Investigating causal effects of pupil size on visual discrimination and visually evoked potentials in a Snellen eye chart task

Investigating causal effects of pupil size on visual discrimination and visually evoked potentials in a Snellen eye chart task | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Investigating causal effects of pupil size on visual discrimination and visually evoked potentials in a Snellen eye chart task Hsin-Hua Chin, Ying-Hsuan Tai, Rachel Yep, Yi-Hsuan Chang, Chun-Hsien Hsu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3412790/v2 This work is licensed under a CC BY 4.0 License Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Abstract Pupil size primarily changes to regulate the amount of light entering the retina, optimizing the balance between visual acuity and sensitivity for effective visual processing. However, research directly examining the relationship between pupil size and visual processing has been limited. While a few studies have recorded pupil size and EEG signals to investigate the role of pupil size in visual processing, these studies have predominantly focused on the domain of visual sensitivity. Causal effects of pupil size on visual acuity, therefore, remain poorly understood. By manipulating peripheral background luminance levels and target stimulus contrast while simultaneously recording pupillometry and EEG signals, we examined how absolute pupil size impacts visual discrimination and visually evoked potentials (VEP) in a task mimicking the Snellen eye chart, the most common assessment of visual acuity. Our findings indicate that both higher background luminance levels and higher target contrast were associated with improved target discrimination and faster correct reaction times. Moreover, while higher contrast visual stimuli evoked larger VEPs, the effects of pupil size on VEPs were not significant. Additionally, we did not observe inter-individual correlations between absolute pupil size and discrimination performance or VEP amplitude. Together, our results demonstrate that absolute pupil size, regulated by global luminance level, played a functional role in enhancing visual discrimination performance in a Snellen eye chart task. The differential VEP effects of pupil size compared to those of stimulus contrast further suggested distinct neural mechanisms involved in facilitating visual acuity under small pupils. Biological sciences/Neuroscience/Oculomotor system Biological sciences/Neuroscience/Sensorimotor processing Biological sciences/Psychology/Human behaviour pupillometry visual discrimination visual sensitivity visuocortical activity pupil light reflex Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Full Text Additional Declarations The authors declare no competing interests. Supplementary Files SupplementaryFigures.docx Cite Share Download PDF Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3412790","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":239176971,"identity":"8aff3de1-0a29-4722-8e7d-01a4bbe756d4","order_by":0,"name":"Hsin-Hua Chin","email":"","orcid":"","institution":"Shuang Ho Hospital, Taipei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Hsin-Hua","middleName":"","lastName":"Chin","suffix":""},{"id":239176972,"identity":"d57de50f-45d2-494a-a8dc-353603357a91","order_by":1,"name":"Ying-Hsuan Tai","email":"","orcid":"","institution":"Taipei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Ying-Hsuan","middleName":"","lastName":"Tai","suffix":""},{"id":239176973,"identity":"368e26d2-1bac-4ec7-8fd4-175ff2fdc827","order_by":2,"name":"Rachel Yep","email":"","orcid":"","institution":"University of Toronto","correspondingAuthor":false,"prefix":"","firstName":"Rachel","middleName":"","lastName":"Yep","suffix":""},{"id":272972390,"identity":"3304dbdc-ac19-4ca0-bc87-0fd5d48ac970","order_by":3,"name":"Yi-Hsuan Chang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yi-Hsuan","middleName":"","lastName":"Chang","suffix":""},{"id":272972391,"identity":"0e0746ca-e40b-4dea-b650-3b781d42b171","order_by":4,"name":"Chun-Hsien Hsu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Chun-Hsien","middleName":"","lastName":"Hsu","suffix":""},{"id":239176974,"identity":"50551ec1-8f49-40b3-b796-24f7f79f509b","order_by":5,"name":"Chin-An Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYBACxgYGNgiLvQEmQLQWnsMwAWaCFkG1SCQTqYW5vf3ZA8Y2uzz5yPdHN/Mw2MhuOMB/TAKvw3rOmBswtiUXG95OZrvNw5BmvOEAMxt+LTNy2CQYtzEnbpwN1nI4EaTlBn4t6c+AWuoTN848DNLynxgtCWZALYcT50swg7QcIEJLzxkzicR/xxM38CSb3ZxjkGw88zCz+Q98WgyBISbx4Ux14vz2g89uvKmwk+073vjYAK+WBiCRAMQGB0BckFpCMSkPZzQQUDkKRsEoGAUjFwAAyupK599IrpsAAAAASUVORK5CYII=","orcid":"","institution":"Taipei