Increase In Pupil Diameter Research Articles

More than a feeling: Scalp EEG and eye signals in conscious tactile perception

Understanding the neural basis of consciousness is a fundamental goal of neuroscience, and sensory perception is often used as a proxy for consciousness in empirical studies. However, most studies rely on reported perception of visual stimuli. Here we present behavior, high density scalp EEG and eye metric recordings collected simultaneously during a novel tactile threshold perception task. We found significant N80, N140 and P300 event related potentials in perceived trials and in perceived versus not perceived trials. Significance was limited to a P100 and P300 in not perceived trials. We also found an increase in pupil diameter and blink rate and a decrease in microsaccade rate following perceived relative to not perceived tactile stimuli. These findings support the use of eye metrics as a measure of physiological arousal associated with conscious perception. Eye metrics may also represent a novel path toward the creation of tactile no-report tasks in the future.

The synergistic efficacy and safety of combined low-concentration atropine and orthokeratology for slowing the progression of myopia: A meta-analysis.

To explore the efficacy and safety of combined low-concentration atropine and orthokeratology (OK) for slowing the progression of myopia. We performed a systematic search of English and Chinese databases to collect potentially eligible randomised controlled trials (RCTs), nonrandomised controlled trials (non-RCTs) and retrospective cohort studies (REs) published between the establishment of the database and 1 January 2022. The weighted mean difference (WMD) and 95% confidence interval (CI) were calculated for each outcome. Fifteen studies were ultimately included in the meta-analysis, which indicated that compared with OK lenses alone, the combination of low-concentration atropine with OK lenses significantly slowed axial growth (WMD=-0.12 mm; 95% CI: -0.13 to -0.11, p < 0.001) and reduced the rate of change of the spherical equivalent refraction (WMD=0.15 D; 95% CI: 0.06 to 0.24, p < 0.001). Additionally, the combined treatment may cause a slight increase in pupil diameter (WMD=0.62 mm; 95% CI: 0.42 to 0.81, p < 0.001). No significant difference in the amplitude of accommodation, intraocular pressure, tear film break-up time or corneal endothelial cell density was found between the OK and combination therapy groups. The combination therapy of low-concentration atropine and OK lenses had a greater effect in slowing myopia progression during a 6-to-12-month treatment interval and was still effective over a 24-month period. Increased pupil diameter was the major side effect of the combination therapy, with no negative impact on the amplitude of accommodation, intraocular pressure, tear film break-up time or corneal endothelial cell density.

Do pupillary responses during authentic slot machine use reflect arousal or screen luminance fluctuations? A proof-of-concept study.

Modern slot machines are among the more harmful forms of gambling. Psychophysiological measures may provide a window into mental processes that underpin these harms. Here we investigated pupil dilation derived from eye tracking as a means of capturing changes in sympathetic nervous system arousal following outcomes on a real slot machine. We hypothesized that positively reinforcing slot machine outcomes would be associated with increases in arousal, reflected in larger pupil diameter. We further examined the contribution of game luminance fluctuations on pupil diameter. In Experiment 1A, experienced slot machine gamblers (N = 53) played a commercially-available slot machine in a laboratory for 20 minutes while wearing mobile eye tracking glasses. Analyses differentiated loss outcomes, wins, losses-disguised-as-wins, and (free-spin) bonus features. Bonus features were associated with rapid increases in pupil diameter following the onset of outcome-related audiovisual feedback, relative to losses. In Experiment 1B, luminance data were extracted from captured screen videos (derived from Experiment 1A) to characterize on-screen luminance changes that could modulate pupil diameter. Bonus features and wins were associated with pronounced and complex fluctuations in screen luminance (≈50 L and ≈25L, respectively). However, the pupil dilation that was observed to bonus features in Experiment 1A coincided temporally with only negligible changes in screen luminance, providing partial evidence that the pupil dilation to bonus features may be due to arousal. In Experiment 2, 12 participants viewed pairs of stimuli (scrambled slot machine images) at luminance difference thresholds of ≈25L, ≈50L, and ≈100L. Scrambled images presented at luminance differences of ≈25L and greater were sufficient to cause pupillary responses. Overall, pupillometry may detect event-related changes in sympathetic nervous system arousal following gambling outcomes, but researchers must pay careful attention to substantial in-game luminance changes that may confound arousal-based interpretations.

Pupil response to painful stimuli during inhalation anaesthesia without opioids in children.

