The Impact of Retinal Acceleration Error on Catch-Up Saccades

Research Background

When humans track moving objects, they primarily rely on two types of eye movements: smooth pursuit and saccades. Smooth pursuit depends on visual motion signals, but when tracking errors accumulate, the brain initiates catch-up saccades to realign the gaze with the target, ensuring the target remains on the fovea. Previous studies have shown that retinal position error and retinal velocity error are key factors in determining the latency and amplitude of catch-up saccades. However, whether retinal acceleration error also plays a role in this process remains unclear. In natural environments, objects often accelerate or decelerate due to gravity, friction, or external forces, making the study of acceleration error’s impact on saccades highly relevant.

This study aims to investigate whether retinal acceleration error influences the latency and amplitude of catch-up saccades and to validate its role in saccade triggering and amplitude computation. By designing an accelerating target tracking experiment, the research team hopes to reveal the specific contribution of acceleration error in saccade programming.

Research Source

The study was conducted by Sydney Doré, Jonathan Coutinho, and Gunnar Blohm from Queen’s University in Canada, Aarlenne Z. Khan from Université de Montréal in Canada, and Philippe Lefèvre from Université catholique de Louvain in Belgium. The research paper, titled “Latency and Amplitude of Catch-Up Saccades to Accelerating Targets,” was published on November 25, 2024, in the Journal of Neurophysiology.

Research Process

Experimental Design

The research team designed a double step-ramp task, generating experimental stimuli using MATLAB and the Psychophysics Toolbox. The experiment utilized a ViewPixx screen (120 Hz refresh rate) to present visual stimuli, and eye movements were recorded at 1000 Hz using the Eyelink 1000 system. The experiment included both accelerating and decelerating conditions, with the target randomly accelerating or decelerating horizontally. A randomly sized target step was introduced during the motion to trigger catch-up saccades.

Participants and Data Collection

The study recruited 15 adult participants, with 13 completing the experiment (8 females, 5 males, average age 21). Each participant underwent five data collection sessions, each lasting approximately 30 minutes, resulting in a total of 32,500 trials. During the experiment, participants tracked a white dot moving horizontally on the screen, with target acceleration randomly varying between -80 and 80 deg/s².

Data Processing and Analysis

Eye movement data were low-pass filtered (cutoff frequency 50 Hz), and eye velocity and acceleration were calculated using a central difference algorithm. Saccades were detected using an acceleration threshold of 750 deg/s². To remove the smooth pursuit component from saccades, the research team corrected saccade amplitude using the formula:
[ \text{corrected amplitude} = \text{saccade amplitude} - (\text{saccade duration} \times \text{pursuit velocity}) ]

Statistical Analysis

The study employed multiple linear regression to analyze the influence of retinal position error, velocity error, and acceleration error on saccade amplitude. The regression model was:
[ \text{corrected amplitude} = b{pe} \times \text{position error} + b{ve} \times \text{velocity error} + b_{ae} \times \text{acceleration error} ]
Additionally, repeated-measures ANOVA was used to assess the impact of acceleration error on saccade latency.

Key Findings

Saccade Amplitude

The study found that retinal position error, velocity error, and acceleration error all significantly predicted saccade amplitude (( b{pe} = 0.8373, p < 1.10^{-100} ); ( b{ve} = 0.0791, p < 1.10^{-100} ); ( b_{ae} = 0.0018, p = 2.029724e-09 )). Although the contribution of acceleration error was small, it was statistically significant. The study also found that after correcting saccade amplitude, actual saccades compensated for approximately 84% of position error, 46% of velocity error, and 16% of acceleration error.

Saccade Latency

The study showed that when retinal acceleration error aligned with the direction of predicted position error, saccade latency was shorter; conversely, it was longer. This result indicates that acceleration error indirectly modulates saccade triggering time by influencing the certainty of predicted position error. Specifically, when predicted position error was small, the effect of acceleration error on latency was more pronounced.

Research Conclusions

This study provides the first evidence of retinal acceleration error’s role in catch-up saccade programming. The findings reveal that acceleration error not only influences saccade amplitude but also modulates saccade latency by adjusting the certainty of predicted position error. This discovery expands our understanding of saccade triggering mechanisms and offers new theoretical support for future eye movement models.

Research Highlights

1. Innovative Experimental Design: By introducing an accelerating target tracking task, the study quantitatively assessed the impact of retinal acceleration error on saccades for the first time.
2. Multivariate Regression Analysis: The study employed a multiple linear regression model to reveal the independent contributions of position, velocity, and acceleration errors in saccade amplitude computation.
3. Theoretical Expansion: The research supports a Bayesian inference-based saccade triggering model, providing new perspectives for future neural computational models.

Research Significance

The scientific value of this study lies in uncovering the role of retinal acceleration error in saccade programming, filling a gap in the field. Additionally, the findings have potential applications in developing more accurate eye-tracking technologies and virtual reality systems. Future research could further explore the impact of acceleration error on eye movement behavior in natural scenes and its applications in daily tasks such as driving and sports.

Through this study, we have gained a deeper understanding of the complexity and adaptability of the human eye movement system. The discovery of retinal acceleration error not only enriches the theoretical framework of saccade programming but also opens new directions for future applied research.