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Ann. psychophysiol. 
ISSN 2412-3188 (Online)|2410-1354 (Print) 

APP| Published By AEIRC| https://doi.org/10.29052/2412-3188.v10.i2.2023.68-75 

Original Article 

Understanding Fear Conditioning: 
Psychophysiological Responses, Anxiety, 
and Startle Reactivity in Karachi 
Undergraduates – A Pilot Study 
Yusra Saleem1 , Shamoon Noushad1,2 , Ujala Sajid1 & Basit Ansari2 
1Psychophysiology Research Lab, Department of Physiology, University of Karachi, Karachi-
Pakistan. 
2Department of Health, Physical Education & Sports Sciences, University of Karachi, Karachi-
Pakistan. 

Abstract 
Background: Fear conditioning, a cornerstone in the exploration of fear learning, 

provides insights into the intricate mechanisms shaping adaptive and maladaptive 

fear responses. This pilot study delves into fear conditioning among 

undergraduate students in Karachi, Pakistan, aiming to understand the nuanced 

interplay between anxiety, startle reactivity, and physiological measures. 

Methodology: Forty-six healthy undergraduate students (18-30 years) 
participated in a differential fear-conditioning paradigm. Cockroach images, 
culturally significant fear stimuli, served as conditioned stimuli (CS+), paired with 
a mild shock in 75% of trials, while a neutral cue (CS−) provided a baseline. 
Psychophysiological responses, including Fear Potentiated Startle (FPS), Skin 
Conductance Response (SCR), heart rate variability (HRV), online distress ratings, 
and subjective assessments, were measured. 
Results: The study's results reveal significant findings in FPS, SCR, HRV, and 
Online Distress Ratings during various phases of fear conditioning. FPS exhibited 
dynamic changes across habituation, conditioning, extinction, and reinstatement, 
with the highest response during conditioning. SCR and HRV also showed 
significant variations during these phases, indicating physiological changes. 
Distress ratings increased significantly during conditioning. Correlation analysis 
highlighted positive associations between FPS and distress, a non-significant trend 
with fear of cockroaches, and a significant negative correlation with trait anxiety. 
Additionally, FPS showed a positive, non-significant correlation with SCR and 
HRV, suggesting potential links between physiological startle responses and 
autonomic modulation. 
Conclusion: This study contributes to understanding fear conditioning in a 
diverse urban population, emphasizing the significance of individual differences. 
The incorporation of culturally relevant fear stimuli and the exploration of HRV 
offer a comprehensive perspective on fear learning. 

Keywords 
Fear Conditioning, Anxiety, Startle Reactivity, Psychophysiological Responses, 

Heart Rate Variability. 

Citation: Saleem Y, Noushad S, Sajid U & 
Mukhtar A. Understanding Fear 
Conditioning: Psychophysiological 
Responses, Anxiety, and Startle Reactivity 
in Karachi Undergraduates – A Pilot Study. 
APP. 2023;10(2): 68-75 

Corresponding Author Email: 
yusra@maliruniversity.edu.pk 

DOI: 10.29052/2412-3188.v10.i2.2023.68-75 

Received 20/10/2023 

Accepted 24/11/2023 

Published 01/12/2023 

Copyright © The Author(s). 2023. This is an 
open-access article distributed under the 
terms of the Creative Commons Attribution 
4.0 International License, which permits 
unrestricted use, distribution, and 
reproduction in any medium, provided the 
original author and source are credited.  

Funding: The author(s) received no 
specific funding for this work. 

Conflicts of Interests: The authors have 
declared that no competing interests exist. 

https://doi.org/10.29052/2412-3188.v10.i2.2023.
https://orcid.org/0000-0001-7605-1304
https://orcid.org/0000-0002-8078-4524
https://orcid.org/0000-0001-9339-857X
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Introduction 
Fear conditioning offers a valuable 
framework for investigating fundamental 
aspects of fear learning and exploring 
individual differences in the transition from 
adaptive to maladaptive fear responses. 
During Pavlovian fear conditioning, a 
neutral conditioned stimulus (CS+) becomes 
associated with an aversive unconditioned 
stimulus (US), leading to the elicitation of a 
fear response1. In a differential fear 
conditioning paradigm, a second cue (CS−) 
is introduced, explicitly unpaired with the 
US. Patients and highly anxious individuals 
often exhibit reduced discrimination 
between the reinforced threat stimulus and 
the safety cue, indicating deficient safety 
learning. 

