The Acquisition of Avoidance Tendencies towards Conditioned Fear Cues
Darleen Lobo 0373141
Universiteit van Amsterdam Master these
Abstract
We investigated how approach-avoidance tendencies towards conditioned fear cues are acquired. Participants underwent a differential Pavlovian fear conditioning procedure, during which the picture of an initially neutral cue (e.g., a cube; CS+) was always followed by a loud noise (US) whereas the picture of another initially neutral cue (e.g., a cylinder; CS-) was never followed by the US. Participants were asked to learn when to expect the US (CS-US contingency) while standing on a Nintendo WII Balance Board that measured their center of pressure (COP). Changes in the COP were used as a measurement of approach-avoidance tendencies. After the conditioning phase, a symbolic approach-avoidance task (AAT) was administered during which participants were instructed to move a virtual manikin onscreen towards or away from the CSs. Reaction times for approaching or avoiding each CS were measured and also served as measures for action tendencies, making it possible to compare the action tendencies measured during fear conditioning to the ones measured after fear conditioning. Results showed no significant effects of the stimuli on changes in the COP and no significant effects on the SRCT indicating that no measurable avoidance tendencies were acquired during the fear conditioning procedure. The present study may contribute to
Introduction
What happens when we avoid a situation or cue? If the situation or cue is physically threatening, like a burning building, or socially threatening, like conflict with a co-worker, avoiding it is most probably adaptive and useful (Lovibond, 2006). But if a situation or cue is not genuinely threatening, like a controlled bonfire or a difference of opinion with a co-worker, excessive avoidance can be maladaptive and harmful. Excessive avoidance can play an integral part in maintaining pathological anxiety by preventing individuals from
experiencing what would happen if they didn’t avoid the cue or situation (Barlow, 2002; Declercq, De Houwer & Baeyens, 2008; Lovibond et al, 2009). For example, avoiding office parties out of fear of being ridiculed in social groups will most probably never lead to
positive experiences within social groups. This could result in the individual never learning that social situations are not necessarily embarrassing and, accordingly, the maintenance of the fearful feelings towards interacting in social groups. Understanding how avoidance is acquired could lead to new insights on the role avoidance plays in pathological anxiety.
There are many theoretical models of avoidance learning (see Krypotos, Effting, Kindt & Beckers, 2015 for a review). The most dominant model of avoidance learning is Mowrer’s two-factor theory (Mowrer, 1960), which states that both Pavlovian and
instrumental learning are required for the acquisition of avoidance. This is studied by using an avoidance learning procedure during which the two types of learning are assumed to occur. During such a procedure an initially neutral cue (Conditioned Stimulus or CS) is paired with an aversive stimulus (Unconditioned Stimulus or US), a procedure that typically leads to conditioned fear responses (CRs) (e.g., subjective apprehension) towards the CS even when the US is no longer presented (First factor; Pavlovian conditioning). According to Mowrer’s two-factor theory if the CS can be avoided (e.g., shuttling for mice or a button press for humans)., and avoidance responses are successful in terminating the presentation of the CS and cancelling the US, the avoidance behaviour will be negatively reinforced by the reduction of fear due to the discontinuation of the CS (Second factor; Instrumental learning). Despite the wide influence of Mowrer’s theory in both the experimental literature and clinical practice (Krypotos et al., 2015), contemporary theories of avoidance learning have criticized Mowrer’s two-factor theory due to its inability to explain avoidance in absence of fear and in natural settings where there isn’t always a cue to precede an aversive event (Declercq, De Houwer & Baeyens,2008, Lovibond, Mitchell, Minard, Brady & Menzies, 2009). Despite this criticism, contemporary avoidance learning theories still embrace the idea that two factors play a role in the acquisition of avoidance.
