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Affective modulation of conditioned eyeblinks
Biological Psychology 82 (2009) 192–194
Contents lists available at ScienceDirect
Biological Psychology journal homepage: www.elsevier.com/locate/biopsycho
Brief report
Affective modulation of conditioned eyeblinks Suvi Karla a, Timo Ruusuvirta b,c,d, Jan Wikgren a,* a
Department of Psychology, University of Jyva¨skyla¨, P.O. Box 35, FIN-40014 Jyva¨skyla¨, Finland Turku Institute for Advanced Studies, Centre for Cognitive Neuroscience, Department of Psychology, University of Turku/Turku School of Economics, Assistentinkatu 7, FIN-20014 Turku, Finland c Department of Psychology, University of Tampere, Kalevantie 5, FIN-33014 Tampere, Finland d Cognitive Brain Research Unit, Department of Psychology, University of Jyva¨skyla¨, FIN-00014, Helsinki, Finland b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 3 February 2009 Accepted 28 June 2009 Available online 4 July 2009
Affective states are known to modulate reflexive actions. Aversive states potentiate defensive reflexes while appetitive states diminish them. The present study examined whether the same holds for associatively learned defensive eyeblinks to mild, initially neutral auditory stimuli. First, delay eyeblink conditioning was applied to human participants while they viewed emotionally neutral images. Next, the conditioned eyeblink responses (CRs) of the participants were tested during the viewing of unpleasant, neutral, or pleasant images. The most vigorous CRs were found during the unpleasant images, although they did not differ between neutral and pleasant images. The results add to the motivational priming hypothesis by demonstrating its partial applicability to associatively learned defensive behaviour. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Reflex Eyeblink conditioning Emotion IAPS
1. Introduction The motivational priming hypothesis (for details see, e.g. Lang et al., 1990) states that reflexive actions are augmented when they are congruent with the ongoing motivational state. In practice, the hypothesis states that negative emotions activate the brain’s aversive motivational system and prime defensive reflexes. Experimentally, motivational states (and emotions) are typically induced by presenting images varying in content from unpleasant to pleasant. Indeed, the motivational priming hypothesis has withstood a plethora of tests combining picture viewing with an acoustic startle probe. Additionally, other types of emotional background stimuli have been utilized; for example, movies (Jansen and Frijda, 1994; Kaviani et al., 1999), words (Aitken et al., 1999), odours (Miltner et al., 1994; Ehrlichman et al., 1995 Ehrlichman et al., 1997; Prehn et al., 2006), imagery (Vrana and Lang, 1990) or stimuli previously paired with negative consequences (Grillon, 2002; A˚sli and Flaten, 2007; Mallan and Lipp, 2007). Likewise, tactile eyeblink reflexes, evoked by mild airpuffs (Hawk and Cook, 1997) have been shown to be modulated by emotional background stimuli. Only reflexes of a neutral, nondefensive nature, such as the tendon reflex, seem to be unaffected by such modulation (Bonnet et al., 1995).