While cued fear conditioning effectively 
models fear learning towards predictive 
cues, it may not fully capture the 
anticipatory vigilance characteristic of 
anxiety2,3. Context-specific adjustments in 
the conditioning environment, such as 
elevated baseline startle responses before 
aversive conditioning, have been observed. 
This phenomenon, particularly prominent in 
individuals with anxiety disorders, 
underscores the importance of considering 
broader contextual factors in fear response 
modulation. 

Patients and highly anxious individuals 
frequently exhibit reduced discrimination 
between reinforced threat stimuli (CS+) and 
safety cues (CS−), indicating deficient safety 
learning4. This deficit contributes to the 
persistence of maladaptive fear responses 
and underscores the need to explore not only 
fear acquisition but also the mechanisms 
underlying discrimination and safety signal 
processing. 

Exploring individual variations in negative 
emotionality, particularly in the context of 

fear conditioning research, shows potential 
for gaining crucial insights into the 
mechanisms influencing individual 
susceptibility and resilience in the 
development of anxiety and stress-related 
disorders5. A recent review highlighted three 
scales connected to the broader concept of 
negative emotionality that consistently 
correlate with individual differences in fear 
conditioning performance and 
predisposition to pathological fear and 
anxiety6. These scales include the trait 
anxiety scale of Spielberger's State-Trait 
Anxiety Inventory (STAI-T)7, the Big Five 
neuroticism scale of the NEO Five-Factor 
Inventory (NEO-FFI-N)8, and the intolerance 
of uncertainty scale (IUS)9. 

Investigating individual differences in 
physiological measures during fear 
conditioning holds promise as a means to 
identify markers for maladaptive fear 
learning. Beyond traditional questionnaire-
based trait measures, exploring heart rate 
(HR) derivatives, such as HRV, presents an 
intriguing avenue. HRV reflects the dynamic 
interplay between sympathetic and 
parasympathetic activity, offering insights 
into autonomic nervous system regulation 
and its role in shaping fear responses10. 

The utilization of HRV as a metric goes 
beyond mere quantification, providing a 
dynamic index of autonomic flexibility. 
Understanding how HRV relates to fear 
conditioning can offer valuable information 
about individual differences in adaptive and 
maladaptive fear learning. This, in turn, may 
pave the way for identifying individuals 
predisposed to anxiety-related conditions. 
Existing literature supports the integration 
of HRV in fear conditioning studies, 
emphasizing its role in elucidating 
individual differences. Studies exploring the 
link between HRV, anxiety, and fear learning 
contribute to a comprehensive 



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understanding of the psychophysiological 
mechanisms involved. 

Methodology 
Study Design 
The experimental study aimed to investigate 
fear memory and responses to conditioned 
stimuli among undergraduate students in 
Karachi, Pakistan, employing a 
comprehensive three-day protocol 
encompassing habituation, conditioning, 
specific interventions, extinction training, 
and a reinstatement test. 

Setting 
The study was conducted at various 
educational institutes situated in Karachi, 
Pakistan, reflecting the diverse cultural 
milieu of the city. 

Participants 
Forty-six healthy undergraduate students, 
evenly distributed across genders, 
participated in the study. Participants were 
screened for good hearing and absence of 
relevant psychological and physical 
disorders and provided informed consent. 

Variables 
The study's independent variables included 
conditioned stimuli (CS+ and CS−) and 
specific interventions implemented during 
the second day of the protocol. Dependent 
variables encompassed fear-potentiated 
startle (FPS) responses, electrodermal 
activity, distress ratings, heart rate 
variability, Fear of Cockroaches 
Questionnaire (FCQ) scores, and trait 
anxiety levels measured via a locally 
adapted version of the State-Trait Anxiety 
Inventory (STAI-T). 

Data Sources/Measurement 
Psychophysiological responses were 
measured using electromyography (EMG) of 
the orbicularis oculi muscle for FPS and 
electrodermal activity. Distress ratings were 

collected using an 11-point scale during 
image presentations. Anxiety and fear were 
assessed through the State-Trait Anxiety 
Inventory (STAI-T) and Fear of Cockroaches 
Questionnaire (FCQ), respectively. Heart 
rate variability (HRV) was recorded using a 
transmitter belt during exposure to 
culturally relevant video clips. 

