Color vision and Frithiof Holmgren's discordant retinal microstimulation findings.

Frithiof Holmgren was a nineteenth-century Swedish professor of physiology who, after a sabbatical year at Helmholtz's laboratory in Heidelberg, devoted himself to studies of color vision and color blindness. Following Blix's successful demonstration of cutaneous receptor specificity by means of point stimulation, he decided to apply an analogous technique for psychophysical examination of the human retina. His findings appeared to support the Young-Helmholtz hypothesis of three primary colors and invalidated Hering's alternative four color opponent hypothesis. However, contemporaries (Hering, Isaachsen) could not reproduce Holmgren's results, and his findings fell into disrepute. They have now been confirmed, but their previous theoretical significance was not supported.