Do Emotional Images Improve Memory for Paired Content under Reward Conditions?
Transcript of Do Emotional Images Improve Memory for Paired Content under Reward Conditions?
Do Emotional Images Improve Memory for Paired Content under Reward Conditions?
James Laurie
Abstract Emotion increases memory for central features of emotional events. Emotional stimuli have also been observed to interfere with the processing and memory of proximate information. However, no consensus has emerged about what constitutes the central feature of an emotional event and whether different processing strategies are used for different types of emotional events. Reward has also been shown to increase performance in a memory task. Recent theories of emotion have stressed the close relationship between reward and emotion. It is surprising then, that few experiments have explored the relationship between the two during cognitive processes such as memory tasks. The present study used a word recognition task to explore whether presenting neutral words with semantically unrelated emotional images would effect memory for the words in either direction. Half the participants were incentivised with a reward to explore whether reward would increase performance in the memory task and to investigate the interaction between reward and positive affect. No significant differences were found in either condition and no interaction was observed. Results suggest that pairing neutral information with unrelated positive emotional stimuli does not increase memory for the neutral information. Results may suggest that task focus and goal priorities can eliminate the interference effects of emotional stimuli. Finally, although further is needed, results may also suggest that memory advantages for information encoded in positive emotional situations require information to be semantically or contextually related to the emotional event. Introduction Emotional events have repeatedly been shown to be remembered more and with greater clarity than neutral events. This has been shown across a wide variety of paradigms including analysis of emotional autobiographical memories (Talirico and Rubin, 2003, Talirico, et al 2009), experimentally controlled studies of episodic memory (Christianson and Loftus, 1991) and comparisons of memory for emotional versus neutral words (LaBar & Phelps, 1998; Kensinger & Corkin, 2003) and pictures (Ochsner, 2000; Hamann et al 1999) using both recognition and recall tasks. Some experiments have found evidence for Easterbrook’s (1959) cue-‐utilization hypothesis, which states that emotional arousal leads to attentional narrowing and therefore memory impairment for information presented with emotional stimuli. For instance Christianson and Loftus, (1991) found that core features of complex emotional scenes were remembered with greater clarity at the expense of peripheral information. Kensinger et al (2007) had people view either emotionally
arousing objects or emotionally neutral objects against neutral scenes. As expected, people showed greater memory for the arousing objects than the neutral objects. They showed worse memory, however, for information in the background scenes of the emotionally arousing objects than in the background scenes behind neutral objects. The emotional stimuli had appeared to impair memory for peripheral information. The emotional stroop task experimental paradigm has explored the effect of emotion on cognitive processes including attention and control. This variation of the classic stroop interference task presents participants with neutral or emotional / taboo words (i.e. kill) presented in different colours. The paradigm has consistently found that emotional words interfere with performance in the stroop task; emotional words are responded to slower and with less accuracy. (Siegrist, 1995, Whalen et al., 1998,). However, while negative emotional states have been shown to narrow attention on the source of arousal, positive emotional states have been shown to broaden processing and increase creativity (Fredrickson, 2001). Furthermore, participants are not passive responders to stimuli as Eastebrook’s (1958) cue utilisation hypothesis suggests, particularly if they are given a goal to prioritise, such as the task of memorizing words. Easterbrook limits behavior to an automatic response to the source of arousal. By contrast, Levine and Edelstien, 2010 offers a more nuanced consideration of the effects of emotion on memory that allows for a complex interaction between top-‐down processing of goal-‐relevant information and bottom-‐up stimulus-‐response. Other studies have found evidence for memory enhancement of incidental, peripheral and proximate information of emotional scenes. For instance, Libkuman et al 1990 found that memory for both central and irrelevant, peripheral aspects of a scene was enhanced during emotional arousal. Information that is temporarily proximate has been shown to receive processing priority: A study by Anderson et al (2006) found that memory for neutral pictures was enhanced if they were presented temporarily immediately prior or immediately after unrelated arousing emotional images. Mather and Nesmith (2008) demonstrated that spatial information for emotional stimuli is prioritized in processing. They found that participants demonstrated increased memory for the location of affective and arousing pictures presented on a computer screen when compared with neutral pictures. Doerksen and Shimamura (2001) found a memory advantage for the colour of previously presented affective words over neutral words. Information that is contextually and semantically relevant to the emotional aspect of the scene also appears to receive priority in processing for memory. This includes both semantic context and social context. For instance, studies by Brierley et al (2007) and Guillet & Arndt (2010) found that non-‐target words embedded in sentences with emotional target words were remembered more than the non-‐target words embedded in otherwise matched neutral sentences. Increased memory for peripheral information is also found where that information is processed social
