Tachistoscopy

Tachistoscopy (from ancient Greek τᾰχύς “fast” + σκοπέω “to observe”) is a method of recording fast processes using photography with a flash frequency exceeding the refresh rate of the image on the retina.

During tachistoscopy, an image of an object is photographed for 1/50-1/200 s (depending on the frequency of flashes and the characteristics of the visual apparatus of the subject), after which it is developed and recorded. The result is a series of photographs, each of which captures an image at the moment of a flash of light.

The tachistoscopic method allows you to study rapidly occurring processes (for example, electrical activity of the brain, muscle function, perception of light pulses, etc.) without distortions and interference that can occur with other recording methods. Tachistoscopes are used in various fields of science and technology, such as physics, chemistry, biology, medicine, etc.

Tachistoscopy is an optical-physiological method for studying the visual functions of the eye. The essence of the method is that at the moment the stimulus is presented, the electrical activity of the brain is recorded during a flash of light at a certain point in time. To study the temporal characteristics of nervous processes, the method of electrical stimulation with a current of varying strength and frequency is used. For this purpose, an electrical stimulator is used that generates an electric current. As a result, the amplitude of the action potential in the postural visual zone of the retina is close to one, and the frequency is close to another, coinciding with the frequency of the current. In this case, reactions to the stimulus are studied depending on the duration of exposure to the stimulus and its parameters and are compared with correlating time indicators of electrical activity of the cerebral cortex.

During the period of a light flash (duration measured in milliseconds), the biopotentials of only bipolar neurons are recorded, or bipolar cells are combined with rod or cone cells. Using a tachistoscope, it is possible to make a double measurement of the P1 wave potential of the cerebral cortex before the flash, the value of which serves as a reflection of the perception of brightness. Real-time changes in brightness provide information about the temporal response to light.