time, but we do not notice this saccadic overshoot. If we look at ourselves in the mirror to detect these movements, we will not see any movements, overshoots, misting. But looking at other people performing the same actions, we will see how their eyes move. The cause of the saccadic “breakthrough” (empty field) are masking effects.
With long-term observation of the stimulus, not only the inertia of vision can manifest itself, but also adaptation or temporary “fatigue” of the stimulated portion of the retina will occur. These effects can be demonstrated by a slope aftereffect based on the experience of J. Gibson (Figure 1.2.13) [Shiffman, 2008], [Abbasov, 2019]. To do this, close the vertical grating (Figure 1.2.13, right), for 40-60 seconds, fix the view on the point between the inclined gratings (Figure 1.2.13, left). Then open the right side and quickly translate the view on the point between the two vertical bars (Figure 1.2.13, right). For some time you will find that the vertical lines are inclined in the direction opposite to the direction of inclination of the grating lines in Figure 1.2.13, on the left. The post-slope effect is manifested in the short-term distortion of the perception of the apparent orientation of the visual stimuli that arise due to adaptation to the previous stimulus, oriented differently.
You can also demonstrate the effect of curvature aftereffect. It manifests itself in a violation of the perception of the obvious form of the stimulus due to the prolonged effect of the previous stimulus of a different shape or curvature. This phenomenon is illustrated by the experience presented in Figure 1.2.14. Similarly, for 40-60 seconds, fix your gaze on the point between the two curves (Figure 1.2.14, on the left), then transfer the glance to the fixation point between the straight lines (Figure 1.2.14, on the right). Vertical lines will seem curved in the opposite direction to the curve of the curves.
Figure 1.2.13 Tilt action.
Figure 1.2.14 Curvature after-effect.
1.2.5 Perception of Contour and Contrast
In a consideration of the current works in the field of contrast perception it is necessary to acknowledge the sufficiently detailed survey of [Ghosh, Bhaumik, 2010] in which the historical and philosophical aspects of brightness perception are analyzed. Although these questions have been studied for 200 years the mechanism of influence of some optical illusions has not been determined to a full degree. The neuronal mechanism of perception formation from the visual receptors to brain cortex is described on the basis of bottom-up processes (Figure 1.2.15). The internal test squares with the same brightness form a contrast to the gradient ground (Figure 1.2.15, from the left). Moreover, the contrast effect is remained on the ground of sole-colored vertical stripes (Figure 1.2.15, from the right).
The perception of brightness is offered to be analyzed according to two philosophical tendencies: idealistic and materialistic approaches. The theory of contrast is based on the lateral inhibition similar to the principal dialectic laws: contradictions unity, interrelation, transition from quantity to quality, negation of the negation. Some recent researches of the experimental psychophysics and application of mathematical methods of modeling are based on that. To ensure the adequacy of such models it’s necessary to apply the quantitative representation of complex psychical processes on the basis of dialectic law of interaction between the part and the whole.
In the process of perception of visual information contours play a significant role. Using contours, we recognize the shapes, edges, and borders of surrounding objects. To study the neural mechanisms of perception of the contours, you can use the visual system of the horseshoe crab. The eye of the horseshoe crab is structurally complex and consists of about 1,000 receptors (ommatidia). Each receptor has its own neuron and optic nerve, which responds to the light signal independently of the adjacent receptors. They are not related to each other; stimulation of one receptor is not transmitted to the next. However, at a higher neuronal level, adjacent receptors are connected by lateral nerve fibers, while simultaneous stimulation of neighboring receptors results in the summation of their activity.
Figure 1.2.15 Brightness assimilation [Ghosh, Bhaumik, 2010].
Illumination of one receptor reduces the sensitivity of its neighboring receptors, and lateral inhibition occurs. When simultaneously illuminated, each receptor responds less actively than in the case of individual stimulation. Similarly, the ganglion cells of the human retina function in a human; they have complex interrelationships and are not individually excited. Neural connections using lateral braking affect the activity of each other, thereby ensuring a clear perception of edges and boundaries.
1.2.6 Mach Bands, Hermann’s Grid
To demonstrate the effect of lateral inhibition, consider the stepwise stretching of gray color in Figure 1.2.16. The left side of each vertical rectangular strip will appear a little lighter than its right side, which causes an increase in edge contrast. However, each strip has the same lightness; it is filled with a uniform gray color. This can be easily seen if we examine each rectangle alternately, covering the others. The effect of changing the lightness of the marginal sections is named after the 19th-century German physiologist Ernst Mach, who first described this phenomenon [Abbasov, 2016].
Spatial frequencies
Contrast areas of the surrounding field of view can be characterized by spatial frequency, i.e., the number of luminosity variations in a certain part of space. For experimental confirmation, consider Figure 1.2.17. The left upper lattice has a relatively low spatial frequency (wide bands), and the lower one has a higher frequency (narrow bands). The spatial frequencies (bandwidths) of the grids in Figure 1.2.17, on the right are identical and they occupy an intermediate position. Cover the grids in Figure 1.2.17, on the right and for at least 60 s, carefully examine the grids in Figure 1.2.17, on the right, fixing the view on the central horizontal strip between the gratings. After completion of the adaptation period, translate the view into the strip in the center between the two gratings in Figure