The extent to which Pavlovian and Instrumental learning are both necessary for the acquisition of avoidance has also been called into question. A recent study has shown that avoidance tendencies, towards conditioned fear stimuli can be acquired with Pavlovian learning alone (Krypotos, Effting, Arnaudova, Kindt & Beckers, 2 bfdcs014). Participants first underwent a differential fear conditioning procedure wherein one initially neutral cue (e.g., picture of a cube; CS+) always preceded the presentation of an aversive stimulus (i.e., a shock, US) and another initially neutral cue (e.g., picture of a cylinder; CS-) never preceded the US. Next participants completed a symbolic approach-avoidance task (AAT) during which they had to move an onscreen manikin figure towards (approach) or away from (avoid) each CS. As electrodes were detached, avoiding the CS onscreen could not have any effect on the US, making instrumental learning almost impossible. Participants were faster to approach the CS- and avoid the CS+ than vice versa. Taken together these results suggest that
avoidance tendencies can be acquired by mere Pavlovian associations without instrumental learning.
One limitation of Krypotos et al. (2014) is that avoidance tendencies were measured only after fear conditioning, leaving room for speculation as to how the pattern of results arose. For example it is possible that participants developed approach tendencies towards the safety cue instead of avoidance tendencies towards the aversive cue. To better understand the acquisition of approach-avoidance (action) tendencies, so that possibly better treatments can be developed to treat avoidance, we need a way to measure these tendencies during the fear conditioning procedure.
A possible way to study this is by measuring changes in body posture during fear conditioning. In previous studies body posture has often been measured using the center of pressure (COP). The COP is a weight distribution measure. Shifts on the anteroposterior (AP) axis are interpreted as action tendencies. A forward shift signifies an approach tendency and a backwards shift an avoidance tendency. One study which used the COP as measurement for approach and avoidance tendencies is that by Lelard et al. (2014). In this study participants were presented with negative affective and neutral pictures. Participants were asked to stand still on a platform that measured their COP while watching the images. As predicted
participants moved significantly greater backwards in response to the negative pictures compared to the neutral pictures, suggesting an avoidance tendency towards aversive stimuli.
Eerland, Guadalupe, Franken and Zwaan (2012) used the COP to measure approach-avoidance tendencies while viewing emotional images. Participants were presented with, either pleasant, unpleasant, or neutral pictures. Each trial began with a passive viewing phase during which an image was presented, followed by a lateral movement phase during which an arrow was presented over the image, either pointing to the left or right. Participants were instructed to lean towards the direction that each arrow was pointing at. As predicted participants leaned more to the front while viewing pleasant pictures compared to neutral pictures, indicating a tendency to approach positive stimuli, but only during the passive viewing phase. Participants leaned more to the back during the lateral movement phase while viewing unpleasant pictures compared to viewing neutral pictures, indicating a tendency to avoid unpleasant stimuli. This difference did not exist during the passive viewing phase, which indicates a delay in the acquisition of avoidance tendencies. The delay in avoidance tendencies could be explained by needing more time to comprehend aversive stimuli (Eerland et al., 2012). The above mentioned studies, found approach-avoidance tendencies using the COP as measurement tool.
Although the COP has been successfully used in previous studies as a measurement of approach-avoidance tendencies, not all studies have found avoidance tendencies. Lelard et al. (2013) presented subjects with pictures of painful and non-painful situations. Participants were instructed to imagine being in the portrayed situations. The researchers expected participants to lean more towards the back while viewing the images of the painful situations compared to the non-painful situations, indicating a tendency towards avoidance. Results however showed a decrease in body sway while watching the painful situations, possibly indicating a tendency towards freezing (defined as a fear response which supresses all movement except that required for respiration; most commonly seen in animals feigning death in a life threatening situation). Gea et al. (2014) found similar results when they presented participants with video clips depicting painful, happy and neutral facial expressions. As predicted participants leaned significantly more forward while watching happy faces compared to neutral faces, possibly indicating a tendency to approach positive stimuli. While viewing the painful video clips participants did not lean back as expected, but moved less, which could indicate a tendency towards freezing.