contexts. Studies by Tsukiura & Cabezaa (2008) and Bridge et al (2010) demonstrated that the retrieval of face-‐name associations was more accurate and faster for smiling than neutral faces. The above studies show evidence that neutral information processed in semantic, temporal or spatial proximity to an emotional stimuli can be remembered more; simply by virtue of its proximity to the emotional event. According to Priority Binding Theory (see esp. Mackay et al 2004 and Mather 2007), we bind congruent information together using semantic, phonetic and visual cues to create a cohesive memory. Memories often form when there is a strong semantic or contexual association (i.e. table-‐chair or bread-‐eat) between the emotional target stimuli and the incidental information that provides a possibility for binding information to the emotional event (Medford et al, ). Previous studies have shown that during negative emotional events, there can be a memory advantage for information that is encoded in spatial or temporal proximity but that is not semantically or contexually related to the emotional event (Libkuman et al, 1999; Anderson et al 2006). However, to our knowledge, this has never been demonstrated under experimental conditions for information encoded in positive emotional contexts. Therefore the current study sought to investigate whether there would be a difference in memory recognition between words presented with positive emotional pictures and neutral emotional pictures. The current study paired neutral words with semantically and contextually unrelated pictures. Therefore, if there is an increase in recognition memory for words presented with positive emotional pictures over neutral pictures, this may suggest that there is a memory advantage for information encoded in spatial and temporal proximity to positive emotional events. Alternatively, if there is a decrease in recognition memory for words presented with positive emotional pictures, this would suggest that the positive emotional stimuli is interfering with the processing of the target information. Previous studies have shown that reward incentives increase performance in memory tasks for pictures (Adcock et al, 2006, Whittman et al, 2005), location (Kawagoe et al, 1998), words (Madan and Spetch, 2012) and complex semantic information (Marayame & Kuhbandner, 2011). Neuroimaging studies have demonstrated that reward incentives increase memory through activation of both lateral prefrontal areas that are implicated in cognitive control (Watanabe, 1996, Leon & Shadlen, 1999) and dopamine pathways (Berridge, 2007). Reward and positive affective states are so closely related that a number of theorists suggest that they are entirely indistinguishable. For instance, Rolls (2000) argues that positive emotion is a bodily experience of the anticipation or attainment of goals and negative emotion is the bodily experience of the avoidance of threat. It is surprising then, that few experiments have sought to investigate the interaction between reward and positive effect on cognitive functions such as memory. Two recent, previous studies have explored the interaction of emotion and reward on memory encoding. Whitmann et al (2008) compared memory for positive emotional stimuli with neutral emotional stimuli under reward incentive. They
found an interaction between the two variables; reward enhanced memory significantly more in the positive emotion condition than in the neutral emotion condition. However, in this experiment, participants were not instructed to remember the stimuli, so encoding was incidental and secondly, the reward incentive was not related to memory encoding but to performance in an immediately ensuing number comparison task. A second study by Shigemune et al (2010) compared memory for negative emotional stimuli with neutral emotional stimuli under reward incentive. As expected, they found that negative affective stimuli were remembered better than neutral stimuli and that reward increased memory for both negative and neutral stimuli in equal measures, i.e. there was no interaction between reward and negative stimuli. Therefore the present study sought to explore whether participants incentivized with reward would perform better in a recognition task. Secondly, if there is a memory advantage for incidental information that is encoded in a positive emotional or neutral context, would reward have an additive effect on memory improvement in either condition? Unlike Whitmann et al (2008), in this study reward was related to success in the memory task and participants were instructed to remember target items, so encoding was intentional. Thirdly, if there is a memory disadvantage for incidental information encoded in a positive emotional context (i.e. if emotional stimuli interfered with memory encoding for proximate information), would reward reduce the interference effect through an increase in goal motivation and, therefore, an increase in task focus? Method Design A mixed factorial design was used to investigate the effect of emotional context and reward on memory for target words. Specifically, the experiment explored whether pairing neutral words with emotional images would have an effect on performance in a recognition task for the words and whether promise of reward would increase performance in the task. The dependent variable was recognition memory, measured by number of target words correctly identified in a recognition task. The independent variables were emotional context and reward. The within-‐subjects factor was emotional context, with two levels; words presented with neutral images and words presented with positive images. The between-‐subjects factor was reward, with two levels; reward and non-‐reward. This was manipulated by incentivising the reward group during the experiment instructions. The experiment was conducted using a web-‐based application that presented 50 randomly ordered and randomly paired compound stimuli: neutral target words presented centrally in front of either positive emotional images or neutral images. Following a maths distractor task, participants completed a yes/no/uncertain recognition task to test memory for target words.