* Corresponding author. Tel.: +359 14 260 2848; fax: +358 14 260 2841. E-mail address: jan.wikgren@jyu.fi (J. Wikgren). 0301-0511/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.biopsycho.2009.06.008
The motivational priming hypothesis (Lang et al., 1990) implies that any defensively motivated behaviour, not only innate reflexes, should be modulated by emotional state. However, it is unclear whether a probe for emotional priming could be based on associative plasticity. The present study aimed at investigating whether conditioned eyeblinks in response to initially neutral non-arousing tones (e.g. Thompson et al., 1998) could provide such a probe. The adult human participants were first subjected to classical eyeblink conditioning while they viewed emotionally neutral images. Their CRs were then assessed during the viewing of pleasant, neutral, and unpleasant images. 2. Methods 2.1. Subjects Twenty-five university students (age range 20–28 years; mean age 21 years male, 24 years females) participated in the experiment. As compensation for their participation, the students received a ticket to the local cinema. The research ethics committee of the University of Jyva¨skyla¨ approved the study. 2.2. Stimuli and apparatus The tone CS (70 dB, 500 ms, 1000 Hz) was presented via a loudspeaker above the participant’s head. The US was an airpuff (0.5 bar source pressure, 100 ms) to the outer corner of the right eye, delivered via a plastic tube attached to specially designed goggles. The emotional stimuli were 50 pictures, 40 neutral (e.g. household objects and neutral faces), 10 pleasant (e.g. food and animals), and 10 unpleasant (e.g. violence and spiders) randomly selected for each participant from a subset of the
S. Karla et al. / Biological Psychology 82 (2009) 192–194
193
International Affective Picture System1 (IAPS; The Center for Research in Psychophysiology, 2001). The mean normative valence ratings for the pictures used were 7.53, 5.00 and 2.67, respectively (1–9 scale, low values representing unpleasantness) and arousal ratings were 4.85, 2.97, and 5.91 (1–9 scale) for the pleasant, neutral, and unpleasant categories, respectively. 2.3. Procedure The participants were informed that their task was to sit in a comfortable chair in a dimly lit room and to watch images presented on a 17 in. computer monitor approximately 1 m in front of them, while occasional tones and airpuffs to the corner of the eye were administered. Eyeblinks were recorded as EMG activity of the orbicularis oculi muscle beneath the right eye. The ground electrode was attached to the forehead. The raw EMG signal was fed into custom-built amplifier, digitized (sampling rate 1000 Hz), rectified, and digitally off-line filtered with low-pass (<20 Hz) filter. The experiment consisted of two phases. In the acquisition phase, 80 CS–US pairs were presented during viewing of pictures, presented in a random order and selected from among 40 neutral Images.1 In the test phase, 30 CS–US pairs were presented during presentation of pictures varying in emotional content (10 pleasant, 10 neutral, and 10 unpleasant pictures in presented pseudorandom order). During both phases, the pictures were visible for 6 s and CS–US pairs were presented within that time-frame so that the onset of the CS varied randomly between 1 and 5 s from the image onset. The CS and US were presented in a delayed fashion with an inter-stimulus interval (onset-to-onset) of 400 ms. The inter-trial intervals varied between 15 and 24 s, during which the monitor was black. E-Prime software was used to control the experiment. 2.4. Data analysis To minimize the between-subject variability in the EMG magnitude, the signal was standardized for each participant by expressing each data point as a percentage of the average response magnitude across the first five unconditioned responses. All off-line signal processing was carried out using Matlab with the Signal Processing Toolbox. Three periods were determined for the purpose of the analyses: baseline (200 ms before the onset of the CS), CR (200 ms before the onset of the US) and UR (200 ms after the onset of the US). For each trial, the maximum CR and UR magnitudes were determined from corresponding 200 ms periods using the standardized EMG signals and then averaged for eight conditioning blocks (10 trials each) in the acquisition phase, and for each image content in the test phase. Variation in spontaneous EMG activity was determined from the baseline activity. An eyeblink was considered to have occurred when the maximum EMG activity in a given period exceeded the spontaneous activity by more than 5 standard deviations. Blink probability was thus determined in each trial for baseline and CR periods. The CR probability was then calculated by subtracting the blink probability in the baseline period from that of the CR period in each trial block. Analysis of variance for repeated measures and subsequent paired samples t-tests with Bonferroni-correction were used to analyse the effects of conditioning and image content. Greenhouse–Geisser corrected degrees of freedom were used if the sphericity assumption was violated.