Taken together the above mentioned studies have successfully found approach, avoidance and freezing tendencies, supporting the notion that the COP can be used as a measure in studying action tendencies while viewing emotional stimuli. However since the stimuli in previous studies already had hedonic value, they cannot shed light on the
development of action tendencies towards initially neutral cues. Participants might already have approach or avoidance tendencies towards stimuli with hedonic value before the start of the experiment. To study how avoidance develops, initially neutral cues need to be used Knowledge on the development of avoidance tendencies is important as it can help us understand how participants with anxiety disorders or phobias acquired excessive avoidance tendencies towards phobic cues.
In the present study body posture was used to measure approach-avoidance tendencies towards conditioned fear cues during acquisition. The COP was measured using the Nintendo Wii Balance Board (WBB). The WBB measures shifts in COP on two axis. The medio lateral (x) axis from left to right and the AP (y) axis from front to back (Dijkstra, Eerland, Zijlmans and Post, 2014). Measurement of the COP using the WBB has been done in a number of studies and has demonstrated good psychometric properties (Clark, Bryant, Pua, McCrory, Bennell and Hunt, 2010). Our participants first underwent a fear conditioning procedure using an initially neutral cue (e.g., either a cube or cylinder; CS+) which was paired with an aversive stimuli (e.g., a loud noise; US) while standing on the WBB. Another initially neutral cue (CS-) was never followed by the noise. Each trial was divided into a passive viewing phase and a lateral movement phase as in the Eerland et al. (2012) study, allowing postural changes to be measured over time with as few random movements as possible. The passive viewing phase consisted of the presentation of the CSs, during which participants were instructed to give vocally their expectations of the US. The lateral movement phase consisted of the presentation of an arrow over the image, pointing either to the left or the right.
Participants were instructed to lean in the direction each arrow was pointing at. The fear conditioning procedure was followed by a symbolic approach –avoidance task (AAT) as in the study by Krypotos et al., (2014).
We postulated three hypotheses. First we hypothesized finding postural reactions indicating an approach tendency towards the CS- (participants leaning forward towards the CS-) during the passive viewing phase and an avoidance tendency towards the CS+
(participants leaning away from the CS+) during the lateral movement phase (as seen in the study by Eerland et al., 2012). Secondly we hypothesized finding faster reaction times during congruent trials (avoid CS+ and approach CS-) compared to incongruent trials (avoid CS- and approach CS+) as seen in the Krypotos et al (2014) study. Lastly we predicted a positive correlation between the changes in COP and performance on the AAT.
Method Participants
Seventy one students participated in this study (51 female; mean age 23, SD 5.4). The study has been approved by the ethical committee of the UvA (CE 2014-CP-3913). All participants signed an informed consent and were given course credits or € 5,- as
compensation for their participation. Eleven participants did not give expectancy ratings in the right direction on the last two trials (see procedure) and were excluded from analysis due
to not being contingency aware of the CS-US contingencies (see Lovibond and Shanks, 2002 for a relevant discussion). Analysis are based on the remaining 60 participants (43 female; mean age 23, Standard Deviation 5.6)
Stimuli and apparatus Pictures of a cube or cylinder (50mm × 50mm) depicted from four different viewpoints against a white frame (100mm × 100mm) served as the CS+ and CS-. The assignment of the pictures to the CS+ or the CS- was counterbalanced across participants. These pictures were used during the fear conditioning procedure and the Stimulus Response Compatibility Task (SRCT). During the SRCT the frame changed to either a landscape frame 100mm × 55mm or a portrait frame 55mm × 100mm.
The US was a burst of white noise presented for 1 second with an intensity of just under 104dB.
During fear conditioning the Wii Balance Boards (WBB) was used to assess body posture, measuring changes of COP on two axis. Approach and avoidance tendencies were measured on the y-axis, with a positive shift indicating avoidance tendencies and a negative shift indicating approach tendencies.