Pupil dilation reflex measured by a pupillometer is known to be a useful parameter for assessing the response to perioperative noxious stimuli. In children, pupillometer can reflect changes after painful stimuli during anaesthesia or guide anaesthesia to reduce opioid consumption. However, to date, there are no data regarding pupil response during inhalation anaesthesia with analgesia by intravenous acetaminophen in children. We planned a prospective, single-armed study of children aged between 3 and 12 years who underwent surgery under general anaesthesia. Anaesthesia was maintained by 1 minimum alveolar concentration (MAC) of sevoflurane, and 15 mg/kg of acetaminophen was administered. Patients' left eye was examined using a pupillometer after induction, before and after skin incision and train-of-four stimulus. Pupil diameter and other pupillometric parameters were recorded. Increase in heart rate by 15% was regarded as insufficient analgesia to skin incision and indicative powers of pupillometric parameters for insufficient analgesia were examined by receiver-operating characteristics. A total of 33 patients were included. Enlarged pupil, large increase in pupil diameter and low neurological pupil index (NPi) after skin incision were good indicators of insufficient analgesia for skin incision. Children with insufficient analgesia showed abnormal NPi value. However, increase in pupil diameter and decrease in NPi were observed even in patients without increase in the heart rate after the skin incision. We suggest dilation of the pupil and decrease in NPi can indicate response to noxious stimuli in children. Regardless of sufficiency of analgesia, pupil dilation and decrease in NPi were observed after skin incision in children under general anaesthesia with 1 MAC of sevoflurane and intravenous acetaminophen.

P 22 Effects of multisensory feedback on tremor severity in essential tremor

Introduction : Essential tremor (ET) amplitude is modulated by visual feedback during target-driven movements: In a grip force task, tremor amplitude increases during large-scale visual feedback compared to low-scale visual feedback. It has not been examined whether visual feedback exclusively modulates action tremor severity or if an increase of other afferent input like auditory information has a modulatory effect on tremor amplitude as well. Also, it is unknown whether the sensory signal itself directly affects the tremor generating network or if the effect is rather indirect: enhanced sensory feedback during targeted driven movements might cause arousal/psychological stress. We hypothesized that (1) amplitude of ET is modulated by variation of auditory feedback in the absence of visual feedback in a force tremor paradigm; (2) increase of tremor amplitude coincides with pupillary dilation as a measure of arousal / psychological stress, independently of the quality of sensory feedback Patients & Methods : 14 ET patients conducted a computer-based experiment in which they were asked to match a target force in a force sensor using their thumb and index finger. The quality of them matching the target force was fed back to the participant visually, auditory or a combination of both. For the visual feedback, 2 bars were displayed on a screen, with the distance between these bars decreasing with approximation of the target force. In auditory feedback, a target tone of 440Hz was asked to match by a second tone which changed pitch when approximating the target force. The amplitude of feedback was manipulated via a scaling factor resulting in a large scale and a small scale feedback condition. To characterize the performance (RMSE to target force) and the tremor severity (Power 4-12 Hz) a 3x2 ANOVA was conducted. To control for arousal / psychological stress-induced via the task, pupillometry was recorded. Results : First results showed a comparable deviation from the target force (RMSE) during the experiment in all three sensory feedback modalities. Additionally, tremor severity did not differ between sensory feedback modalities. The ANOVA revealed an effect of the scaling factor on the tremor severity (Power 4-12Hz) for the visual and also for the auditory feedback condition. Pupillometry consistently showed a significantly increased pupil diameter during the large-scale visual- and auditory feedback conditions compared to the small-scale feedback conditions. Conclusion : Our preliminary findings suggest that action tremor in ET is firstly modulated not only by visual but also auditory feedback in a comparable manner and seems to be modality independent. Secondly, arousal / cognitive stress, as measured here by the pupil size, could mediate the increase of tremor amplitude. Further work is required better understand the role of these two possible mechanisms underlying target-related tremor.

