Experimental tests of hypotheses for microsaccade generation

Abstract

Fixational eye movements such as microsaccades are important to prevent fading. These miniature eye movements are also necessary to redirect gaze to the target after a drift. Generation of saccades and microsaccades utilizes common neural substrates. We, therefore, hypothesized that physiological modulators of saccades should also affect microsaccades. Test of this hypothesis will also provide support for the models of a microsaccade generation. We performed two experiments. In the first experiment, complete darkness led to a decrease in the frequency and velocity, but increased the amplitude of microsaccades. In the second experiment, active eyelid closure further reduced the velocity and frequency of microsaccades, but increased their amplitude. Darkness reduces the superior colliculus activity leading to a reduction in the velocity and frequency of microsaccades. Eye closure might cause sustained inhibition of the omnipause neurons. Subsequent disinhibition of the burst neurons might cause a reduction in the post-inhibitory rebound firing resulting in a decreased velocity of microsaccades. Sustained inhibition of the omnipause neurons could also reduce the inhibitory drive that would otherwise abort microsaccades. Hence, by inhibiting the activity of omnipause neurons, the eye closure could increase the amplitude of microsaccades.

Reduced fixation stability induced by peripheral viewing does not contribute to crowding

“…Therefore, the definition of microsaccades that we used for this study could potentially include both microsaccades and small-amplitude saccades. The eye movement data were converted to degrees and filtered using a Savitsky-Golay filter with an order of 3 and a frame length of 41 (Cherici, Kuang, Poletti, & Rucci, 2012;Ghasia & Shaikh, 2015;Ko, Snodderly, & Poletti, 2016). The filtered eye movement data were used for further analysis.…”

Visual Search in Amblyopia: Abnormal Fixational Eye Movements and Suboptimal Sampling Strategies

“…The visual cortex signals microsaccade production while the superior colliculus drives such input to generate microsaccades. [40][41][42] Therefore, visual cortical impairment likely affects the physiology of subcortically generated microsaccades. Studies have shown that during fixation, amblyopes have decreased microsaccade production.…”

Fixational eye movements in Tourette syndrome

“…We then normalized the proportion of microsaccades in a given bin to the size of the population. Such normalization allowed comparison of the distributions without being affected by uneven sample size [20]. Normalized occurrence of microsaccades is plotted on the y -axis while corresponding bin value is plotted on the x -axis.…”

“…In order to exclude visually guided or voluntary saccade, we used saccades that did not accompany target shifts and were smaller than 4° amplitude. The variables of interest were as follows: amplitudes, intersaccadic invervals, peak velocities, and drift velocities and variance in eye position during intersaccadic interval; data analysis was performed using custom-prepared software in Matlab ™ programming language [20]. Further analysis was performed in three steps.…”

“…In normal population, their amplitude increases in darkness [19, 20] and their rate increases during tasks requiring high acuity [21]. Task difficulty [22], mental fatigue [23], fixation target size [24], and informativeness of the natural scene [13] are known to affect microsaccades.…”