Medical University","correspondingAuthor":true,"prefix":"","firstName":"Chin-An","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2023-10-05 09:44:26","currentVersionCode":2,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-3412790/v2","doiUrl":"https://doi.org/10.21203/rs.3.rs-3412790/v2","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":51192770,"identity":"021e385a-49f3-4d42-a5ee-757a65afe81e","added_by":"auto","created_at":"2024-02-15 17:32:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":26052,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExperimental paradigm. \u003c/strong\u003eEach trial began with the appearance of a central FP within a large white circle (151 cd/m\u003csup\u003e2\u003c/sup\u003e) on one of three possible background luminance levels (Bright: 137 cd/m\u003csup\u003e2\u003c/sup\u003e; Mid: 36 cd/m\u003csup\u003e2\u003c/sup\u003e; Dark: 0.1 cd/m\u003csup\u003e2\u003c/sup\u003e). After a delay, the central FP was removed for 100 ms (gap) before the optotype target stimulus. Participants were required to report the orientation of the optotype stimulus using the four arrow keys (Up, Down, Left, Right) on a keyboard. Note that the optotype stimulus shown here is for illustration purposes only.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/08b8b1b4c2329ef6bb7d18c9.png"},{"id":51192771,"identity":"49091f9e-60ae-483a-bb7b-53a24111cb48","added_by":"auto","created_at":"2024-02-15 17:32:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":176452,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of background luminance on absolute pupil size. \u003c/strong\u003eAbsolute pupil diameter following target appearance for each background luminance level (A). Mean absolute pupil diameter (-50 to 50 ms after optotype target onset) shown for the different contrast conditions and background luminance levels (B). In A, the shaded colored regions surrounding the pupillary response curves represent the ± standard error range (across participants). The target epoch is shaded in gray. In B, the large squares and error bars represent the mean values ± standard error across participants. The small dots represent the mean value for each participant. High: high target visual contrast, Low: low target visual contrast. * indicates statistically significant.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/5758acd9464f401bfd2eda21.png"},{"id":51192772,"identity":"b2a423e5-2eba-4722-95c0-6ecc7ad6ed64","added_by":"auto","created_at":"2024-02-15 17:32:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":185796,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of background luminance and target contrast on task accuracy and reaction time. \u003c/strong\u003eDiscrimination accuracy (A) and reaction time (B) shown for different target contrast conditions and background luminance levels. The large squares and error bars represent the mean values ± standard error across participants. The small dots represent the mean value for each participant. High: high target visual contrast, Low: low target visual contrast. * indicates statistically significant.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/8e4c0ff1098b12e6346fc2a6.png"},{"id":51193195,"identity":"37c27aaa-f8aa-40a1-b17d-70c6462d306e","added_by":"auto","created_at":"2024-02-15 17:40:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":238333,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of baseline-corrected pupil dilation on task performance. \u003c/strong\u003eBaseline-corrected pupil size following target appearance for each background luminance level (A). Mean pupil dilation (-50 to 50 ms after target onset) shown for the different contrast conditions and background luminance levels(B). In A, the shaded colored regions surrounding the pupillary response curves represent the ± standard error range (across participants). The target epoch in which mean pupil dilation was calculated is shaded in gray. In B, the large squares and error bars represent the mean values ± standard error across participants. The small dots represent the mean value for each participant. High: high target visual contrast, Low: low target visual contrast.