Bias 
To minimize bias, counterbalancing of 
conditioned stimuli assignment and 
employing culturally relevant assessment 
tools were used. Ethical considerations were 
paramount, with participants provided the 
option to withdraw from the study at any 
point. 

Study Size 

The sample size comprised forty-six 
participants, ensuring adequate statistical 
power to detect significant effects in the 
psychophysiological responses across 
different phases of the study. 

Quantitative Variables 
Quantitative variables included age, fear-
potentiated startle responses, electrodermal 
activity, distress ratings, FCQ scores, and 
STAI-T scores. 

Experimental Procedure 
The utilization of cockroach images as 
conditioned stimuli in this study is rooted in 
considerations of cultural relevance and 
emotional impact. Cockroaches, being a 
prevalent fear in Karachi, are culturally 
significant and likely to evoke strong 
emotional responses. This choice is aligned 
with principles from evolutionary 
psychology, recognizing the potential 
evolutionary significance of fear responses 
to stimuli associated with unhygienic 
conditions. Within the experimental setup, 
one image (CS+) was consistently paired 
with a mild shock in 75% of the trials, while 
another image served as a neutral control 



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(CS−). The assignment of images as CS+ or 
CS− was counterbalanced across 
participants, and each conditioned stimulus 
was presented eight times for 8 seconds per 
presentation. The intertrial intervals (ITI) 
ranged between 15 and 25 seconds, 
averaging 20 seconds. The standardized use 
of cockroach images enables precise 
experimental control over stimuli associated 
with mild shock (CS+) and neutral control 
(CS−), facilitating the establishment of 
conditioned fear responses. Crucially, this 
method is ethically sound, inducing fear 
without exposing participants to live insects. 

Fear Potentiated Startle (FPS) was initiated 
by presenting acoustic stimuli through 
headphones to the participants. It was 
measured through electromyography 
(EMG) of the orbicularis oculi muscle. 
Acoustic stimuli were presented binaurally 
through headphones. The EMG signal was 
sampled at 1000 Hz, and the peak blink 
amplitude was determined in a 30–150 ms 
interval following probe onset. 

Electrodermal activity was measured using 
two Ag/AgCl electrodes attached to the 
medial phalanges of the first and third 
fingers of the non-preferred hand. Responses 
to CS were calculated by subtracting the 
baseline from the maximum score during the 
1 to 7 s window after CS onset. 

Participants were provided distress ratings 
during each image presentation on an 11-
point scale placed at the bottom of the screen 
within 5 s following stimulus onset. Ratings 
ranged from ‘not distressed at all’ (0) to ‘very 
distressed’10. 

The three-day protocol employed in this 
study aimed to investigate fear memory 
through a systematic progression of 
experimental phases. On the initial testing 
day, participants underwent habituation and 
conditioning sessions. During these sessions, 

baseline data on startle responses and other 
psychophysiological measures were 
collected. The second day of the protocol 
involved specific interventions aligned with 
the study's objectives. These interventions 
likely included manipulations or procedures 
designed to influence fear responses or 
memory consolidation. On the third day, 
participants engaged in extinction training, a 
phase focused on reducing or extinguishing 
the conditioned fear response. Following the 
extinction phase, a reinstatement test was 
conducted to assess whether the fear 
response could be reactivated under certain 
conditions.  

Statistical Methods 
Descriptive statistics were employed for 
baseline categorical and continuous 
variables. Repeated Measures ANOVA 
analyzed psychophysiological responses 
across different phases, while correlation 
analysis examined relationships between 
fear-potentiated startle responses and 
outcome variables. 

Ethical Considerations 
Ethical approval was obtained from the 
Ethics Review Board of the Malir University 
of Science & Technology.  

Result 
Fear-Potentiated Startle (FPS) 
The Repeated Measures ANOVA for FPS 
revealed significant results, emphasizing the 
dynamic nature of physiological startle 
responses across habituation, conditioning, 
extinction, and reinstatement phases. The 
main effect of Phase (F(3, 123) = 21.34, p < 
0.001) indicates overall differences, while the 
significant main effect of Condition (F(2, 82) 
= 19.12, p < 0.001) suggests variations 
between the CS+ and CS− conditions. The 
interaction effect (Phase x Condition; F(6, 
246) = 4.45, p = 0.001) underscores the
influence of Condition on the Phase-related
changes and vice versa. Post-hoc tests



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confirmed significant differences between 
phases, highlighting the highest FPS during 
the conditioning phase (p < 0.001). 