Two questionnaires were used to measure state and trait anxiety. The ‘State-Trait Anxiety Inventory’ (STAI) is comprised of two subscales, each of 20 items, one measuring state anxiety and the other trait anxiety. The STAI-S was administered at the beginning of the experiment. This subscale has a test-retest reliability of 0.33 and an internal consistency of 0.86-0.93. The STAI-T has a test-retest reliability of 0.73-0.86 and an internal consistency of 0.90 (Spielberger & Gorsuch, 1983; Dutch version by van der Ploeg, 2000).The ‘Anxiety Sensitivity Index’ (ASI) was administered after the AAT to measure the tendency to fear anxiety-related bodily sensations. The ASI consists of 16 items divided over four factors: trembling and fainting, cardio and gastro, cognitive and public. Internal consistency of the four factors respectively (Dutch version) is 0.74, 0.43, 0.68 and 0.75. Overall internal consistency is 0.83 (Boelen and Reijntjes, 2009).
Procedure
After reading the information brochure participants signed the informed consent. They were asked to fill in the state section of the STAI (STAI-S), this was to check for any extreme values in state anxiety. After filling in the questionnaire, participants removed their shoes, had their height measured and stepped on the WBB. Before the conditioning procedure began, the WBB recorded their neutral stance (calibration phase). During fear conditioning two objects were presented on a computer screen (see Figure 1 for a graphic explanation of a conditioning trial). Instructions stated that one object would always be followed by a loud noise and the other object would never be followed by a loud noise. Participants were asked to learn to predict after which object the loud noise would occur while standing on the WBB. The main task consisted of 16 trials equally divided into two blocks with a short break in between. Each CS was presented eight times (twice per viewpoint). Participants verbally reported their US expectations on a scale from -5 (certainly no loud noise) to 5 (certainly a loud noise), which were noted down by the experimenter, who was standing behind the participant. After 3000msec a black arrow appeared on screen instructing participants to lean left or right. During the CS+ trials, the US occurred after the arrow, 5500msec after trial initiation. Inter-trial intervals (ITIs) lasted for 2 seconds, participants were asked to return to their initial position on the centre of the board using the crosshair on the screen for the next
trial to start. The order of the CS presentation was semi-random, with the restriction that no more than two CSs of the same kind (CS+ or CS-) would follow one another.
After completing the fear conditioning procedure, participants were asked to put their shoes back on and sit behind another computer screen for the SRCT. The SRCT consisted of 8 practice trials and 32 test trials divided into two blocks. See Figure 2 for a graphic
explanation of a trial. At the beginning of each trial a white puppet (manikin) would appear either on the top half or bottom half of the screen. After 1500msec a picture of a CS (CS+ or CS-) would appear on the other half of the screen. Participants were instructed to either move the manikin towards the CS or away from the CS using the keyboard. Movement towards or away from the CSs depended on the orientation of the white frame surrounding the CS
(landscape or portrait). Instructions were counterbalanced per block across participants. Upon pressing the ‘Y’ key labelled with an upward arrow or the ‘B’ key labelled with a downward arrow the manikin would begin to move and disappear after 5000msec. In case of error responses, a red cross would appear on screen. The ITIs were fixed to 2000msec.
Following the SRCT, pictures of the CSs from each viewpoint were presented. Participants were asked to use the mouse to rate each picture on pleasantness using a nine-point scale visible on the bottom of the screen.
After completing the computer task participants were asked to fill in the ASI and the trait section of the STAI (STAI-T), so that we were able to check for extreme values in trait anxiety. This was followed by an exit questionnaire in which they were asked to fill in their demographic details and rate the US on pleasantness, intensity and degree of startlingness. After this an interview followed during which they were asked about the contingencies between the CSs and the US.