3. Results 3.1. Development of the CR As a function of training, average CR magnitude increased from 12.59 (SEM = 1.54) to 19.02 (2.34) standardized units and CR probability from 40.0 (7.64) to 74.0 (4.43)%. There was a significant main effect of conditioning for both CR magnitude [F(7,168) = 6.52, p < 0.001, h2partial = 0.214] and probability [F(7,168) = 10.96, p < 0.05, h2partial = 0.313]. Subsequent paired comparisons verified that both CR magnitude and CR probability in blocks 2–8 were significantly higher than in the first block [CR magnitude: 1
IAPS-slide numbers: Neutral: 2190, 2200, 2210, 2393, 2514, 2600, 5130, 5500, 5510, 5740, 5750, 5900, 7000, 7002, 7004, 7009, 7010, 7020, 7030, 7031, 7050, 7060, 7080, 7090, 7100, 7110, 7130, 7150, 7160, 7170, 7180, 7182, 7184, 7211, 7217, 7233, 7500, 7550, 7700, 7705. Pleasant: 1440, 1460, 1600, 1603, 1610, 1620, 1750, 1920, 2040, 2050, 2071, 2080, 2091, 2208, 2250, 2299, 2331, 4650, 4660, 4680, 5200, 7200, 7230, 7270, 7280, 7330, 7350, 8030, 8080, 8120, 8200, 8510. Unpleasant: 1070, 1090, 1110, 1114, 1120, 1205, 1274, 1280, 1300, 2053, 2095, 2120, 2141, 2205, 2276, 2683, 2710, 2800, 3000, 3010, 3030, 3100, 3120, 3130, 3140, 3150, 3530, 6020, 6190, 6200, 6230, 6370, 6415, 6555, 7380, 9001, 9040, 9041, 9050, 9340, 9342, 9490.
Fig. 1. CR magnitudes were modulated as a function of image content. Unpleasant (UN) images evoked the largest and neutral pictures (NE) the smallest CRs. Paired comparisons (t-tests) on standardized CR magnitude showed significant differences between pleasant (PL) and unpleasant (UN) and also between neutral (NE) and unpleasant (UN) images. UR magnitudes did not differ significantly between image contents.
t(24) = 3.39–4.47, p < 0.01; CR probability: t(24) = 2.92–4.47, p < 0.01]. Comparison of CR magnitude and probability in blocks 3–8 with that in block 2 only yielded a statistically significant difference for CR probability [block 2 vs. block 8: t(24) = 2.17, p < 0.05], suggesting that the level of conditioned responding was relatively stable from the block 2 onwards. 3.2. Effect of image content on CR and UR magnitudes Fig. 1 shows the CR and UR magnitudes as a function of picture content in the test phase. The picture content had a significant main effect on CR magnitude [F(2,48) = 6.76, p < 0.01, h2partial = 0.220], but not on CR probability [F(2,48) = 0.63, p = 0.54, h2partial = 0.026] or UR magnitude [F(2,48) = 1.80, p = 0.178, h2partial = 0.069]. Subsequent paired comparisons showed higher CR magnitudes during unpleasant relative to pleasant [t(24) = 2.68, p < 0.05] and relative to neutral pictures [t(24) = 2.82, p < 0.01]. No difference was observed between neutral and pleasant pictures [t(24) = 0.15, p = 0.879]. 4. Discussion We investigated the applicability of the motivational priming hypothesis (Lang et al., 1990) to associatively learned, defensive eyeblinks. We found that defensive eyeblink CRs were augmented during unpleasant pictures. This augmentation is analogous to that of startle responses in similar contexts (Lang et al., 1990). Our finding, therefore, suggests that emotional state also affects associatively learned, motivationally driven, yet emotionally relatively neutral, behavioural acts. This adds to the general validity of the motivational priming hypothesis (Lang et al., 1990). However, the lack of observable CR diminution for pleasant relative to neutral pictures was in contrast to the previous findings of such diminution in startle eyeblinks (Lang et al., 1990). The cause of this discrepancy remains unclear. Nevertheless, we must acknowledge that CRs and URs recruit partially distinct neural networks and mechanisms. In other words, whereas eyeblink reflexes are driven by simple brain-stem pathways, conditioned
194
S. Karla et al. / Biological Psychology 82 (2009) 192–194
