Saccades at their best

Suppose you are on a road trip, driving down the seaside. You see a gorgeous view of mountains, sea, and clear blue sky. Your eyes rapidly scan the coastal scenery, making short fixations on the objects before you and jumping back and forth all over the view. Your brain constructs an internal representation of what you see, tying it into a wholesome picture and anchoring each eye movement to a long-lasting memory. These short, darting eye movements are called saccades.  

Scientists from the University of Latvia study these rapid eye movements in meticulous detail. One of their recent work looked into how saccade eye movements are affected by stimulus position and contrast. In simple words, they wanted to know if saccadic eye movements change depending on where the thing you are looking at is and how noticeable something is compared to its surroundings. The study participants were presented with visual targets (a dot on a screen) with varying levels of contrast and at different positions on the screen. The study was designed using
Tobii Pro Lab software, and the eye movements were recorded with the
Tobii Pro Fusion eye tracker. 

The scientists looked into the following saccadic performance measurements: 

• Latency – how fast eyes start moving when they spot something.  
• Peak velocity – how fast eyes move when jumping from one point to another.  
• Accuracy – how precisely eyes land on an object that one is looking at. If a saccade lands precisely what one aims for, that would be considered a good saccade accuracy.  

The study results showed that the stimulus’s spatial positioning significantly affected saccade accuracy and latency. The best saccadic eye movement performance was observed when saccades were oriented to the left or right in a horizontal plane. When the stimulus was on a medium grey or black background, saccades to the right and left from the central point yielded the best performance. A low-contrast stimulus on a light grey background resulted in the worst performance.   

The study results suggest that saccadic eye movements are the quickest and most accurate when viewing objects in a horizontal plane and high contrast. Those studying saccades in the vertical plane might want to bear in mind that the saccade performance might not be comparable to those studied on a horizontal plane. Also, the background color matters – using different contrast stimuli on a medium grey or black background might help get the best saccade performance, while very low-contrast stimuli might worsen accuracy and speed measurements. 

Cited publication

Goliskina, V.; Ceple, I.; Kassaliete, E.; Serpa, E.; Truksa, R.; Svede, A.; Krauze, L.; Fomins, S.; Ikaunieks, G.; Krumina, G. The Effect of Stimulus Contrast and Spatial Position on Saccadic Eye Movement Parameters. Vision 2023, 7, 68.