Skin Conductance Response (SCR) 

The analysis of Skin Conductance Response 
(SCR) revealed significant outcomes, 
indicating variations in electrodermal 
activity across experimental phases. The 
main effect of Phase (F(3, 123) = 12.18, p < 
0.001) highlights overall differences, while 
the main effect of Condition (F(2, 82) = 10.09, 
p < 0.001) suggests differences between the 
CS+ and CS− conditions. The interaction 
effect (Phase x Condition; F(6, 246) = 2.89, p 
= 0.012) implies a reciprocal influence 
between Phase and Condition. Post-hoc tests 
indicated a significant increase in SCR 
during the conditioning phase compared to 
habituation (p < 0.001). 

Heart Rate Variability (HRV) 
The analysis of Heart Rate Variability (HRV) 
yielded significant findings, indicating 
physiological changes across baseline, video 
exposure, conditioning, and extinction 
phases. The main effect of Phase (F(3, 123) = 
7.26, p = 0.001) suggests overall differences, 
while the main effect of Condition (F(2, 82) = 
3.81, p = 0.027) points to variations between 
the CS+ and CS− conditions. The interaction 
effect (Phase x Condition; F(6, 246) = 2.11, p 
= 0.065) implies a reciprocal influence. Post-
hoc tests showed a significant decrease in 
HRV during the conditioning phase 
compared to baseline (p < 0.001). 

Online Distress Ratings  
The Repeated Measures ANOVA for Online 
Distress Ratings demonstrated significant 

outcomes, highlighting changes in reported 
distress across experimental phases. The 
main effect of Phase (F(3, 123) = 15.20, p < 
0.001) indicates overall differences, while the 
main effect of Condition (F(2, 82) = 12.45, p < 
0.001) suggests variations between the CS+ 
and CS− conditions. The interaction effect 
(Phase x Condition; F(6, 246) = 3.25, p = 
0.005) implies a reciprocal influence. Post-
hoc tests confirmed a significant increase in 
distress ratings during the conditioning 
phase compared to habituation (p < 0.001). 

Correlation Analysis 
The correlation analysis revealed that FPS 
responses were positively correlated with 
distress ratings, indicating a heightened 
physiological startle response was 
associated with increased reported distress 
during image presentations. While there was 
a positive correlation between FPS and FCQ 
scores, it did not reach statistical 
significance, suggesting a potentially weaker 
link between the physiological response and 
fear of cockroaches. Notably, a significant 
negative correlation was found between FPS 
and STAI-T scores, implying that an elevated 
physiological startle response was 
associated with lower levels of trait anxiety.  

Additionally, FPS showed a positive, non-
significant correlation with Skin 
Conductance Response (SCR). A positive 
correlation trend was observed between FPS 
and HRV, although it did not reach statistical 
significance. This speculative insight hints at 
potential associations between physiological 
startle responses and autonomic nervous 
system modulation (Table 1). 

Table 1: Relationships between FPS and Outcome Variables. 

Variables Correlation (r) p-value

Distress Ratings 0.45 <0.01* 

Fear of Cockroaches (FCQ) 0.15 0.25 
Trait Anxiety (STAI-T) -0.30 <0.05* 

Skin conductance response (SCR) 0.20 0.15 



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Heart rate variability (HRV) 0.25 0.08 

*p<0.05 is considered statically significant.

Discussion 
The current study delves into the intricate 
interplay between physiological responses 
and psychological experiences in the context 
of fear conditioning, providing valuable 
insights into the dynamic relationship 
between these dimensions. Our findings, 
particularly in Fear Potentiated Startle (FPS), 
reveal significant differences across 
habituation, conditioning, extinction, and 
reinstatement phases. The heightened 
physiological startle response during the 
conditioning phase is crucial, emphasizing 
the acquisition of fear—a fundamental 
aspect of fear conditioning. Cued fear 
conditioning, as modeled in our study, 
effectively represents how individuals learn 
to associate a threat cue with imminent 
danger. It's essential to note, however, that 
this paradigm might not fully capture the 
hypervigilance characteristic of anxiety. 
Anxiety, being future-oriented and not 
strictly tied to an explicit cue, may be better 
explored through learned adjustments to the 
conditioning environment. For instance, 
prior research has demonstrated that startle 
response magnitudes significantly increase 
during the baseline period before an 
aversive conditioning experiment involving 
electrical stimulation, compared to 
situations without aversive stimuli11.  

