Eye movement during fixation [1]:
1.
2.
micro tremor:
• only a half minute of arc. Typical amplitude of 5-30 arcsec [6].
• high frequency (50-60 Hz) and the oscillations are independent in the two eyes. Frequency up to 200 Hz [6].
• Their frequency has been mentioned 90 Hz in [5] and spatial frequency of 15 secs rotation of the eye
slow drifts:
𝑎𝑟𝑐𝑚𝑖𝑛
60 𝑎𝑟𝑐𝑚𝑖𝑛
1 𝑑𝑒𝑔𝑟𝑒𝑒
•
about 6 arcmin (6
=
=
)
𝑐𝑦𝑐𝑙𝑒
3.
10 𝑐𝑦𝑐𝑙𝑒
10 𝑐𝑦𝑐𝑙𝑒
•
About 1.5 to 4 arcmin [6].
1
•
velocity of 1 arcmin/sec (≅ 𝐻𝑧 ≅ 0.167 𝐻𝑧). Median velocity of 4 arcmin/sec [6].
6
•
Velocity of 10-100 arcmin/sec [7]
fixation saccades (microsaccades)
•
rotate the eye back toward the target 3 times per second (≅ 300~350 𝑚𝑠𝑒𝑐)
•
according to [2], it should be more than 750 msec
•
the saccades of the two eyes are conjugate but can be slightly different in amplitude
•
People can be trained to control fixation solely with drifts but we make saccades to get the eye back on target as
[3]
quickly as possible.
•
•
Size of cones in fovea≅ 30 𝑎𝑟𝑐𝑠𝑒𝑐
Size of cones in fovea≥ 20 𝑎𝑟𝑐𝑠𝑒𝑐 [7]
[4]
Saccades range in size from about 2 to 12 arcmin on single meridian, occurring at intervals ranging from 0.2 to 10
seconds. Saccades occur simultaneously in both eyes and are always binocular [6].
Histograms of the distributions of saccadic sizes show a sharp cut-off around 12 arcmin with a few outliers around
20 arcmin [6].
Investigators until about 1980 have generally respected a maximum size of 10–12 arcmin as the upper limit for
microsaccades [6]. It is certainly completely out of context, and distorts the nature of the debate, to call (as some
recent publications do) saccades of 0.5, 1.0, or even 2.0 deg, “microsaccades” [6].
[1] Oculomotor Functions & Neurology (http://schorlab.berkeley.edu/passpro/oculomotor/default.html)
[2] Benefits of retinal image motion at the limits of spatial vision
[3] https://www.quora.com/What-is-the-latest-research-on-the-purpose-of-microsaccades
[4] The Performance Evaluation of a Novel Methodology of Fixational Eye Movements Detection
[5] Visual Acuity and the Normal Tremor of the Eyes
[6] The significance of microsaccades for vision and oculomotor control
[7] On the possible roles of microsaccades and drifts in visual perception