Spatial contrast sensitivity and visual accommodation studied with VEP (Visual Evoked Potential), PET (Positron Emission Tomography) and psychophysical techniques
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- Franzén O., Lennerstrand G., Pardo J., Richter H. (2000) Spatial contrast sensitivity and visual accommodation studied with VEP (Visual Evoked Potential), PET (Positron Emission Tomography) and psychophysical techniques. In: Franzén O., Richter H., Stark L. (eds) Accommodation and Vergence Mechanisms in the Visual System. Birkhäuser, Basel
Psychophysical scales of a 3,3 c/deg monochromatic checkerboard of variable contrast were compared with steady state visually evoked potentials (VEP) recorded by gross electrodes on the scalp. These estimates of neuronal population responses grew as a power function of physical contrast having an exponent of approximately the same magnitude as the corresponding psychophysical function which gives credence to the validity of the procedures employed. The functional neuroimaging technique of positron emission tomography (PET), based on radioactive decay of a labelled tracer occurring inside the brain, was applied in normal subjects to quantitatively explore the influence of voluntary positive accommodation and also to examine the effect of reduced contrast sensitivity in human strabismic amblyopia. A great asymmetry in metabolic activity was observed in the striate cortex, that is, the Brodmann area 17 (BA 17) activation was strongest contralateral to the dominant viewing eye. The PET scans revealed, however, a high correlation between blood flow increases in the right striate cortex (BA 17) and the left extrastriate cortex (BA 18) during voluntary accommodation, possibly reflecting top-down modulation and reentrant processes. The poor contrast sensitivity in strabismic amblyopia could essentially be explained by deactivation of the ipsilateral extrastriate cortical areas BA 18 and BA 19.
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