Statistical Analysis
US-expectancy ratings were analysed with a 2 (Stimulus: CS+ vs. CS-) × 8 (Trial: 1 to 8) repeated measures ANOVA, with stimulus and trial as within-subject factors. For each participant, the COP was calculated (each stimulus CS- / CS+, by trial 1 to 8, by axis x / y combination) every 500 msec. We divided the COP data into two sections for analysis, the passive viewing phase (0msec-3000msec after trial initiation) and the lateral movement phase (3000msec-5500msec after trial initiation). Mean scores were calculated for each period separately on the x axis and the y axis. Body posture mean scores were analysed using two separate, 2 (Stimulus: CS+ vs. CS-) × 8 (Trial: 1 to 8) repeated measures ANOVAs, using Greenhouse-Geisser correction as necessary, with stimulus and trial as within-subject factors.
For the SRCT, practice trials, test trials with incorrect responses (0.39%) and test trials longer than 3000msec (0.01%) were omitted from analyses. For each participant, median reaction times (RTs) were calculated (each stimulus, CS- / CS+, by response type, approach / avoid, combination). RTs were analysed using a 2 (Stimulus: CS+ vs. CS-) × 2 (Response: Approach vs. Avoid) repeated measures ANOVA, with stimulus and response styles as within subject factors.
Results
Pavlovian fear conditioning procedure. Participants learned to expect the US after being presented with the CS+ and learned not to expect the US after the CS-,
F(1,59)=813.82,p<.001; ηp2 = .93. Figure 3 shows the US expectancy ratings visually. The stimulus had no significant effects on body posture F(1,59)=.03, p = .869; ηp2 =.00 (Passive: F(1,59)=2.14, p = .149; ηp2 = .04. Movement: F(1,59)=1.14, p = .289; ηp2 =.02). Figure 4 shows the results of both phases together and figures 5 and 6 portray the results of each phase, the passive viewing and lateral movement. The trials however did effect body posture significantly, F(7,413)=4.94, p<.01; ηp2 = .08 (Passive: F(7,413)=3.87, p<.01; ηp2 = .06. Movement: F(7,413)=3.85, p<.05; ηp2 = .06.). Participants leaned significantly more to the front and to the back on later trails than during the first trials, most probably due to learning effects.
SRCT. There were no significant differences between congruent and incongruent trials on the SRCT, F(1,59)=2.74, p = .103;ηp2 =.01 (See figure 7). These results indicate that fear conditioning did not seem to result in the acquisition of avoidance tendencies.
Discussion
Our goal was to study how avoidance tendencies towards conditioned cues are acquired. To investigate this we used body posture as a measure of approach-avoidance tendencies during a fear conditioning procedure. Participants learned to expect the US after the CS+ and not after the CS-. Body posture changed significantly as the trials progressed, indicating that the participants understood what was asked of them and were able to accomplish the movements as instructed.
Body posture is a rather new way of measuring approach-avoidance tendencies and has not been used in many research programs. Studies that did use body posture as a measurement for approach-avoidance tendencies, used stimuli which already had hedonic value (i.g. pleasant pictures of animals, neutral pictures of household appliances, unpleasant pictures of scared people as in Eerland et al., 2012). The present study was the first to use body posture to measure approach-avoidance tendencies towards conditioned cues. These are cues which are initially neutral, allowing the current experiment to study approach-avoidance tendencies while they are acquired as opposed to measuring already existing
approach-avoidance tendencies which is the case with stimuli with hedonic value.
Even though the current study is the first in its kind, the methodology was based on earlier research. The instructions for the fear conditioning procedure were as in the study by Eerland et al. (2012) and the fear conditioning itself and SRCT were as in the study by Krypotos et al. (2014). The latter study found evidence for the acquisition of avoidance tendencies following mere Pavlovian fear conditioning.
The current study did not find any approach-avoidance tendencies towards the conditioned cues. It was predicted that participants would lean more to the back while viewing the CS+ and more to the front while viewing the CS-, this difference was not found. The data was divided into two timeframes per trial. A passive viewing phase and a lateral movement phase. There were no differences found in body posture during the individual phases or both phases together.