eyeblinks also depend on a distinct cerebellar learning circuit (e.g. Steinmetz, 2000), which might be differently affected by experienced valence, specifically concerning pleasant states. Unexpectedly, however, the emotional state did not modulate the magnitude of airpuff URs. The reason for this was most likely methodological. The high US intensity used to assure robust learning was very likely the cause of a ceiling effect for UR magnitude, even with pleasant pictures. In line with this, emotional state has been shown to modulate airpuff-induced eyeblinks in the case of milder airpuffs (Hawk and Cook, 1997). To conclude, our findings add to the motivational priming hypothesis (Lang et al., 1990) by showing that unpleasant affective states also augment associatively learned defensive responses. Future studies should address the lack of their diminution by pleasant affective states. Acknowledgements The study was funded by a grant from the Academy of Finland to JW (114258). The authors wish to thank Lauri Viljanto for technical help, Dave Lavond for commenting an earlier version of the manuscript and Michael Dutton for revising our English. References Aitken, C.J., Siddle, D.A., Lipp, O.V., 1999. The effects of threat and nonthreat word lead stimuli on blink modification. Psychophysiology 36, 699–705. A˚sli, O., Flaten, M.A., 2007. Conditioned facilitation of the unconditioned reflex after classical eyeblink conditioning. International Journal of Psychophysiology 67, 17–22.
Bonnet, M., Bradley, M.M., Lang, P.J., Requin, J., 1995. Modulation of spinal reflexes: arousal, pleasure, action. Psychophysiology 32, 367–372. Ehrlichman, H., Brown, S., Zhu, J., Warrenburg, S., 1995. Startle reflex modulation during exposure to pleasant and unpleasant odors. Psychophysiology 32, 150–154. Ehrlichman, H., Kuhl, S.B., Zhu, J., Warrenburg, S., 1997. Startle reflex modulation by pleasant and unpleasant odors in a between-subjects design. Psychophysiology 34, 726–729. Grillon, C., 2002. Associative learning deficits increase symptoms of anxiety in humans. Biological Psychiatry 51, 851–858. Hawk, L.W., Cook 3rd, E.W., 1997. Affective modulation of tactile startle. Psychophysiology 34, 23–31. Jansen, D.M., Frijda, N.H., 1994. Modulation of the acoustic startle response by filminduced fear and sexual arousal. Psychophysiology 31, 565–571. Kaviani, H., Gray, J.A., Checkley, S.A., Kumari, V., Wilson, G.D., 1999. Modulation of the acoustic startle reflex by emotionally-toned film-clips. International Journal of Psychophysiology 32, 47–54. Lang, P.J., Bradley, M.M., Cuthbert, B.N., 1990. Emotion, attention and startle reflex. Psychological Review 97, 377–395. Lang, P.J., Bradley, M.M., Cuthbert, B.N., 2001. International affective picture system (IAPS). Instruction manual and affective ratings. Technical report A-5, The Center for research in psychophysiology, University of Florida. Mallan, K.M., Lipp, O.V., 2007. Does emotion modulate the blink reflex in human conditioning? Startle potentiation during pleasant and unpleasant cues in the picture-picture paradigm. Psychophysiology 44, 737–748. Miltner, W., Matjak, M., Braun, C., Diekmann, H., Brody, S., 1994. Emotional qualities of odors and their influence on the startle reflex in humans. Psychophysiology 31, 107–110. Prehn, A., Ohrt, A., Sojka, B., Ferstl, R., Pause, B.M., 2006. Chemosensory anxiety signals augment the startle reflex in humans. Neuroscience Letters 394, 127–130. Steinmetz, J.E., 2000. Brain substrates of classical conditioning: a highly localized but also distributed system. Behavioral Brain Research 110, 13–24. Thompson, R.F., Thompson, J.K., Kim, J.J., Krupa, D.J., Shinkman, P.G., 1998. The nature of reinforcement in cerebellar learning. Neurobiology of Learning and Memory 70, 150–176. Vrana, S.R., Lang, P.J., 1990. Fear imagery and startle-probe reflex. Journal of Abnormal Psychology 99, 189–197.
