Electroretinograms evoked in man by local uniform or patterned stimulation

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Abstract
Electroretinograms (erg) were recorded in normal subjects. Television monitors were used as stimulators. The screens were surrounded by brightly lit white reflecting surfaces to ensure that the responses were developed by defined retinal areas. Various types of stimuli were employed. Either a pattern of dark and bright squares was reversed to evoke a pattern erg (perg), the luminance of the uniform screen was abruptly increased and decreased to evoke a focal on-off erg, or a pattern was made to appear and disappear from a uniform background. In each case, the sequence of changes of luminance at any one point could be made identical. Whether the erg was modified by the spatial organization of the stimulus was determined. A color monitor was used so that a red-green flicker, red-green pattern reversal or the appearance of a red-green pattern from a yellow background could be used as a stimulus. The responses were caused by the changes in hue, since all the colors were equiluminant. With black and white patterns the perg peaks 5 ms later than the focal on-off erg. The largest response is produced by squares of 0.5-1.degree. subtense. The ratio of the amplitudes of the perg to the focal on-off response is largest for stimuli confined to the macula and smallest for those projected onto peripheral retina. The amplitude of responses to chequerboard reversing patterns increases nearly linearly with contrast up to the maximum contrast available. The responses to change of hue are 70% as large as those produced by black and white patterns. The same ratio occurs for pattern and focal on-off erg. When colored patterns appear from and disappear to a uniform field, the erg evoked are very similar to those recorded when the appropriate changes of hue occur in a uniform field. This result is quite different to the findings for black and white patterns. Apparently, it is the change in local adaptation caused by the black and white patterns which modified the erg and not the presence of contrasting borders.