Measures current central nervous activation (arousal).
The flicker-fusion frequency is regarded, with other criteria (e.g. EEG, SCR), as an indicator of the functional readiness of the central nervous system. The test is frequently used in clinical and pharmacological research. A number of studies have been conducted in the field of clinical neuropsychology, e.g. to measure drug-induced sedation.

The flicker frequency is measured using an increasing measurement technique. This means that the frequency of the flickering light is increased until a steady light is perceived. The fusion frequency is measured using a decreasing technique. This means that the frequency of a high-frequency light that the respondent perceives as a steady light is reduced until it subjectively starts to flicker. The respondent presses a button at the point at which this change in perception occurs.

S1: Determines flicker and fusion frequency (increasing and decreasing measuring mode)
S2: Determines only fusion frequency (increasing measuring mode)
S3: Determines only flicker frequency (decreasing measuring mode)

The following main variables are scored:

Fusion frequency (in Hz) and flicker frequency (in Hz) provide a measure of the activation level. The subsidiary variables provide information on reaction accuracy.