Eye-movement Language

Each language construct can be composed of different basic eye-movements.

Basic eye-movements are saccade, fixation, smooth pursuit, and nystagmus. 

(i) Fixations: - “eye movement which stabilizes the retina over a stationary object of interest” [6]. Eye-fixations are accompanied by drift, small involuntary saccades and tremor. A human’s eye perceives the highest quality picture during an eye-fixation. Eye-fixations represent the areas of perceptual attention focus. Fixation duration usually ranges from 150 msec. to 600 msec.

(ii) Saccades: - “rapid eye movements used in repositioning the fovea to a new location in the visual environment” [6]. Saccade duration ranges from 10 msec. to 100 msec., which renders the visual system blind during a saccade [30]. If a stimulus that might attract a saccade appears in peripheral vision, there is a 100-300 ms. delay before the saccade occurs. There is a 100-200 ms. minimum refractory period after one saccade before another one can be made [2].

(iii) Smooth pursuit:  - eye movement that develop when the eyes are tracking a moving visual target. It occurs only to response to the moving object. This motion does not occur when the user is viewing a static scene. Smooth pursuit consists of these two components: a slowly varying motion component plus a saccadic component. This saccadic component occurs occasionally as a correction mechanism for the eye-position when the current eye-position is not accurate with respect to the moving object [31]. The slowly varying motion component keeps the retina stable over the moving object and high quality visual data is perceived during this period.

(iv) Nystagmus: - “are conjugate eye-movements characterized by a sawtooth-like time course (time series signal) pattern. Optokinetic nystagmus is a smooth pursuit movement interspersed with saccades invoked to compensate for the retinal movement of the target. Vestibular nystagmus is a type of eye movement compensating for the movement of the head” [6]. This pattern of eye movements occurs when viewing a fast moving repetitive scene – the train window phenomenon.

The scenario when a user is sitting in front of a computer would be similar to the case of viewing a static scene. Thus, primarily two types of eye-movements will occur: saccades and fixations. If a moving object is introduced on the computer screen then the smooth pursuit might develop.

Basic eye-movements table:

The described eye movements can be detected by the Attention Focus Kalman Filter.

Eye-movement language constructs are created through the combination of each basic eye-movement type. The spatial and temporal information have to be incorporated in the design of each eye language token.

Additional challenge in eye language token creation comes from the notion that some of the eye-movements can be controlled while the others cannot. As an example an eye-fixation is voluntary eye movement, each of us can look at a point of interest and examine it at will. In case of saccades some of them are voluntary and the others are not. If we move our eyes from one point of the screen to another point, the saccadic eye movements involved would be voluntary. In case if we are looking at the screen and something catches our attention at the periphery of our vision we move our eyes using involuntary saccades. Smooth pursuit eye-movements are completely involuntary and the match the speed of a moving object under certain speed conditions.