CORRELATI ELETTROFISIOLOGICI DELLA PERCEZIONE DEL CONTRASTO

[Autom. eng. transl.] Introduction: The perception of contrast is one of the primary aspects of visual perception and, in humans, it has usually been studied with a psychophysical approach. In the present work we recorded the electroencephalographic activity in healthy subjects during a detection and discrimination task in which a gabor stimulus was presented at different levels of contrast. Method: 6 subjects participated in this study. The stimulus presented varied, with exponential increase, between 6 different contrast levels, the lowest of which corresponded to the psychophysical threshold level, calculated individually for each subject. The analyzes focused both on behavioral responses (accuracy and reaction times), and on electrophysiological indices evoked by the stimulus, such as related event potentials (P100, N2pc) and cerebral oscillatory activity. Results: The results showed that both the behavioral indices and the electrophysiological indices increased following a non-linear trend with respect to the contrast modulation, which increased exponentially between the different experimental conditions. While the magnitude of the early P100 visual component was modulated based on the physical characteristics of the stimulus, the later N2pc component varied with a course similar to the subject's performance, appearing to be predictive of behavior. Frequency analysis also showed an increase in power, in relation to the contrast variation, in specific frequency bands such as theta (4-7Hz) and alpha (8-14Hz), while no high frequency modulation was observed . Conclusions: The data of this study show how the cortical activity recorded by the visual areas can be considered more linked to the perceptive aspects of the subject rather than to the physical characteristics of the stimulus.