Saccades are rapid, simultaneous movements of both eyes in the same direction, allowing us to quickly shift our gaze. Occurring multiple times per second, these swift, jerk-like eye movements bring new objects into sharp focus, playing a foundational role in visual perception.
How Our Eyes Make Quick Jumps
When a saccade occurs, the eyes undergo a rapid, ballistic movement, meaning the trajectory is predetermined and cannot be adjusted mid-flight. These movements are incredibly fast, reaching up to 700 degrees per second. The brain initiates these swift shifts to direct the fovea, the retina’s area for sharp vision, onto a new target.
During a saccade, vision is temporarily suppressed, a phenomenon known as saccadic suppression. This prevents visual blur from the rapid eye movement, allowing us to perceive the world as stable. This suppression begins roughly 100 milliseconds before the eye movement starts, even for saccades lasting about 50 milliseconds.
The brain plays a role in initiating and controlling these movements, involving a network of regions. The frontal eye fields (FEF) in the frontal cortex plan and execute saccades. The superior colliculus, in the midbrain, processes visual information and initiates saccades, receiving inputs from the retina and other brain areas. These regions work together to ensure coordinated eye movements, with signals traveling to the brainstem and cranial nerves that innervate the eye muscles.
Saccades in Daily Activities
Saccades are integral to many everyday visual tasks, enabling efficient processing of our surroundings. When reading, our eyes do not glide smoothly; instead, they make a series of saccadic jumps, interspersed with brief pauses known as fixations. During fixations, the brain processes visual information before another saccade moves the eyes to the next word or text segment.
Beyond reading, saccades are fundamental to scanning a scene. Whether surveying a room, looking for a friend, or following a moving object, our eyes make quick, purposeful jumps. This allows us to rapidly gather information from different parts of our visual field.
Visual search tasks rely on saccadic eye movements. When searching for an item, saccades guide our gaze to potential targets, allowing quick examination of various locations. These rapid movements enable efficient search and location of objects, demonstrating their importance in selective visual attention.
When Eye Jumps Are Impaired
When saccadic eye movements do not function correctly, individuals may experience difficulties with visual tasks. Impaired saccades can manifest as slow, inaccurate, or absent movements. Eyes might jump randomly or move in uncoordinated patterns, making it challenging to maintain focus.
These impairments can stem from underlying causes, including neurological conditions. Diseases such as Parkinson’s disease, multiple sclerosis, and Alzheimer’s disease can affect saccadic performance, leading to issues like increased latency, decreased velocity, or reduced accuracy. Brain injuries, such as concussions, can also result in slower saccades, eye coordination problems, and difficulties with reflexive and voluntary eye movements.
The impact on daily life can be significant. Individuals may struggle with reading comprehension, skipping words or lines, or finding it hard to keep their place. Visual tracking of moving objects can become challenging, affecting activities like sports or driving. Difficulties with navigation and facial recognition can also arise, as these tasks rely on efficient and accurate gaze shifts. Such impairments often signal underlying medical conditions and warrant medical evaluation.