KodaliVilkhuJolly

Introduction

The human eye is always moving: usually either large movements to smoothly track a target in a scene or small ballistic movements that occur even when fixated at a single point in a scene. While the exact purpose of the small, continuous (fixational) eye movements is still an area of active research, literature agrees that the primary purpose is to counter perceptual image fading [1]. Perceptual fading occurs when a static image is projected onto the retina and higher-level, cognitive function results in a perceived fading of the image over time due to the lack of change of stimulus (see Appendix A for an optimal illusion demonstrating this effect). Therefore, the purpose of fixational eye movements is to provide a mechanical "refresh" of the visual system to have continual neural responses even to static scenes.

Specifically, for the scope of the Psych 221 final project, we set out to explore how fixational eye movements contribute to human visual acuity. This is a tangible problem that allows us to leverage the ISETBio toolkit [2] and our understanding of how to interpret Modulation Transfer Function (MTF) curves.

Background

The primary inspiration of the study was from a paper out of Michele Rucci's lab, which illustrated the importance of fixational eye movements such as drift and saccades to accurately model the primate (macaque) visual system [3]. The study focused on determining the contrast sensitivity as a function of the retinal ganglion cell (RGC) output of macaque retina. This output was measured both with and without fixational eye movements (which was included as a parameter in a modeled retinal neuron), and the key finding was that the presence of eye movements was critical to replicating the observed contrast behavior demonstrated by past behavioral experiments (De Valois et al. 1974). This is illustrated in the figure below (from the paper), which clearly shows that the model with drift better matches the findings of behavioral experiments and actually leads to higher observed contrast sensitivity.

Based on the findings of this study, we were able to formulate a hypothesis that the presence of fixational eye movements improves human contrast sensitivity. This is the claim we plan to validate/contradict based upon simulating eye movements in the ISETBio toolkit.

Methods

- Techniques you used to measure and analyze

- Experimental procedures in enough detail so that someone could repeat your analysis

- Tools used

- What was the idea of the algorithms and data analysis?

Results

- Relevant graphs and/or images.

- Make sure you draw the reader's attention to the key element of figures

-Clear figure captions.

Conclusions

- Describe what you learned.

- What worked? What didn't? Why?

- What should someone next year try?

Appendix I

- Source code

- Extra test images, etc, and give a description of each link.

Appendix II

- Work breakdown between members