Spatial summation measured with visual evoked potentials

ABSTRACT

Spatial summation was measured in a healthy human subject, using as a criterion the threshold energy necessary to obtain steady state VEP. The results were then compared with those obtained using the subject's subjective sensory threshold. Measurements were made with an arrangement of a Fundus haploscope, oscilloscope and personal computer, using circular spot stimuli of various sizes, intensities, and positions. At the fovea, spatial summation was observed at central stimulus field sizes of smaller than 4.5 min in diameter with the VEP threshold and 3.5 min in diameter with the subjective threshold. When the stimulus site was moved 2 degrees peripherally, spatial summation was observed at stimulus field diameters of smaller than 8.4 min and 4.0 min with the VEP and subjective thresholds, respectively. These values roughly correspond with the Y cell receptive fields of the retinal ganglion cells.

Key words:

• spatial summation
• visual evoked potential
• threshold energy
• Y cell
• receptive field