Contents lists available at ScienceDirect
Biological Psychology journal homepage: www.elsevier.com/locate/biopsycho
Brief report
Affective modulation of conditioned eyeblinks Suvi Karla a, Timo Ruusuvirta b,c,d, Jan Wikgren a,* a
Department of Psychology, University of Jyva¨skyla¨, P.O. Box 35, FIN-40014 Jyva¨skyla¨, Finland Turku Institute for Advanced Studies, Centre for Cognitive Neuroscience, Department of Psychology, University of Turku/Turku School of Economics, Assistentinkatu 7, FIN-20014 Turku, Finland c Department of Psychology, University of Tampere, Kalevantie 5, FIN-33014 Tampere, Finland d Cognitive Brain Research Unit, Department of Psychology, University of Jyva¨skyla¨, FIN-00014, Helsinki, Finland b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 3 February 2009 Accepted 28 June 2009 Available online 4 July 2009
Affective states are known to modulate reflexive actions. Aversive states potentiate defensive reflexes while appetitive states diminish them. The present study examined whether the same holds for associatively learned defensive eyeblinks to mild, initially neutral auditory stimuli. First, delay eyeblink conditioning was applied to human participants while they viewed emotionally neutral images. Next, the conditioned eyeblink responses (CRs) of the participants were tested during the viewing of unpleasant, neutral, or pleasant images. The most vigorous CRs were found during the unpleasant images, although they did not differ between neutral and pleasant images. The results add to the motivational priming hypothesis by demonstrating its partial applicability to associatively learned defensive behaviour. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Reflex Eyeblink conditioning Emotion IAPS
1. Introduction The motivational priming hypothesis (for details see, e.g. Lang et al., 1990) states that reflexive actions are augmented when they are congruent with the ongoing motivational state. In practice, the hypothesis states that negative emotions activate the brain’s aversive motivational system and prime defensive reflexes. Experimentally, motivational states (and emotions) are typically induced by presenting images varying in content from unpleasant to pleasant. Indeed, the motivational priming hypothesis has withstood a plethora of tests combining picture viewing with an acoustic startle probe. Additionally, other types of emotional background stimuli have been utilized; for example, movies (Jansen and Frijda, 1994; Kaviani et al., 1999), words (Aitken et al., 1999), odours (Miltner et al., 1994; Ehrlichman et al., 1995 Ehrlichman et al., 1997; Prehn et al., 2006), imagery (Vrana and Lang, 1990) or stimuli previously paired with negative consequences (Grillon, 2002; A˚sli and Flaten, 2007; Mallan and Lipp, 2007). Likewise, tactile eyeblink reflexes, evoked by mild airpuffs (Hawk and Cook, 1997) have been shown to be modulated by emotional background stimuli. Only reflexes of a neutral, nondefensive nature, such as the tendon reflex, seem to be unaffected by such modulation (Bonnet et al., 1995).
