# Function of Fixational Eye Movements for Fine Depth Perception

> **NIH NIH F31** · BOSTON UNIVERSITY MEDICAL CAMPUS · 2020 · $45,452

## Abstract

Project Summary
Stereopsis, the process of extracting depth information from differences in the images on the two eyes, is one
of the most important sources of 3D information in humans. Much has been learned about how the visual
system identifies corresponding points in the two retinas and the neural mechanisms responsible for estimating
disparity. Virtually all previous studies have focused on spatial characteristics of the retinal images, paying
little attention to eye movements. Humans continually move their eyes, even when attempting to hold gaze on
a single point. Fixational eye movements (FEM), which include small saccades (microsaccades) and incessant
eye drifts, constantly move the image on the retinas. FEM are now known to contribute to the processing of
luminance signals by transforming space into temporal modulations on the retina, enhancing fine spatial
details. My own previous research has shown that monocular FEM contribute 0.15 logMAR to visual acuity,
approximately two lines on an eye chart. Yet very little is known about: (a) the characteristics of FEM in the two
eyes as humans make fine depth judgments; (b) whether FEM contribute to the processing of disparity signals;
and (c) how standard models of disparity-sensitive neurons are affected by the real input signals resulting from
FEM. Until recently, experimental investigation of these questions would not have been feasible because of the
technical challenges of precisely recording FEM in both eyes during natural viewing and of controlling retinal
stimulation. Our lab has now developed new systems for accurate eye-tracking and real-time gaze-contingent
control to overcome these challenges. The objective of this proposal is to investigate the impact of FEM on
stereopsis at the behavioral, perceptual, and computational levels. Our main hypothesis is that FEM contribute
to fine depth j by introducing disparity modulations that drive the neural mechanisms of stereopsis. To test this
hypothesis, we plan to address three aims. In Aim 1, using new tools to precisely measure FEM, we will
provide the first high-resolution characterization of behavior during fixation and fine depth judgments of targets
at different distances. While the precision of monocular fixation is now well established in 2D, the precision of
binocular fixation in depth remains unknown, even though this behavior determines the actual input to the
visual system. In Aim 2, we will experimentally examine whether disparity modulations introduced by FEM
affect stereopsis. Using a custom system for gaze-contingent display to control stimulation of both retinas, we
will assess fine depth perception in the presence and absence of FEM. Aim 3 will focus on the impact of FEM
on neural computations. We will examine how the temporal input signals to the retinas measured in Aims 1 and
2 interact with known characteristics of binocular neurons in stereopsis. Unlike standard models of stereopsis,
FEM keep both retinal images in moti...

## Key facts

- **NIH application ID:** 9994312
- **Project number:** 5F31EY029565-03
- **Recipient organization:** BOSTON UNIVERSITY MEDICAL CAMPUS
- **Principal Investigator:** Janis Intoy
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $45,452
- **Award type:** 5
- **Project period:** 2018-09-01 → 2021-08-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9994312

## Citation

> US National Institutes of Health, RePORTER application 9994312, Function of Fixational Eye Movements for Fine Depth Perception (5F31EY029565-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9994312. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*