Participants 107 participants (57 females and 50 males) took part in the experiment. This was a convenience sample taken from colleagues, extended friends and family of the researchers, recruited through email and personal invitation to take part in a ‘memory experiment’. Previous studies have shown a progressive decline in memory function with ageing (Castel et al 2002 & Hedden & Gabrielii, 2004). A study by Warring & Kesinger (2009) also revealed that adults over the age of 50 show decreased interference effect of arousing stimuli in memory tasks. Therefore, recruitment selection ensured that all participants were between the age of 20 and 50. Before the task, participants had to complete an online form that required an entry for age. Participants could not progress to the experiment unless they were between 20 and 50. Further control for age was achieved through the application counterbalancing the groups for age across a median split. Mean age was 33.76 with a range of 21-‐50 and a standard deviation of 6.81. Recruited participants all spoke English to a high level of fluency. Following the completion of the experiment, box plots were used to analyse the data-‐sets to look for outliers in false positive scores. Unusually high false positive scores would suggest the participant had either guessed responses or had a very poor memory. Materials / Stimuli 25 neutral and 25 positive pictures were selected from the International Affective Picture System, a selection of a standardised images developed by Lang et al (2005). The pictures have been previously rated on a 10-‐point scale for both arousal and valence. Neutral condition pictures had a mean valence of 5.07, SD = 0.34 and mean arousal of 2.97, SD = 1.06. Positive condition pictures had a mean valence was 8.3, SD = 0.76 and arousal rating of 4.52, SD = 1.34. T-‐tests revealed significant differences between valence t(48) = 19.83, p<0.001 and arousal t(48) = 3.02, p=0.007. 100 neutral words were selected from Affective Norms for English Words -‐ ANEW (Bradley and Lang, 1999). The mean valence for the words was 4.98, SD = 0.17. In each trial, 25 words were randomly assigned by the application to be presented with positive pictures and 25 words with the neutral pictures. A further 50 words were presented in random order with these 50 target words in a subsequent recognition task. Reward was manipulated by embedding within the task instructions a promise of reward (entry into a £50 prize draw) for high performance (a score >50%). Care was taken to control for semantic context, which has been shown to increase levels of
processing and improve performance in a recall task (i.e. Craik & Lockhart, 1972). Associations between words and pictures were checked separately by all researchers so that no word represented any object presented in any of the pictures. Furthermore, the application randomly associated words and pictures across participants. Procedure The experiment was presented as a web-‐based application accessed at http://picturewords.herokuapp.com. An initial instruction page informed participants that the experiment investigates visual memory, that data would be collected anonymously and used confidentially and that they could retract their data by leaving the webpage before completion of the experiment. Participants were asked to ensure they were in a quiet environment without distraction and had a good connection to the web. Participants then had to complete a web form that recorded age (20 -‐ 50) and gender (M or F). Consent was gained using a click box, which bought participants onto the instruction page. Participants were instructed that they would be shown a series of images and words and their task was to remember the words, as they would later be asked to identify them from a list. The reward group were here informed of a reward and told that they could submit their email address at the end of the experiment. Immediately after, a screen was presented for 5 seconds with the words ‘please focus on the fixation cross’. A fixation cross was presented concurrently, 50 pixels below the centre of the screen. Following this, 50 neutral words were consecutively presented with 25 neutral pictures and 25 positive pictures. Each randomly-‐paired stimuli were presented for 3 seconds. A crosshair was presented for 1 second between stimuli, 50 pixels below the centre of the screen. Words were presented 50 pixels below the centre of the screen, in white, against a black background, in front of the picture (see fig 1). This was to ensure that the words were centrally presented but did not obscure key information in the pictures. Following presentation of stimuli, participants completed eight simple arithmetic problems. This was a distractor task to control for recency effect and to ensure that words were not retained in working memory. Participants were then presented with a second instruction page, which informed participants that they would be shown a series of 100 words. They were informed that they should press "Y" if the word appeared in the previous task, ‘N’ if the word did not appear and “U” if they were uncertain. At this stage, those assigned to the reward group were once again reminded about the reward. Words were presented in the middle of the screen, with the above instructions directly underneath (see fig 2). Pressing either the ‘Y’, ‘N’ or ‘U’ key initiated a
