Researchers from Weill Cornell Medicine and the University of Rochester have discovered evidence that ocular drifts within the eye are controlled and directed by cognitive processes.
Give me some background first.
Ocular drifts are tiny, subtle, and seemingly random types of movements that our eyes make when fixed on something.
They shift a visual target on the retina by distances on the order of a fraction of a millimeter or so across a few dozen photoreceptors (cones), and are believed to improve detection of small visual details simply by scanning and converting spatial details into trains of visual signals over time.
Until now, previous research had indicated ocular drifts to be controlled cognitively only in a broad sense.
Now talk about this research.
Researchers were looking to test the role of fixational eye movement (FEM) generation by conducting a letter discrimination task with six healthy participants (4 females; ages 22-31) using sensitive equipment at the University of Rochester.
Each participant was asked to identify which of a pair of letters (H vs N or E vs F) was being shown to them while on a background of random visual noise.
Letter pairs were revealed at the center of gaze (1.5 deg in size), superimposed on a 1/f noise mask.
What else?
The experiment was designed to reveal open-loop effects—where the brain remembers and focuses on incomplete tasks more than completed tasks—such as cognitive control driven by specific prior knowledge of a task.
Additionally, open-loop influences were isolated by pure noise fields (with no letters) while subjects focused on determining specific letter pairs.
What did they expect to find?
Through computational modeling, the research team expected that optimal eye movements for discriminating between letters would cross the key elements distinguishing the letters at right angles.
Subsequently, they were able to hypothesize that there would be a more precise cognitive control directing ocular drift in both the lower left to upper right directions for the H vs N discrimination, while the E vs F discrimination would have more strictly vertical movements.
Actually findings?
Their hypothesis was accurate, even in subjects who were shown only noise after they expected to be shown a letter (accounting for 20% of the trials).
This indicated that ocular drift’s cognitive control may be a direct result of having specific prior knowledge of the visual task—regardless and independently of any incoming visual information.
Take home.
According to the study authors, this research underscores the interrelationship between the sensory and motor portions of vision and implies a non-conscious connection between the two.
Significance?
Such research like this, study authors stated, could potentially lead to further insight into the neuroscience of vision and, potentially, vision disorders—which have largely been viewed as retina disorders or sensory processing within the brain.
Expert input?
Jonathan Victor, MD, the study’s senior author, stated that, “What our findings suggest is that visual disorders may sometimes have a motor component too, since optimal vision depends on the brain’s ability to execute these very tiny movements.”