoric, humans have attempted to identify a set of “basic emotion labels”. In this paper we propose an algorithmic method for evaluating sets of basic emotion labels that relies upon computed co-occurrence distances between words in a 12.7-billion-word corpus of unselected text from USENET discussion groups. Our method uses the relationship between human arousal and valence ratings collected for a large list of words, and the co-occurrence similarity between each word and emotion labels. We assess how well the words in each of 12 emotion label sets—proposed by various researchers over the past 118 years—predict the arousal and valence ratings on a test and validation dataset, each consisting of over 5970 items. We also assess how well these emotion labels predict lexical decision residuals (LDRTs), after co-varying out the effects attributable to basic lexical predictors. We then demonstrate a generalization of our method to determine the most predictive “basic” emotion labels from among all of the putative models of basic emotion that we considered. As well as contributing empirical data towards the development of a more rigorous definition of basic emotions, our method makes it possible to derive principled computational estimates of emotionality—specifically, of arousal and valence—for all words in the language.     

Emotion words, regardless of polarity, have a processing advantage over neutral words

Despite increasing interest in the interface between emotion and cognition, the role of emotion in cognitive tasks is unclear. According to one hypothesis, negative valence is more relevant for survival and is associated with a general slowdown of the processing of stimuli, due to a defense mechanism that freezes activity in the face of threat. According to a different hypothesis which does not posit a privileged role for the aversive system, valence, regardless of polarity, facilitates processing due to the relevance of both negative and positive stimuli for survival and for the attainment of goals. Here, we present evidence that emotional valence has an overall facilitatory role in the processing of verbal stimuli, providing support for the latter hypothesis. We found no asymmetry between negative and positive words and suggest that previous findings of such an asymmetry can be attributed to failure to control for a number of critical lexical variables and to a sampling bias.     

Mood and the DRM paradigm: An investigation of the effects of valence and arousal on false memory

Recent studies regarding the effect of mood on the DRM (Deese–Roediger–McDermott) illusion have not been able to clearly establish yet whether valence or arousal is most critical in determining susceptibility to false memories, nor what the underlying processes are. In three experiments, both the valence and the level of arousal of participants' mood were manipulated. Six conditions were used: positive mood with high/low arousal, negative mood with high/low arousal, neutral mood, and a control condition. Memory was tested by means of immediate and delayed recognition and immediate free recall. The mood induction procedure was effective. For recognition memory, there was an effect of arousal on the endorsement of critical lures. Low-arousal moods elicited more false recognition than high-arousal moods, regardless of valence. Based on signal detection analyses, the effect was attributed to more liberal response criteria with low arousal, in combination with a tendency towards improved item-specific memory with high arousal.     

Brightness differences influence the evaluation of affective pictures

We explored the possibility of a general brightness bias: brighter pictures are evaluated more positively, while darker pictures are evaluated more negatively. In Study 1 we found that positive pictures are brighter than negative pictures in two affective picture databases (the IAPS and the GAPED). Study 2 revealed that because researchers select affective pictures on the extremity of their affective rating without controlling for brightness differences, pictures used in positive conditions of experiments were on average brighter than those used in negative conditions. Going beyond correlational support for our hypothesis, Studies 3 and 4 showed that brighter versions of neutral pictures were evaluated more positively than darker versions of the same picture. Study 5 revealed that people categorised positive words more quickly than negative words after a bright picture prime, and vice versa for negative pictures. Together, these studies provide strong support for the hypotheses that picture brightness influences evaluations.     

Switching between sensory and affective systems incurs processing costs

Recent models of the conceptual system hold that concepts are grounded in simulations of actual experiences with instances of those concepts in sensory-motor systems (e.g., Barsalou, 1999, 2003; Solomon & Barsalou, 2001). Studies supportive of such a viewhave shown that verifying a property of a concept in one modality, and then switching to verify a property of a different concept in a different modality generates temporal processing costs similar to the cost of switching modalities in perception. In addition to non-emotional concepts, the present experiment investigated switching costs in verifying properties of positive and negative (emotional) concepts. Properties of emotional concepts were taken from vision, audition, and the affective system. Parallel to switching costs in neutral concepts, the study showed that for positive and negative concepts, verifying properties from different modalities produced processing costs such that reaction times were longer and error rates were higher. Importantly, this effect was observed when switching from the affective system to sensory modalities, and vice-versa. These results support the embodied cognition view of emotion in humans.     

The content and structure of laypeople's concept of pleasure

Five studies were conducted to map the content and structure of laypeople's conceptions of pleasure. Instances of the pleasure concept collected in Study 1 consisted predominantly of objects, events or persons described as sources of pleasure. Content analysis suggested that the pleasure category, like emotional response categories, might be formed at an implicit level where various pleasure antecedents are grouped based on common phenomenological qualities of the affective experience. Studies 2 and 3a showed that the pleasure category possesses a graded structure and fuzzy boundaries. Results further revealed that, either when explicitly presented with labels (Study 3b) or left to their own implicit categories during a sorting task (Study 4), laypeople represented pleasure as a hierarchical concept in which differentiated pleasure types (i.e., intellectual, emotional, social and physical) were subsumed under a higher level unitary form of pleasure. In this structure, unitary and differentiated pleasures shared a set of common affective qualities but were also distinguishable by unique and distinctive affective characteristics (Study 5). Ties to prior theories of pleasure and implications for decision making and behavioural research are discussed.     