progression to the next word. A progress bar ran across the bottom of the screen, so that participants could chart their progress. Following the randomly ordered presentation of all 50 target words and 50 novel neutral words, participants were thanked for taking part and reminded of the anonymity of the data collection. A participant number was presented and participants were informed that they could retract their data by sending an email with their participant number to a given email address. Finally, those in the reward group were asked to enter their email address in a web form, if they wished to enter the £50 prize draw. Results Following analysis of error-‐rates using boxplots, participants who scored outside the 95% confidence interval were removed from the final analysis. This resulted in the removal of the data of 5 participants, leaving 102 participants in the dataset. A repeated measures ANOVA was conducted to compare the effect of two different interventions, (emotional context and reward) on performance in a word recognition task. Results are presented in plot 1. There was no significant main effect of emotional context / picture category on the number of words recognised, F(1,102)=0.773, p=0.381, with no difference between the mean number of words recalled in the positive images condition (M=14.87, SD=0.3) and the neutral images condition (M=14.32, SD=0.3. This suggests that pairing neutral words with emotional images has no effect on memory for the neutral words. There was no significant effect of reward on the number of words correctly recognised, F(1,102)=1.603, p=0.208. Although results fall outside of significance, they fall in the expected direction. The mean number of words recalled in the reward condition was 13.9, SD=0.40. The mean number of words recalled in the reward condition was 15.3. SD=0.39. However, the lack of significance suggests that promise of reward had no impact on performance in the memory task. There was also no significant interaction between the picture conditions and the reward condition. F(1,102) = 0.437, p=0.510. This indicates that emotional valence does not mediate the effect of reward. Further analysis of the data was conducted in order to control for participant’s response bias and task accuracy. Scores were standardised as z-‐scores, then accuracy was indexed by calculating hit rates minus false alarms which converted scores to d’. However, results still remained insignificant for each variable and their interaction. Discussion
No significant differences were found at test between recognition scores for words presented with positive or neutral stimuli. Memory for words presented with emotional stimuli was not impaired, in comparison with words presented with neutral stimuli. Therefore, the emotional stimuli presented with the target word did not interfere with the processing of their compound words. The lack of significance in the experiment results may be due to an artifact of the experiment design or it may point to some more interesting suggestions for further research. Firstly, it is possible that the pictures themselves were not sufficient to induce an affective response. Although these photographs have been previously standardized, many were taken over 20 years ago, so they may have lost cultural relevance and therefore their ability to induce affective changes. There is also evidence that effects of emotion on memory increase with time (LaBar & Phelps, 1998). It is possible that our manipulation would have become more evident if the task-‐test interval was increased. It is also possible that our simple yes/no/uncertain recognition test design was not sensitive enough to detect the differences between memory for neutral information presented with emotional and neutral images. Previous experiments have found that emotional stimuli interfere with cognitive processing (Whalen et al., 1998, Kensinger et al 2007,). There may be a number of reasons why the present study did not find this effect. Results may indicate that participants were able to focus on the task and avoid distraction by the emotional stimulus. This outcome may be seen as a confirmation of goal-‐relevant theories of emotional memory processing (Levine & Edelstein, 2010) over against Easterbrook’s (1958) Cue Utilisation hypothesis: Participants did not automatically respond to the presence of the emotional stimuli but were able eliminate the bottom-‐up stimulus-‐response effect of the pictures and continue with top-‐down task-‐ oriented memory encoding. Experiments using the emotional stroop task (Whalen et al 1998) have found that clinical populations such as frontal lobe patients exhibit much lower thresholds for emotional interference (Bar-‐Haim et al 2007). It may be possible that a comparison with clinical populations against the general population sample used in this study may reveal interference effects of emotional stimuli on memory encoding. Previous experiments that found an increase in memory encoding for neutral information in proximity to emotion stimuli. However, these experiments have either maintained a semantic / contextual link between the neutral information and the emotional event (for instance words presented in emotional sentences -‐ Brierley et al, 2007 and Guillet & Arndt, 2010) or have presented the information alongside arousing, negative affective stimuli (Libkuman et al 1990). In the present study design, care was taken to ensure that words were not semantically related to the pictures and the pictures were positive, rather than negative and arousing. Results may suggest that for emotional events to increase memory for proximate information, the information needs to be contextually or
