Simulation of view. Part Four. Eye tracking

^{1 Excursion in the eye - 2 Perception - 3 Geometry of view - 4 Eye tracking - 5 How to catch the eye - 6 Simulation of eye tracking}

A post about the nature of what is actually being modeled, why this eye tracking is needed, etc. If some terms are not clear, then pay attention to the third post about the geometry of vision.

Attention and saccades

Saccades are manageable — they can be deliberately called (to translate the eyes), but reflex movements are also possible, due to the need to examine in more detail an object seen by peripheral vision. It is easy to notice: if something makes a sudden movement within the limits of peripheral visibility, then a reflex saccade will occur in order to examine in more detail what this movement was caused by.

It is easy to see that the duration of optical focusing of the eyes after a saccade on any region of the image is proportional to the attention paid to a detailed study of this region.
')
Even before the appearance of eye tracking technology, other, more time consuming ways of tracking tracks were proposed (a mirror on a contact lens and a hare thrown onto a photographic plate, as well as the magnetic resonance tracking method proposed by academic Yabrus). Here is an example of a trace from Yabrus’s monograph “The role of eye movement in the process of vision”:



The duration of each entry is 3 minutes. Each line fragment corresponds to a saccade.

1. Examining the picture without prior instructions.
2. Received the task to assess the financial situation of the family in the picture
3. Determine the age of the people depicted
4. Imagine what family members were doing before the arrival of an unexpected guest.
5. Remember how characters are dressed
6. Remember the location of people and objects in the room
7. Determine how long the unexpected guest has been away

Because of the ability to determine the degree of attention to certain regions of images, eye tracking technology receives so much attention from designers and psychologists of usability.

There is also a feedback between optical focus and attention : everything that appears in the field of view of the eye automatically begins to receive more attention. Thus, if, as a result of a reflex unconscious saccade, the optical focus has been established on some region (something “just attracts the eye”!), Then this region will be subjected to a better study and it will be better remembered.

There is also a certain interest in what place the end point of the saccade will be in, in the event of a conscious movement of the eyes to the interesting region.

Unconscious movements

Unconscious saccades occur according to four rules, each of which can play a role:

1. Accompanying movement.
   
   • The saccade is performed to prevent the movement of the tracked object. An example is the movement of the eyes of people looking out the window in a train.
   • Another possible cause, which provokes this type of saccades, is the image of a potential movement. Example: an image of an unstable construction is obtained. The glance will reflexively skip to the calculated point where, in theory, this construction should fall.
   • Due to the fact that in a flat image the gaze often tries to find movement, this type of saccade can also provoke the direction of gaze in a portrait of a person, the image of a flying arrow, etc.
2. Peripheral vision is seen psychologically active way. For example, when peripheral vision detects any hint of a person’s face, a saccade will be performed to test this image. In addition to the faces of people (for the recognition of which the whole isolated part of the brain is responsible!), The image of a Kalashnikov assault rifle, etc., can become psychologically active, for example, for the military. ;)
3. Peripheral vision was detected visually active image . For example - a large object on the background of small, or void on the background of a uniformly shaded field, or a bright color spot. Saccade is performed for more detailed consideration.
4. Peripheral vision was found structurally more complex object (composed of a larger number of clearly distinguishable contours, etc.) than that studied at the moment. Saccade is performed for more detailed consideration.

Unconscious movements of the first two types are difficult to model (well, except perhaps the possibility of face recognition or the presence of familiar text symbols), since their necessity depends on mental patterns of image processing.

On the other hand, the second two types of saccades are perfectly computed during computer modeling. The latter is all the more important because it is the last two rules that have a significant impact on the end point of both conscious and unconscious saccades.

Pupil and attention

Interestingly, there is also a positive correlation between the attention paid to the study of a region, the duration of fixation of the gaze on this region and the width of the pupil. Experiments have shown that in the event of an increase in intellectual efforts (for example, reading a very complex word or a sharp emotional reaction), the pupil tends to expand.

In the case of eye tracking, the program does not have the ability to track the expansion of the pupil caused by the psychological components of the reaction to the image, but the duration and degree of attention to certain regions that are difficult to perceive can suggest.

^{1 Excursion in the eye - 2 Perception - 3 Geometry of view - 4 Eye tracking - 5 How to catch the eye - 6 Simulation of eye tracking}