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/62bbb1e3afaecced4a7041c9.png"},{"id":51192774,"identity":"c2e77d0d-800c-4954-8dd3-c42d111b5721","added_by":"auto","created_at":"2024-02-15 17:32:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":168498,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eInter-individual correlation between absolute pupil size and task performance. \u003c/strong\u003eInter-individual correlations between absolute pupil size and accuracy for each background luminance level (A), and between absolute pupil size and reaction time for each background luminance level(B). Colored lines indicate regression lines. The small dots represent the mean value for each participant. High: high target visual contrast, Low: low target visual contrast.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/a352f387c87d3a1d22f30925.png"},{"id":51193828,"identity":"0cf76006-e440-4b91-90fe-73a7534b0475","added_by":"auto","created_at":"2024-02-15 17:56:11","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1167736,"visible":true,"origin":"","legend":"","description":"","filename":"PupilOptoBkgd20240211bsub.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2_covered_f6191037-a42c-4f51-a5d0-7b6424d2917f.pdf"},{"id":51192775,"identity":"12f8fcd8-a301-4154-898a-646c446b6095","added_by":"auto","created_at":"2024-02-15 17:32:03","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":185410,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-3412790/v2/e601ac391120e998f451d77f.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eInvestigating causal effects of pupil size on visual discrimination and visually evoked potentials in a Snellen eye chart task\u003c/p\u003e","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"pupillometry, visual discrimination, visual sensitivity, visuocortical activity, pupil light reflex","lastPublishedDoi":"10.21203/rs.3.rs-3412790/v2","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3412790/v2","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePupil size primarily changes to regulate the amount of light entering the retina, optimizing the balance between visual acuity and sensitivity for effective visual processing. However, research directly examining the relationship between pupil size and visual processing has been limited. While a few studies have recorded pupil size and EEG signals to investigate the role of pupil size in visual processing, these studies have predominantly focused on the domain of visual sensitivity. Causal effects of pupil size on visual acuity, therefore, remain poorly understood. By manipulating peripheral background luminance levels and target stimulus contrast while simultaneously recording pupillometry and EEG signals, we examined how absolute pupil size impacts visual discrimination and visually evoked potentials (VEP) in a task mimicking the Snellen eye chart, the most common assessment of visual acuity. Our findings indicate that both higher background luminance levels and higher target contrast were associated with improved target discrimination and faster correct reaction times. Moreover, while higher contrast visual stimuli evoked larger VEPs, the effects of pupil size on VEPs were not significant. Additionally, we did not observe inter-individual correlations between absolute pupil size and discrimination performance or VEP amplitude. Together, our results demonstrate that absolute pupil size, regulated by global luminance level, played a functional role in enhancing visual discrimination performance in a Snellen eye chart task. The differential VEP effects of pupil size compared to those of stimulus contrast further suggested distinct neural mechanisms involved in facilitating visual acuity under small pupils.\u003c/p\u003e","manuscriptTitle":"Investigating causal effects of pupil size on visual discrimination and visually evoked potentials in a Snellen eye chart task","msid":"","msnumber":"","nonDraftVersions":[{"code":2,"date":"2024-02-15 17:31:57","doi":"10.21203/rs.3.rs-3412790/v2","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}},{"code":1,"date":"2023-10-10 18:28:17","doi":"10.21203/rs.3.rs-3412790/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"845a7591-983b-4e4f-b20f-b11b3163d65c","owner":[],"postedDate":"February 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":28787083,"name":"Biological sciences/Neuroscience/Oculomotor system"},{"id":28787084,"name":"Biological sciences/Neuroscience/Sensorimotor processing"},{"id":28787085,"name":"Biological sciences/Psychology/Human behaviour"}],"tags":[],"updatedAt":"2023-10-21T04:14:09+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-15 17:31:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v2","identity":"rs-3412790","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3412790","identity":"rs-3412790","version":["v2"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}