October 2020
Volume 20, Issue 11
Open Access
Vision Sciences Society Annual Meeting Abstract  |   October 2020
Microsaccades around the visual field
Author Affiliations & Notes
  • Simran Purokayastha
    New York University
  • Mariel Roberts
    New York University
  • Marisa Carrasco
    New York University
  • Footnotes
    Acknowledgements  NIH NEI R01-EY027401
Journal of Vision October 2020, Vol.20, 1524. doi:https://doi.org/10.1167/jov.20.11.1524
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      Simran Purokayastha, Mariel Roberts, Marisa Carrasco; Microsaccades around the visual field. Journal of Vision 2020;20(11):1524. doi: https://doi.org/10.1167/jov.20.11.1524.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

[Goal] Visual performance fields (PFs) are characterized by two asymmetries: Performance is better along the horizontal than vertical meridian (Horizontal-Vertical Anisotropy) and along the lower than upper vertical meridian (Vertical Meridian (VM) Asymmetry). Here, we investigated how the directionality of microsaccades (MS, fixational eye movements <1°) vary during a visual discrimination task with stimuli placed along the cardinal meridia, for which discriminability varies (Experiment 1) or is equated across all locations (Experiment 2). [Methods] Observers performed a 2AFC orientation-discrimination task, which depends on contrast sensitivity, while maintaining fixation. On every trial, 4 Gabors briefly appeared simultaneously at 4 cardinal, isoeccentric (6.4°) locations. Shortly thereafter, a response cue indicated the target. In Experiment 1, contrast was fixed across locations. In Experiment 2, we equated task performance across all locations using different contrast thresholds per location. Eye fixation was monitored with an eye-tracker. Microsaccades were detected with a standard velocity-based detection algorithm (Engbert & Kliegl, 2003). [Results] We found typical PFs in the discrimination task for Experiment 1, and same discrimination across locations (by design) in Experiment 2. However, MS patterns were similar in both experiments. From trial- to response- cue onset, MS were more frequent toward the horizontal and upper-vertical locations than the lower-vertical location. But immediately after response cue onset, observers made more MS toward the target meridia; i.e. horizontal (vertical) bias when targets were on the horizontal (vertical) meridian, and more MS toward the upper- than lower- VM. [Conclusions] MS-direction follow the same pattern regardless of whether discriminability differs or is similar across isoeccentric locations. Interestingly, when stimuli are placed along the cardinal meridia, there is no overall MS horizontal bias. Once observers know the target location, MS are biased along the corresponding meridia, and in particular to the location where discriminability is typically lowest (upper-VM).

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