Study of the effect of adding topical Nepafenac 0.1% eye drop on increasing mydriasis in patients with diabetes mellitus type 2

Objective: To evaluate the effect of adding topical Nepafenac 0.1% eye drop on increasing mydriasis in patients with Diabetes Mellitus type 2. Methods: the study was conducted on 73 eyes of 73 patients who had type 2 diabetes for 5 years or more. The pupil diameter (PD) was measured in the both eyes without dilation using an Autorefractokeratometer (Grand Seiko\GR- 3500 Ka), then the pupils were dilated in the both eyes using topical Tropicamide 1%. A second measurement of (PD) was taken after dilating using the same device. Topical Nepafenac 0.1% were prescribed 3 times a day for 3 days in the right eye. During the review, after 3 days, the pupils were dilated using topical Tropicamide 1%. A third measurement of the (PD) of the both eyes was taken after dilation using the same device. The efficacy of Nepafenac 0.1% was evaluated by determining the increase in (PD) in the eye that received topical Nepafenac 0.1% and comparing it with the other eye that did not receive. Results: The mean diameter of the pupil in the right eye after dilation was 4.68±0.8 mm and in the left eye was 4.67±0.7 mm (P=0.8). After applying Nepafenac 0.1% topically 3 times a day in the right eye for 3 days, the mean diameter of the pupil in the right eye after dilation was 6.50 ± 0.9 mm and in the left eye 5.10± 0.08 mm (P=0.001). The change in the mean diameter of the pupil in the right eye was 1.82 ± 0.7 mm, and in the left eye was 0.43 ± 0.6 mm. Conclusion: Topical application of Nepafenac 0.1% showed an increase in pupillary diameter after dilation with Tropicamide 1% in patients with type 2 diabetes mellitus.

Publication guidelines and recommendations for pupillary measurement in psychophysiological studies.

A variety of psychological and physical phenomena elicit variations in the diameter of pupil of the eye. Changes in pupil size are mediated by the relative activation of the sphincter pupillae muscle (decrease pupil diameter) and the dilator pupillae muscle (increase pupil diameter), innervated by the parasympathetic and sympathetic branches, respectively, of the autonomic nervous system. The current guidelines are intended to inform and guide psychophysiological research involving pupil measurement by (1) summarizing important aspects concerning the physiology of the pupil, (2) providing methodological and data-analytic guidelines and recommendations, and (3) briefly reviewing psychological phenomena that modulate pupillary reactivity. Because of the increased ease and tractability of pupil measurement, the goal of these guidelines is to promote accurate recording, analysis, and reporting of pupillary data in psychophysiological research.

Visual performance with multifocal lenses in young adults and presbyopes.

A better understanding of visual performance with Multifocal Contact Lenses (MCLs) is essential, both in young eyes, where MCLs may be prescribed to control the progression of myopia wherein the MCLs optics interact with accommodation, and in presbyopes, where MCLs are increasingly used to compensate the lack of accommodation. In this study, we evaluated the through focus visual acuity (TFVA) with center-near MCLs of three additions (low, medium and high) and without an addition (NoLens) in 10 young adults and 5 presbyopes. We studied the effect of accommodation, age and pupil diameter (in cyclopleged subjects) on visual performance. The MCLs produced a small but consistent degradation at far (by 0.925 logMAR, averaged across eyes and conditions) and a consistent benefit at near in young subjects with paralyzed accommodation (by 1.025 logMAR), and in presbyopes with both paralyzed and natural accommodation (by 1.071 logMAR, on average). TFVA in young adults with NoLens and all MCLs showed statistically significant differences (Wilcoxan, p<0.01) between natural and paralyzed accommodation, but not in presbyopes with MCLs. In young adults, VA improved with increasing pupil diameter with the HighAdd MCL (0.08 logMAR shift from 3 to 5-mm pupil size). Visual imbalance (standard deviation of VA across distances) was reduced with MCLs, and decreased significantly with increasing near add. The lowest imbalance occurred in young adults under natural accommodation and was further reduced by 13.33% with MCLs with respect to the NoLens condition. Overall, the visual performance with MCLs in young adults exceeds that in presbyopes at all distances, and was better than 0.00 logMAR over the dioptric range tested. In conclusion, the center-near lenses do not degrade the near high contrast visual acuity significantly but maintains the far vision in young adults, and produce some visual benefit at near in presbyopes.

Pupil Dilation Response to Prosody and Syntax During Auditory Sentence Processing.