Age differences in affective forecasting and experienced emotion surrounding the 2008 US presidential election

In everyday life, people frequently make decisions based on tacit or explicit forecasts about the emotional consequences associated with the possible choices. We investigated age differences in such forecasts and their accuracy by surveying voters about their expected and, subsequently, their actual emotional responses to the 2008 US presidential election. A sample of 762 Democratic and Republican voters aged 20 to 80 years participated in a web-based study; 346 could be re-contacted two days after the election. Older adults forecasted lower increases in high-arousal emotions (e.g., excitement after winning; anger after losing) and larger increases in low-arousal emotions (e.g., sluggishness after losing) than younger adults. Age differences in actual responses to the election were consistent with forecasts, albeit less pervasive. Additionally, among supporters of the winning candidate, but not among supporters of the losing candidate, forecasting accuracy was enhanced with age, suggesting a positivity effect in affective forecasting. These results add to emerging findings about the role of valence and arousal in emotional ageing and demonstrate age differences in affective forecasting about a real-world event with an emotionally charged outcome.     

The affective interval: An investigation of the peaks and valleys during high- and moderate-intensity interval exercise in regular exercisers

Evidence supports the notion that people generally feel worse during high(er) intensity exercise but experience an affective rebound immediately following cessation that often exceeds pre-exercise feeling states. Considering rest/recovery is an integral part of interval exercise, it is of interest to determine the degree of affective reactivity and recovery that may occur during interval exercise of different intensities. The purpose of the present study was to examine affective reactivity to and recovery from an acute bout of moderate-intensity (MIIE) and high-intensity interval exercise (HIIE). Participants (N = 25, 13 females, 23.3 ± 4.0 yrs, BMI = 25.7 ± 4.1 kg m⁻²) completed 4 sessions at the same time of day with at least 24-h between each session: a baseline session to record resting affect, a graded exercise test on a stationary bike (cycle ramp protocol 25 W·min-1) to volitional exhaustion, and then completed a high- (HIIE) and moderate-intensity interval exercise (MIIE) session where affect was recorded prior to, during, and up to 30-min post exercise. Participants reported more negative feeling states during the HIIE session compared to the MIIE session, but these states recovered similarly as early as 5-min post-exercise. In addition, while affective change (reactivity and rebounds) were relatively equal during the MIIE, declines in affect during the HIIE outweighed the affective rebounds associated with rest, resulting in a large decline in affective state from pre-exercise.     

The effect of pain and the anticipation of pain on temporal perception: A role for attention and arousal

The overestimation of the duration of fear-inducing stimuli relative to neutral stimuli is a robust finding within the temporal perception literature. Whilst this effect is consistently reported with auditory and visual stimuli, there has been little examination of whether it can be replicated using painful stimulation. The aim of the current study was, therefore, to explore how pain and the anticipation of pain affected perceived duration of time. A modified verbal estimation paradigm was developed in which participants estimated the duration of shapes previously conditioned to be associated with pain, compared to those not associated with pain. Duration estimates were significantly longer on trials in which pain was received or anticipated than on control trials. Slope and intercept analysis revealed that the anticipation of pain resulted in steeper slopes and greater intercept values than for control trials. The results suggest that increased arousal and attention, when anticipating and experiencing pain, result in longer perceived durations. The results are discussed in relation to internal clock theory and neurocognitive models of time perception.     

Human content in affect-inducing stimuli: A secondary analysis of the international affective picture system

We report a secondary analysis of the international affective picture system (IAPS), the broadest available standardized sample of emotional stimuli, which confirmed our prediction that the distribution of slides across the valence and arousal dimensions would be related to human versus inanimate slide content. Pictures depicting humans are over-represented in the high arousal/positive and high arousal/negative areas of affective space as compared to inanimate pictures, which are especially frequent in the low arousal/neutral valence area. Results pertaining to dominance ratings and gender differences in valence and arousal ratings further suggest that there are qualitative differences between emotional reactions to animal or human slide content and responses to nonsocial still photos. Researchers need to be mindful of this distinction when selecting affect-inducing stimuli.

Individual differences in the relationship between pleasure and arousal

The two fundamental dimensions assumed to underlie emotional experience—pleasure and arousal—are considered to be independent across individuals. We present evidence from an experience sampling study demonstrating that this independence does not necessarily hold when considering the affective experiences of a single individual. Participants (N = 80) reported how they were feeling in terms of pleasure and arousal nine times a day for seven days. The data showed that, although on average pleasure and arousal were independent, within-person pleasure–arousal associations substantially varied and ranged from strongly positive to strongly negative. This finding demonstrates that pleasant/unpleasant feelings usually co-occur with high arousal for some (reflecting joy/stress), but with low arousal for others (reflecting relaxation/sadness) and that persons differ in whether arousal is usually pleasant or unpleasant. These differences were found to be related to dispositional reward responsiveness, with high reward responsive individuals being characterized by a positive relation between pleasure and arousal and vice versa.