Afterimage - zanzou (English spelling) afterimage English

When you gaze at a light and then look at a wall, an image of the light appears on the wall. This is called an afterimage. In this way, excitement remains even after the stimulus is removed, creating a sensation that is either the same as the original stimulus (positive afterimage) or different (negative afterimage). The apparent size of this afterimage is proportional to the distance to the projection surface, a phenomenon known as Emmert's law. Also, when you look at a moving object and then look at a still object, it appears to move in the opposite direction to what you saw before; this phenomenon is called a motion afterimage. For example, if you look at a flowing waterfall for a while and then move your gaze to a nearby still surface, that surface appears to move in the opposite direction to the flow of the waterfall, which is an example of a motion afterimage.

Afterimages appear in various brightness, shape, size, and other transformations. The original stimulus of a complex shape is transformed into an afterimage of a simple shape, and if there is another shape on the projection surface, the afterimage is drawn to it. Afterimages last only for a short time after the stimulus is removed, but intuitive images can appear even after several days.

[Shogo Imai]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

電灯を注視してから壁を見ると、壁の上に電灯の像が現れる。これを残像という。このように、刺激が除去されたあとも興奮が残り、元の刺激と同質（陽性残像）あるいは異質（陰性残像）の感覚が生じる。この残像の見かけの大きさは、投影面までの距離に比例し、これをエンメルトの法則Emmert's lawという。また、動くものを見たあとで静止したものを見ると、前に見たものと反対の方向に動くように見えるが、この現象を運動残像という。たとえば、滝の流れをしばらく見たあとで視線を周囲の静止面に移すと、その面が滝の流れと反対方向へ移動して見える現象は、運動残像の例である。

　残像は、いろいろな明るさ、形、大きさなどの変容の像(かたち)で現れる。複雑な形の元の刺激は単純な形の残像に変容し、投影面に他の図形があると、残像はそのほうへ引き寄せられる。また、刺激の除去後、残像は短時間だけ持続するが、直観像は数日後でも現れることがある。

［今井省吾］

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