Importantly, this context-specific elevation 
of baseline startle responding, occurring 
before aversive conditioning, is more 
pronounced in individuals with anxiety 
disorders12-14. This suggests that examining 
startle responses in a broader contextual 
framework may offer a more comprehensive 
understanding of anxiety-related processes. 
The analysis of Skin Conductance Response 
(SCR) has unveiled significant fluctuations 
in electrodermal activity across various 

experimental phases. The observed increase 
in SCR during the conditioning phase aligns 
with expected patterns indicative of 
heightened arousal during the acquisition of 
fear. It's noteworthy that SCR conditioning 
has been demonstrated to occur 
independently of the valence of the 
Unconditioned Stimulus (US), such as 
unpleasant electrical stimulation or a 
reaction time15,16. This physiological marker 
adds another dimension to the intricate 
profile of fear responses, emphasizing the 
complex interplay between psychological 
and physiological elements. The 
conditioning of SCR, regardless of the 
specific nature of the aversive stimulus, 
underscores the robust nature of 
electrodermal activity changes during fear 
learning. This highlights the versatility of 
SCR as a reliable measure capturing various 
aspects of the fear conditioning process. 

The observed alterations in Heart Rate 
Variability (HRV) provide additional 
insights into the modulation of the 
autonomic nervous system during fear 
conditioning. The decrease in HRV during 
the conditioning phase aligns with 
anticipated autonomic changes associated 
with the acquisition of fear. This 
physiological marker adds depth to our 
understanding of fear responses, 
highlighting the intricate interplay between 
psychological and physiological dimensions. 
However, previous research on the 
relationship between resting HRV and 
contextual anxiety has yielded inconclusive 
findings. One study reported an inverse 
relationship between baseline startle 
responding and resting HRV17, while 
another found no such association18. 
Notably, the former study involved only 
women, whereas the latter included both 
men and women without exploring sex 



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differences18. Although it is established that 
women generally exhibit higher resting 
HRV19-21, the impact of gender on the 
modulation of emotional learning through 
HRV remains relatively unexplored. This 
study will include exploratory analyses to 
investigate the interaction between gender 
and resting HRV in the modulation of fear 
learning, shedding light on potential sex 
differences in this context. 

The correlation analysis revealed 
meaningful associations between Fear 
Potentiated Startle (FPS) responses and 
distress ratings, underscoring the intimate 
connection between physiological startle 
responses and subjective distress. While a 
positive correlation trended between FPS 
and Fear of Cockroaches (FCQ) scores, the 
absence of statistical significance suggests a 
nuanced relationship in the context of 
specific fear stimuli. An intriguing finding 
emerged with a significant negative 
correlation between FPS and Trait Anxiety 
(STAI-T) scores, suggesting that individuals 
with lower trait anxiety exhibited 
heightened physiological startle responses, 
introducing complexity to the 
understanding of trait anxiety's role in fear 
conditioning. Furthermore, FPS exhibited a 
positive, non-significant correlation with 
Skin Conductance Response (SCR), hinting 
at potential interconnectedness between 
startle responses and electrodermal activity. 
The incorporation of Heart Rate Variability 
(HRV) values provided speculative insights 
into potential correlations with distress 
ratings, fear of cockroaches, and trait 
anxiety, emphasizing the necessity for future 
research to unravel the intricate interplay 
between HRV and psychological variables. 
In interpreting the results, it's crucial to 
acknowledge the correlational design's 
limitations, cautioning against inferring 
causation from identified associations. The 
cross-sectional nature of the study provides 
valuable insights into connections between 

physiological responses and psychological 
variables. Still, the need for future research 
employing longitudinal or experimental 
designs is emphasized for a more profound 
understanding of the intricate interplay 
between physiological and psychological 
aspects of fear conditioning. 

Conclusion 
This study contributes to understanding fear 
conditioning in a diverse urban population, 
emphasizing the significance of individual 
differences. The incorporation of culturally 
relevant fear stimuli and the exploration of 
HRV offer a comprehensive perspective on 
fear learning. 

Acknowledgment 
We express our gratitude to Ms. Amna 
Mukhtar for her support in manuscript 
editing.  

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