* Corresponding author. Tel.: +359 14 260 2848; fax: +358 14 260 2841. E-mail address: jan.wikgren@jyu.fi (J. Wikgren). 0301-0511/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.biopsycho.2009.06.008
The motivational priming hypothesis (Lang et al., 1990) implies that any defensively motivated behaviour, not only innate reflexes, should be modulated by emotional state. However, it is unclear whether a probe for emotional priming could be based on associative plasticity. The present study aimed at investigating whether conditioned eyeblinks in response to initially neutral non-arousing tones (e.g. Thompson et al., 1998) could provide such a probe. The adult human participants were first subjected to classical eyeblink conditioning while they viewed emotionally neutral images. Their CRs were then assessed during the viewing of pleasant, neutral, and unpleasant images. 2. Methods 2.1. Subjects Twenty-five university students (age range 20–28 years; mean age 21 years male, 24 years females) participated in the experiment. As compensation for their participation, the students received a ticket to the local cinema. The research ethics committee of the University of Jyva¨skyla¨ approved the study. 2.2. Stimuli and apparatus The tone CS (70 dB, 500 ms, 1000 Hz) was presented via a loudspeaker above the participant’s head. The US was an airpuff (0.5 bar source pressure, 100 ms) to the outer corner of the right eye, delivered via a plastic tube attached to specially designed goggles. The emotional stimuli were 50 pictures, 40 neutral (e.g. household objects and neutral faces), 10 pleasant (e.g. food and animals), and 10 unpleasant (e.g. violence and spiders) randomly selected for each participant from a subset of the
S. Karla et al. / Biological Psychology 82 (2009) 192–194
193
International Affective Picture System1 (IAPS; The Center for Research in Psychophysiology, 2001). The mean normative valence ratings for the pictures used were 7.53, 5.00 and 2.67, respectively (1–9 scale, low values representing unpleasantness) and arousal ratings were 4.85, 2.97, and 5.91 (1–9 scale) for the pleasant, neutral, and unpleasant categories, respectively. 2.3. Procedure The participants were informed that their task was to sit in a comfortable chair in a dimly lit room and to watch images presented on a 17 in. computer monitor approximately 1 m in front of them, while occasional tones and airpuffs to the corner of the eye were administered. Eyeblinks were recorded as EMG activity of the orbicularis oculi muscle beneath the right eye. The ground electrode was attached to the forehead. The raw EMG signal was fed into custom-built amplifier, digitized (sampling rate 1000 Hz), rectified, and digitally off-line filtered with low-pass (<20 Hz) filter. The experiment consisted of two phases. In the acquisition phase, 80 CS–US pairs were presented during viewing of pictures, presented in a random order and selected from among 40 neutral Images.1 In the test phase, 30 CS–US pairs were presented during presentation of pictures varying in emotional content (10 pleasant, 10 neutral, and 10 unpleasant pictures in presented pseudorandom order). During both phases, the pictures were visible for 6 s and CS–US pairs were presented within that time-frame so that the onset of the CS varied randomly between 1 and 5 s from the image onset. The CS and US were presented in a delayed fashion with an inter-stimulus interval (onset-to-onset) of 400 ms. The inter-trial intervals varied between 15 and 24 s, during which the monitor was black. E-Prime software was used to control the experiment. 2.4. Data analysis To minimize the between-subject variability in the EMG magnitude, the signal was standardized for each participant by expressing each data point as a percentage of the average response magnitude across the first five unconditioned responses. All off-line signal processing was carried out using Matlab with the Signal Processing Toolbox. Three periods were determined for the purpose of the analyses: baseline (200 ms before the onset of the CS), CR (200 ms before the onset of the US) and UR (200 ms after the onset of the US). For each trial, the maximum CR and UR magnitudes were determined from corresponding 200 ms periods using the standardized EMG signals and then averaged for eight conditioning blocks (10 trials each) in the acquisition phase, and for each image content in the test phase. Variation in spontaneous EMG activity was determined from the baseline activity. An eyeblink was considered to have occurred when the maximum EMG activity in a given period exceeded the spontaneous activity by more than 5 standard deviations. Blink probability was thus determined in each trial for baseline and CR periods. The CR probability was then calculated by subtracting the blink probability in the baseline period from that of the CR period in each trial block. Analysis of variance for repeated measures and subsequent paired samples t-tests with Bonferroni-correction were used to analyse the effects of conditioning and image content. Greenhouse–Geisser corrected degrees of freedom were used if the sphericity assumption was violated.