semantically related to the event and / or needs to be placed proximately to highly arousing, negative stimuli. In order to explore this further, the present study could be repeated with two further conditions: neutral words presented with semantically related emotional pictures (i.e. the word ‘bottle’ with a picture of a baby) and neutral words presented with arousing, negative images. We may hypothesize that neutral words presented in the ‘semantically-‐related’ condition will be better remembered than words presented with semantically unrelated pictures. This is likely to occur because the contextual / semantic relationship between the stimuli allows the word to be bound with the emotional event, enabling the memory advantage for the words, seen in other experiments. Secondly, we may hypothesize that words presented in the ‘negative arousing’ condition will be remembered better than words presented with semantically unrelated positive images. Maratos et al (2001) used fMRI to investigate the different areas of the brain involved in processing information encoded in positive affective and neutral affective states. They found that information encoded in negative emotional states was associated with activity in the right dorsolateral prefrontal cortex as well as activity in limbic areas such as the amygdala and hippocampus. By contrast, information encoded during positive emotional states was associated with activity in bilateral frontal and orbitofrontal areas, with less activity in limbic areas. This may provide evidence for the idea, suggested by Levine and Burgess, (1997) and Levine and Pizarro (2004) that different information processing strategies are associated with different affective events. Learning through positive emotion requires semantic associations to be established, or at least that positive emotions facilitate connective thinking and assimilation of information to current schema information networks. In contrast, learning through negative emotions does not necessarily need semantic associations; temporal and spatial proximity is sufficient to improve memory encoding (see Doerksen and Shimamura (2001) & Anderson et al (2006). These two different information and memory encoding strategies have obvious evolutionary benefits. During positive emotional experiences we broaden our thinking to seek out associations between the positive affect and environment. Once these semantic associations are established, they can be encoded into memory. If they are not found, peripheral information is discarded. However, in order to survive threats, early primates needed to respond to the widest possible source of danger. Therefore anything associated with the source of threat may be encoded alongside it in memory. Further studies are needed to explore this idea; particularly those that investigate what type of information is encoded in memory during different affective states. No significant differences were found between the reward and the non-‐reward group. In light of overwhelming previous evidence for the effect of reward on memory tasks (Adcock et al, 2006, Whittman et al, 2005), it is probable that our
intervention failed to incentivise those in the reward group. There are a number of possible reasons for this, including participants calculating that it is unlikely that they would win the reward. Alternatively, it may be that because all participants volunteered to take part, this altruistic act in itself was enough of a reward for both conditions, that the intervention itself failed to have any additive effect. Finally, most previous experiments that have found significant effects for reward have used a within groups design for reward. For instance (Shigemune et al 2010) presented a ‘reward indicator’ before a reward stimuli is presented, so that the difference between a reward stimulus and a non-‐reward stimulus was constantly reinforced. Finally there was no observed interaction between reward and emotional context. Reward was not observed to have an additive effect on memory ability for information encoded in either positive or neutral conditions, despite the intentionality of the encoding and the association between the task and the reward incentive. As there was no memory disadvantage for incidental information encoded in a positive emotional context results did not confirm whether reward incentives would reduce the interference effect of emotional stimuli. In order to explore this further, we would need to ensure that our reward intervention was effective. Secondly, it would probably be more effective to explore the reward / affect interaction by comparing memory for emotional pictures versus neutral pictures, rather than testing information encoded in proximity to emotional pictures, as occurred during the present experiment. To conclude, the current study found that by placing neutral affective words with positive images neither increased nor decreased performance in a subsequent word memory task. The study also found no effect of a reward intervention on performance in the recognition task or an interaction between the variables. Results may be due to experimental artifacts, may indicate that task orientation mediates the effect of emotional interference or may indicate that positive emotional contexts only have an additive effect on memory when the information can be bound with the emotional event through contextual, semantic or pragmatic associations. However, this final conclusion is tentative and requires further investigation.
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Appendix Fig 1. Compound Stimuli Example
Fig 2. Recognition Test Example
Butter
Was this word included in task 1?
Press ‘Y’, ‘N’ or ‘U’.