As this was the first time that body posture was used during fear acquisition, it is possible that body posture is not a good measure for approach-avoidance tendencies towards initially neutral cues. This could explain why no approach-avoidance tendencies were found during the fear conditioning procedure.
An SRCT was administered after fear conditioning. It was predicted that participants would be faster to approach the CS- and avoid the CS+ compared to avoiding the CS- and approaching the CS+ (congruent vs. incongruent trials). This difference was not found. There were no difference in reaction times between the congruent and incongruent trials. As the SRCT is a measure of approach-avoidance tendencies towards conditioned cues and has been used in this capacity in earlier research, these results could indicate that no
approach-avoidance tendencies were acquired during the fear conditioning procedure.
A possible explanation for why no approach-avoidance tendencies were acquired during fear conditioning is the US which was used. In the study by Krypotos et al. (2014) the US was an electric shock. The current study, which used the same stimuli as in the Krypotos et al. study, used a loud noise as the US instead of an electric shock. It is probable that the loud noise was not strong enough for participants to acquire approach-avoidance tendencies towards the conditioned stimuli. Participants rated the US on pleasantness, intensity and startlingness (See figure 8 for results of the current study). US ratings did not differ from the ones given in the earlier study. Even though the ratings did not show a difference, it is
possible that a shock is experienced in a different way than a loud noise and perhaps harder to get used to.
The current experiment tried to study how avoidance tendencies towards conditioned cues are acquired during fear conditioning. Results indicate that avoidance tendencies were most probably not acquired during fear conditioning. This leaves the question as to how avoidance tendencies towards conditioning cues are acquired still unanswered. It is a relevant question, because knowing how avoidance tendencies are acquired could contribute to further studies finding better ways of treating overt avoidance, which is a major part of many
psychological disorders.
Future studies could try replicating the current experiment using a more aversive US. It is possible that using an electric shock as US (as in the study by Krypotos et al., 2014) leads to different results. Using a totally different US might also work, for example, the CS+ could be paired with an aversive picture (i. g. scenes of war) and the CS- either with none or a picture with positive value (i. g. scenes of flowers).
Another suggestion for future research is to replicate this study and add a second condition to it. One condition consisting of fear conditioning with mere Pavlovian learning and another consisting of fear conditioning with both Pavlovian and instrumental learning. Participants undergoing a Pavlovian fear conditioning procedure could then be compared to participants who are able to overtly avoid the US (i. g. by pressing a button). This might lead to new knowledge about how avoidance tendencies are acquired and how they are related to overt avoidance which in turn could lead to new treatments of avoidance.
Even though the current study was not able to investigate how avoidance tendencies towards conditioned cues are acquired and how they develop during fear conditioning, it can be viewed as a first step in an exciting new way of researching approach-avoidance
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Figures
Figure 1 Visualization of a trial during fear conditioning. A cube or cylinder is presented on
screen. After 3000msec. an arrow appears over the CS showing participants which side to lean and then disappears. During the CS+ trials, 5500msec after trial initiation the US is presented through headphones.
Figure 2 Visualization of a trial during the SRCT. At the beginning of the trial the manikin
appears on either the bottom half or the top half of the screen. The CS appears 1500msec. after trial initiation on the other half of the screen. According to the frame surrounding the CS, the participants were instructed to either move the manikin towards the CS or away from it. In case of an incorrect response, a red cross appeared. Inter-Trial Interval (ITI) was set at 2000msec. after trial initiation.
Figure 3 US expectations for the CS+ and the CS- per trial during the fear conditioning
Figure 4 Body posture towards the CS+ and towards the CS- per trial during fear
Figure 5 Body posture towards the CS+ and the CS- per trial during the passive viewing
Figure 6 Body posture towards the CS+ and the CS- per trial during the lateral movement