3. Results 3.1. Development of the CR As a function of training, average CR magnitude increased from 12.59 (SEM = 1.54) to 19.02 (2.34) standardized units and CR probability from 40.0 (7.64) to 74.0 (4.43)%. There was a significant main effect of conditioning for both CR magnitude [F(7,168) = 6.52, p < 0.001, h2partial = 0.214] and probability [F(7,168) = 10.96, p < 0.05, h2partial = 0.313]. Subsequent paired comparisons verified that both CR magnitude and CR probability in blocks 2–8 were significantly higher than in the first block [CR magnitude: 1
IAPS-slide numbers: Neutral: 2190, 2200, 2210, 2393, 2514, 2600, 5130, 5500, 5510, 5740, 5750, 5900, 7000, 7002, 7004, 7009, 7010, 7020, 7030, 7031, 7050, 7060, 7080, 7090, 7100, 7110, 7130, 7150, 7160, 7170, 7180, 7182, 7184, 7211, 7217, 7233, 7500, 7550, 7700, 7705. Pleasant: 1440, 1460, 1600, 1603, 1610, 1620, 1750, 1920, 2040, 2050, 2071, 2080, 2091, 2208, 2250, 2299, 2331, 4650, 4660, 4680, 5200, 7200, 7230, 7270, 7280, 7330, 7350, 8030, 8080, 8120, 8200, 8510. Unpleasant: 1070, 1090, 1110, 1114, 1120, 1205, 1274, 1280, 1300, 2053, 2095, 2120, 2141, 2205, 2276, 2683, 2710, 2800, 3000, 3010, 3030, 3100, 3120, 3130, 3140, 3150, 3530, 6020, 6190, 6200, 6230, 6370, 6415, 6555, 7380, 9001, 9040, 9041, 9050, 9340, 9342, 9490.
Fig. 1. CR magnitudes were modulated as a function of image content. Unpleasant (UN) images evoked the largest and neutral pictures (NE) the smallest CRs. Paired comparisons (t-tests) on standardized CR magnitude showed significant differences between pleasant (PL) and unpleasant (UN) and also between neutral (NE) and unpleasant (UN) images. UR magnitudes did not differ significantly between image contents.
t(24) = 3.39–4.47, p < 0.01; CR probability: t(24) = 2.92–4.47, p < 0.01]. Comparison of CR magnitude and probability in blocks 3–8 with that in block 2 only yielded a statistically significant difference for CR probability [block 2 vs. block 8: t(24) = 2.17, p < 0.05], suggesting that the level of conditioned responding was relatively stable from the block 2 onwards. 3.2. Effect of image content on CR and UR magnitudes Fig. 1 shows the CR and UR magnitudes as a function of picture content in the test phase. The picture content had a significant main effect on CR magnitude [F(2,48) = 6.76, p < 0.01, h2partial = 0.220], but not on CR probability [F(2,48) = 0.63, p = 0.54, h2partial = 0.026] or UR magnitude [F(2,48) = 1.80, p = 0.178, h2partial = 0.069]. Subsequent paired comparisons showed higher CR magnitudes during unpleasant relative to pleasant [t(24) = 2.68, p < 0.05] and relative to neutral pictures [t(24) = 2.82, p < 0.01]. No difference was observed between neutral and pleasant pictures [t(24) = 0.15, p = 0.879]. 4. Discussion We investigated the applicability of the motivational priming hypothesis (Lang et al., 1990) to associatively learned, defensive eyeblinks. We found that defensive eyeblink CRs were augmented during unpleasant pictures. This augmentation is analogous to that of startle responses in similar contexts (Lang et al., 1990). Our finding, therefore, suggests that emotional state also affects associatively learned, motivationally driven, yet emotionally relatively neutral, behavioural acts. This adds to the general validity of the motivational priming hypothesis (Lang et al., 1990). However, the lack of observable CR diminution for pleasant relative to neutral pictures was in contrast to the previous findings of such diminution in startle eyeblinks (Lang et al., 1990). The cause of this discrepancy remains unclear. Nevertheless, we must acknowledge that CRs and URs recruit partially distinct neural networks and mechanisms. In other words, whereas eyeblink reflexes are driven by simple brain-stem pathways, conditioned
194
S. Karla et al. / Biological Psychology 82 (2009) 192–194
eyeblinks also depend on a distinct cerebellar learning circuit (e.g. Steinmetz, 2000), which might be differently affected by experienced valence, specifically concerning pleasant states. Unexpectedly, however, the emotional state did not modulate the magnitude of airpuff URs. The reason for this was most likely methodological. The high US intensity used to assure robust learning was very likely the cause of a ceiling effect for UR magnitude, even with pleasant pictures. In line with this, emotional state has been shown to modulate airpuff-induced eyeblinks in the case of milder airpuffs (Hawk and Cook, 1997). To conclude, our findings add to the motivational priming hypothesis (Lang et al., 1990) by showing that unpleasant affective states also augment associatively learned defensive responses. Future studies should address the lack of their diminution by pleasant affective states. Acknowledgements The study was funded by a grant from the Academy of Finland to JW (114258). The authors wish to thank Lauri Viljanto for technical help, Dave Lavond for commenting an earlier version of the manuscript and Michael Dutton for revising our English. References Aitken, C.J., Siddle, D.A., Lipp, O.V., 1999. The effects of threat and nonthreat word lead stimuli on blink modification. Psychophysiology 36, 699–705. A˚sli, O., Flaten, M.A., 2007. Conditioned facilitation of the unconditioned reflex after classical eyeblink conditioning. International Journal of Psychophysiology 67, 17–22.
