Effects of attention on pattern-reversal visual evoked potentials: foveal field stimulation versus peripheral field stimulation.

The effects of foveal field attention on pattern reversal visual evoked potential (VEP) were investigated in thirteen normal subjects. Conventional monocular VEP was recorded during the three conditions of control, foveal concentration and reaction time task. Three patterns of checker-board, which were full field (radius, 0-9 degrees), peripheral field (2.5-9 degrees) and foveal field (0-2.5 degrees), were presented for the stimulation in each condition. The P100 and N145 amplitude of the peripheral field VEP were significantly smaller during the concentration and the reaction time task conditions that that in the control session, while the foveal field VEP amplitudes were enhanced in the concentration and reaction time tasks conditions. The full field VEP amplitudes were not significantly changed by the conditions. We concluded that the act of concentration to the foveal field or the task requiring attention to the foveal field, enhanced the VEP response to foveal field stimulation and suppressed the VEP to the peripheral field. A gating effect in area V1 was speculated, although extra-striate cortex might contribute.