Pupil dilation response has been shown to reflect different levels of sentence processing during prosodic and syntactic processing in language comprehension. Our pupillometry experiment aimed to investigate whether pupil diameter was sensitive to the auditory sentence processing involved in comprehending congruent and incongruent statements. Twenty-one participants were presented with 300 auditory stimuli consisting of syntactically and/or prosodically congruent and incongruent sentences in Turkish. The pupillary response results were significant only for syntactically incongruent sentences and for sentences that were both syntactically and prosodically incongruent. This indicates that prosody had no significant effect on its own. Based on the hypothesis that prosodic and syntactic processing require cognitive sensitivity for auditory sentence comprehension, we expected an increase in pupil diameter for both processes. However, our findings are consistent with the previous assumptions that pupil size increases during syntactic manipulation, but our findings showed that prosodic processing does not increase pupil size, contrary to previous studies.

Attentional and meta-cognitive processes underlying mind wandering episodes during continuous naturalistic reading are associated with specific changes in eye behavior.

Although eye movements during reading have been studied extensively, their variation due to attentional fluctuations such as spontaneous distractions is not well understood. Here we used a naturalistic reading task combined with an attentional sampling method to examine the effects of mind wandering-and the subsequent metacognitive awareness of its occurrence-on eye movements and pupillary dynamics. Our goal was to better understand the attentional and metacognitive processes involved in the initiation and termination of mind wandering episodes. Our results show that changes in eye behavior are consistent with underlying independent cognitive mechanisms working in tandem to sustain the attentional resources required for focused reading. In addition to changes in blink frequency, blink duration, and the number of saccades, variations in eye movements during unaware distractions point to a loss of the perceptual asymmetry that is usually observed in attentive, left-to-right reading. Also, before self-detected distractions, we observed a specific increase in pupillary diameter, indicating the likely presence of an anticipatory autonomic process that could contribute to becoming aware of the current attentional state. These findings stress the need for further research tackling the temporal structure of attentional dynamics during tasks that have a significant real-world impact.

Comparison of pupillary diameter variation between conventional phacoemulsification versus femtosecond laser-assisted cataract surgery

Purpose: To evaluate and compare variations in pupillary diameter before and after cataract surgery by conventional phacoemulsification versus femtosecond laser assisted cataract surgery, using LDV Z8 (Ziemer Ophthalmic). We also evaluated the relationship between pupillary diameter and surgery time and ultrasound time. Methods: Prospective comparative study, carried out at the Center of Excellence in Ophthalmology, Brazil. We included 79 eyes of 67 patients with nuclear opacity. The patients were divided into the control and study groups, including those who underwent cataract surgery with manual phacoemulsification, and femtosecond laser assisted cataract surgery, respectively. All surgeries were performed by the same experienced surgeon. All patients received topical non-steroidal anti-inflammatory drugs on the day before surgery and the same mydriatic eye drops preoperatively. To quantify pupillary size, measurements were performed using a surgical compass: anterior to the phacoemulsification procedure and at the end of the surgery. In the study group, measurements after laser were added. Surgical time and phacoemulsification time were also analyzed. Results: No significant difference was found between the pre-femto × pre-phaco pupil size (8.69 ± 0.44 mm × 8.63 ± 0.72 mm; p=0.643), and the pupil size at the end of surgery (7.96 ± 0.98 mm × 7.78 ± 0.95 mm; p=0.480) and the mean time of surgery (p=0.780). However, in the femtosecond laser assisted cataract surgery group, a transient increase in pupillary diameter after laser treatment was observed, indicating a tendency for greater variation in the femto group. Conclusions: Although pupil size diameter was similar at the end of surgery, the femtosecond laser assisted cataract surgery group presented higher intraoperative pupil variation. The surgeon should be aware of pupil size diameter before surgery for better and safer performance of femtosecond laser assisted cataract surgery.

The effect of autonomic nervous system tone on the content of cyclic and acyclic aminoacids in the serum of chickens

