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[Visual extinction: a study by means of potentials evoked with movement]
D Ramírez1, M Valdés-Sosa, K Torres
1Facultad de Medicina Julio Trigo López, Instituto Superior de Ciencias Médicas de La Habana, Cuba. viole@jtrigo.sld.cu
Introduction:
The term extinction refers to the phenomenon in which a patient with a lesion of the central nervous system ignores one of two stimuli in conditions of simultaneous bilateral stimuli. Various studies observe this phenomenon as the expression of a deficit in the process of selective attention, but there are few studies with potentials related to events (PRE).
Objectives:
To find the possible electrical correlation of the extinction phenomenon and the stage of processing at which this occurs.
Patients And Methods:
We studied a patient with a right parieto occipital lesion and a control person of the same race, age, sex and educational level. We carried out two experiments. The first of these was to determine the direction of movement of two surfaces with red and green spots situated on both sides of a central fixation point. In the second experiment, the same task was carried out, but the two surfaces were superimposed, in the same place. In both cases the first movement occurred in the surface which was being attended to and the second might be this surface or the other. The proportion of correct answers were recorded for both movements. The PRE showed an attention disorder which affected the spatial distribution of attention with conservation of the attention to objects.
Conclusions:
The suppression of the P1 N1 components are the electrical correlate of the phenomenon of extinction which should occur during early stages of processing. Further investigations are necessary in a larger number of cases.