Bonnet, M., Bradley, M.M., Lang, P.J., Requin, J., 1995. Modulation of spinal reflexes: arousal, pleasure, action. Psychophysiology 32, 367–372. Ehrlichman, H., Brown, S., Zhu, J., Warrenburg, S., 1995. Startle reflex modulation during exposure to pleasant and unpleasant odors. Psychophysiology 32, 150–154. Ehrlichman, H., Kuhl, S.B., Zhu, J., Warrenburg, S., 1997. Startle reflex modulation by pleasant and unpleasant odors in a between-subjects design. Psychophysiology 34, 726–729. Grillon, C., 2002. Associative learning deficits increase symptoms of anxiety in humans. Biological Psychiatry 51, 851–858. Hawk, L.W., Cook 3rd, E.W., 1997. Affective modulation of tactile startle. Psychophysiology 34, 23–31. Jansen, D.M., Frijda, N.H., 1994. Modulation of the acoustic startle response by filminduced fear and sexual arousal. Psychophysiology 31, 565–571. Kaviani, H., Gray, J.A., Checkley, S.A., Kumari, V., Wilson, G.D., 1999. Modulation of the acoustic startle reflex by emotionally-toned film-clips. International Journal of Psychophysiology 32, 47–54. Lang, P.J., Bradley, M.M., Cuthbert, B.N., 1990. Emotion, attention and startle reflex. Psychological Review 97, 377–395. Lang, P.J., Bradley, M.M., Cuthbert, B.N., 2001. International affective picture system (IAPS). Instruction manual and affective ratings. Technical report A-5, The Center for research in psychophysiology, University of Florida. Mallan, K.M., Lipp, O.V., 2007. Does emotion modulate the blink reflex in human conditioning? Startle potentiation during pleasant and unpleasant cues in the picture-picture paradigm. Psychophysiology 44, 737–748. Miltner, W., Matjak, M., Braun, C., Diekmann, H., Brody, S., 1994. Emotional qualities of odors and their influence on the startle reflex in humans. Psychophysiology 31, 107–110. Prehn, A., Ohrt, A., Sojka, B., Ferstl, R., Pause, B.M., 2006. Chemosensory anxiety signals augment the startle reflex in humans. Neuroscience Letters 394, 127–130. Steinmetz, J.E., 2000. Brain substrates of classical conditioning: a highly localized but also distributed system. Behavioral Brain Research 110, 13–24. Thompson, R.F., Thompson, J.K., Kim, J.J., Krupa, D.J., Shinkman, P.G., 1998. The nature of reinforcement in cerebellar learning. Neurobiology of Learning and Memory 70, 150–176. Vrana, S.R., Lang, P.J., 1990. Fear imagery and startle-probe reflex. Journal of Abnormal Psychology 99, 189–197.