The Relationship between Area and Threshold in the Central Fovea for Lights of Different Colours

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Abstract
The relationship between the size of a field and its threshold intensity was studied for small fields in the central fovea. Within the limits investigated, no significant difference was found whether this relationship was detd. for red or violet light. While it is possible that there may be a continuous relationship between threshold intensity and size of field, a rather sharp change was actually found in the relationship when the field subtended an angle of about 5[image] or 6[image]. Between this size and a field subtending about 20[image], the expression [image]A I = C described the findings, but with smaller fields the relationship A I = C was more nearly, though not absolutely, true. Exptl. difficulties may limit the extent to which the observations can be described by the second equation.