Regulation of metabolic and physiological functions of the whole organismis a complex neurohumoral process. Its functioning is supported by many organs and systems. One of the main roles here is performed by the autonomic nervous system. The mutual influence of its departments – sympathetic and parasympathetic, provide stable homeostasis and balanced work of all organs and structures. The sympathetic department is responsible for energy resource mobilization and adaptation. Without its influence, a rapid response of the cardiovascular and endocrine systems to the body's needs arising from changes in the internal or external environment is impossible. Dominant sympathetic tone provides activation of gluconeogenes is and glycogenolysis, lipolysis, etc. In contrast, the parasympathetic division is responsible for energy conservation and nutrient accumulation. Its dominant activity causes a decrease in heart rate, increase in pupil diameter depending on light flux, secretion of saliva and digestive juices, acceleration of motility of the gastrointestinal tract. However, to date, the existence of the influence of the tone of the autonomic nervous system on the content of proteins and their derivatives in the serum has not been studied enough. Proteins and their main components – aminoacids are indispensable in the construction and functioning of the whole organism of all living beings. Deficiency or absence of at least one essential amino acid can lead to disruption of various functional systems of the body, adverse health effects, and in the case of long-term deficiency and death. Studies to determine the content of amino acids in the serum of chickens with different dominant tone of the autonomic nervous system revealed different contents of individual cyclic and acyclic amino acids. The content of phenylalanine in sympathicotonic chickens differed significantly compared with the bird, which had a balanced tone (P˂0.05). In contrast, the tyrosine content was almost the same in all groups of animals. The amino acids leucine/ isoleucine and alanine were not significantly predominant in the different samples, but tended to be higher in sympathetic and vagotonic chickens. The study suggests that the dominance of the sympathetic and parasympathetic divisions of the autonomic nervous system or their balanced tone on the content of amino acids in the serum of chickens. Key words: sympathicotonia, vagotonia, normotony, phenylalanine, alanine, leucine/isoleucine, tyrosine.

Influence of visual food cues on autonomic activity and craving

In this study, we tested the hypothesis that autonomic control of the stomach is related to craving and is modulated by visual food cues. Twenty-nine healthy human participants were shown pictures of either high- or low-appeal food, as well as non-food pictures, and were asked to rate how much they wanted to eat each item using a 7-point Likert scale. Simultaneously, the electrogastrogram, electrocardiogram, electrodermal activity, respiration rate, and pupil diameter were recorded. After the ingestion of a 500-kcal liquid meal, participants were asked to perform the task a second time. Despite changes in craving ratings, we did not find changes in the amplitude of the gastric rhythm, but we found increases in pupil diameter for the high appeal food pictures. Moreover, craving ratings were mostly related to increases in pupil and tonic electrodermal activity, compatible with an increase in arousal and a heightened motivational response to food.

Pupil dilation predicts individual self-regulation success across domains

Multiple theories have proposed that increasing central arousal through the brain’s locus coeruleus—norepinephrine system may facilitate cognitive control and memory. However, the role of the arousal system in emotion regulation is less well understood. Pupil diameter is a proxy to infer upon the central arousal state. We employed an emotion regulation paradigm with a combination of design features that allowed us to dissociate regulation from emotional arousal in the pupil diameter time course of 34 healthy adults. Pupil diameter increase during regulation predicted individual differences in emotion regulation success beyond task difficulty. Moreover, the extent of this individual regulatory arousal boost predicted performance in another self-control task, dietary health challenges. Participants who harnessed more regulation-associated arousal during emotion regulation were also more successful in choosing healthier foods. These results suggest that a common arousal-based facilitation mechanism may support an individual’s self-control across domains.

More mental rotation time does not imply more mental effort: Pupillary diameters do not change with angular distance

The ability to mentally rotate objects in space is a fundamental cognitive capacity. Previous studies showed that the time to rotate the image of a figure to match another increases progressively with angular disparity. It remains unclear whether this increase in response time with angular disparity could reflect increased processing operations or more cognitive effort instead of a sustained use of a ‘rotate’ mechanism without a change in workload. We collected response times as well as pupillary responses that index cognitive workload and activity in the brainstem’s locus coeruleus, from a sample of 38 young adults performing a chronometric mental rotations task. The results showed the expected increase in response times but no increase in pupil diameters between 60, 120, and 180 degrees of rotation, suggesting no significant changes in arousal levels when rotating figures near and far. This indicates that during mental rotation the load on cognitive resources remains constant irrespective of angular distance.

Brightness perception changes related to pupil size

Dilating the pupils allow more quanta of light to impact the retina. Consequently, if one pupil is dilated with a pharmacological agent (Tropicamide), the brightness of a surface under observation should increase proportionally to the pupil dilation. Little is known about causal effects of changes in pupil size on perception of an object’s brightness. In a psychophysical procedure of brightness adjustment and matching, we presented to one eye geometrical patterns with a central square (the reference pattern) that differed in physical brightness within backgrounds of constant luminance. Subsequently, with the other eye, participants (n = 30) adjusted to the same luminance a similar pattern (target) whose central square luminance was randomly set higher or lower in brightness than the reference. As only one eye was treated with Tropicamide, we assessed whether the subjective brightness of the target square shifted in a consistent direction when viewed with the dilated pupil compared to the untreated (control) eye. We found that, as the pupil increased post drug administration, so significantly did the sense of brightness of the pattern (i.e., higher brightness adjustments followed viewing the reference pattern with the treated (Tropicamide) eye). A reversed effect was observed when the control eye viewed the reference pattern first. The results confirm that even slight pupil dilations can result in an enhanced perceptual experience of brightness of the attended object, corresponding to an average increase of 2.09 cd/m2 for each 1 mm increase in pupil diameter.

