New Findings in Visual Perception and Eye Movement Research

Background Introduction

In daily life, despite the constant rapid eye movements (known as saccades), we are still able to perceive a stable visual environment. This stability is achieved through the integration of information by the visual system during saccades. However, the mechanisms of visual processing during saccades remain a complex and incompletely understood issue. In particular, when brief visual stimuli are presented during saccades, the perceived locations of these stimuli are often mislocalized, a phenomenon known as “perisaccadic mislocalization.” This phenomenon is believed to be related to the “corollary discharge” signals associated with saccade-related neural motor commands.

Recent studies have shown that motor bursts in the superior colliculus (SC)—a known source of corollary discharge—vary depending on the visual features of the saccade target. Based on this finding, this study aimed to investigate whether perisaccadic mislocalization is also influenced by the visual features of the saccade target. Specifically, the researchers hypothesized that if corollary discharge signals not only convey saccade vector information but may also transmit visual feature information of the saccade target, then the strength of perisaccadic mislocalization might vary depending on the visual features of the saccade target.

Research Source

This study was conducted by Matthias P. Baumann, Anna F. Denninger, and Ziad M. Hafed from the University of Tübingen in Germany. The research team is affiliated with the Werner Reichardt Centre for Integrative Neuroscience and the Hertie Institute for Clinical Brain Research at the University of Tübingen. The study was published on November 19, 2024, in the Journal of Neurophysiology.

Research Process and Results

Experimental Design

The research team designed a psychophysical experiment in which human participants were asked to report the location of a brief visual stimulus presented during saccades. In the experiment, participants were required to generate saccades toward the center of a Gabor grating with two different spatial frequencies (low spatial frequency: 0.5 cycles/°, high spatial frequency: 5 cycles/°). To ensure the accuracy and consistency of the saccades, a high-contrast target spot was always placed at the center of the grating.

During the saccade, the researchers presented a brief, high-contrast visual stimulus (referred to as a probe) at different time points and asked participants to click on the perceived location of the probe using a mouse cursor. The probe presentation times were categorized into three groups: approximately 30 milliseconds (t1), 70 milliseconds (t2), and 110 milliseconds (t3) after saccade onset. This approach allowed the researchers to measure the strength of perisaccadic mislocalization and compare the differences in mislocalization under different saccade target visual features.

Data Analysis

The research team conducted a detailed analysis of the participants’ saccade trajectories and click locations. First, they ensured that the saccade vectors and kinematic parameters (such as peak velocity) were matched across different saccade target conditions. Then, they calculated the Euclidean distance between the participants’ click locations and the actual probe locations as a quantitative measure of visual mislocalization.

Key Findings

1. Effect of Saccade Target Visual Features on Mislocalization Strength: The study found that the strength of perisaccadic mislocalization was significantly higher for low-spatial-frequency saccade targets compared to high-spatial-frequency targets. This difference was particularly evident at probe presentation times t1 and t2 (p < 0.05). This indicates that the visual features of the saccade target indeed influenced the strength of perisaccadic mislocalization.

2. Effect of Visual Field Location on Mislocalization Strength: The study also found that the strength of mislocalization was significantly higher when the probe was presented in the upper visual field compared to the lower visual field. This result aligns with the overrepresentation of the upper visual field in the SC, further supporting the potential role of the SC in perisaccadic mislocalization.

3. Consistency of Probe Visibility: To rule out the possibility that differences in probe visibility might have influenced the results, the research team conducted a control experiment to measure the visibility of the probe under different saccade target conditions. The results showed that although the detection threshold for the probe was slightly higher under low-spatial-frequency saccade targets during maximal saccadic suppression (t1a), the visibility of the probe was completely overlapping for both saccade target conditions at time t2. Therefore, the differences in perisaccadic mislocalization cannot be simply attributed to differences in probe visibility.

Conclusions and Significance

This study is the first to reveal that the strength of perisaccadic mislocalization depends not only on saccade vector information but also on the visual features of the saccade target. This finding suggests that corollary discharge signals may not only convey motor information about the saccade but may also transmit visual feature information about the saccade target. This provides a new perspective for understanding how the visual system integrates information during saccades and offers important insights for future neurophysiological research.

Research Highlights

1. Novel Research Perspective: This study is the first to link the visual features of the saccade target with perisaccadic mislocalization, revealing the potential multifunctionality of corollary discharge signals.
2. Rigorous Experimental Design: By matching saccade vectors and kinematic parameters, the research team ensured the reliability of the results and ruled out interference from differences in probe visibility through control experiments.
3. Ecological Significance: The findings suggest that the visual system may prioritize the processing of low-spatial-frequency information, which aligns with the spectral characteristics of natural scenes and has important ecological implications.

Future Directions

Future research could further explore the mechanisms by which the SC and its corollary discharge signals transmit visual information during saccades. Additionally, by combining neurophysiological techniques, researchers could more directly observe the activity patterns of SC neurons during saccades, thereby gaining deeper insights into how the visual system integrates information during saccades.

This study not only provides new insights into the fields of visual perception and oculomotor control but also offers a potential theoretical foundation for future clinical applications, such as the diagnosis and treatment of visual disorders.