A multimodal study to measure the cognitive demands of hazard recognition in construction workplaces

Hazard recognition has been extensively explored in previous studies. However, deficits have arisen due to the neglect of task-specific effects, information distortion by image-based experimental tasks, and the exclusive use of eye trackers. This study aimed to explore how cognitive patterns vary in simulated construction worksites with different types of hazards using multimodal monitoring. A hazard recognition task was conducted in a hazardous civil laboratory using both an eye tracker and a near-infrared spectrum system to capture pupil responses and cerebral oxyhemoglobin signals. Cognitive responses were analyzed according to hazard type and scene complexity. The results showed that falling hazards induced the most cerebral and pupillary activation. Scene complexity triggers an increase in pupil diameter and impacts cerebral activities by interaction with hazard type. This study also reveals the complementary functions of pupillary responses and neural processes in hazardous simulated worksites and a ceiling effect of cognitive resources. We conclude that construction workplaces with different types of hazards can induce different cognitive demands and should thus be treated individually. This information is potentially useful for practical applications.

Damage to Orbitofrontal Areas 12 and 13, but Not Area 14, Results in Blunted Attention and Arousal to Socioemotional Stimuli in Rhesus Macaques.

An earlier study in monkeys indicated that lesions to the mid-portion of the ventral orbitofrontal cortex (OFC), including Walker’s areas 11 and 13 (OFC11/13), altered the spontaneous scanning of still pictures of primate faces (neutral and emotional) and the modulation of arousal. Yet, these conclusions were limited by several shortcomings, including the lesion approach, use of static rather than dynamic stimuli, and manual data analyses. To confirm and extend these earlier findings, we compared attention and arousal to social and nonsocial scenes in three groups of rhesus macaques with restricted lesions to one of three OFC areas (OFC12, OFC13, or OFC14) and a sham-operated control group using eye-tracking to capture scanning patterns, focal attention and pupil size. Animals with damage to the lateral OFC areas (OFC12 and OFC13) showed decreased attention specifically to the eyes of negative (threatening) social stimuli and increased arousal (increased pupil diameter) to positive social scenes. In contrast, animals with damage to the ventromedial OFC area (OFC14) displayed no differences in attention or arousal in the presence of social stimuli compared to controls. These findings support the notion that areas of the lateral OFC are critical for directing attention and modulating arousal to emotional social cues. Together with the existence of face-selective neurons in these lateral OFC areas, the data suggest that the lateral OFC may set the stage for multidimensional information processing related to faces and emotion and may be involved in social judgments.

Increased pupil diameter is a protective factor against intraoperative floppy‐iris syndrome

Chang and Campbell were the first authors to describe intraoperative floppy‐iris syndrome (IFIS) in 2005 as a syndrome affecting patients undergoing routine phacoemulsification who present with a t...

The effect of oxytocin on pupil response to naturalistic dynamic facial expressions

The neuropeptide oxytocin (OT) has been found to play an important role in a variety of social behaviours and social cognition in particular. The social salience hypothesis of OT suggests that OT shifts attention towards socially relevant stimuli, which offers an explanation for improvements on social cognition measures following OT administration. Pupil dilation occurs with increasing attentional resource allocation and previous research has found that OT administration led to an increase in pupil diameter in response to social stimuli relative to placebo (PL), thereby suggesting increased social attention. The current study aimed to investigate the effects of OT on pupillary responses to more naturalistic social stimuli in a larger sample. Ninety-four male participants took part in the double-blind, placebo controlled, mixed-design study, in which they self-administered either an OT or PL nasal spray before viewing naturalistic dynamic facial expressions of emotion (happy, sad, fear and anger). Contrary to prediction, there was no effect of OT administration on pupil diameter. The results are discussed in light of the social salience hypothesis and with reference to the methodological differences between studies.