The dark focus of accommodation for an individual observer correlates highly with the magnitude of night, empty field, and instrument myopia. These anomalous myopias are interpreted as resulting from the passive return of accommodation to an individually determined intermediate dark focus when the stimulus for accommodation is degraded or absent, or when the need for accommodation is eliminated.

The Ponzo perspective illusion, a special case of space perception, is influenced by contextual factors, texture, stereopsis, and familiarity in addition to perspective cues. The importance of familiarity is demonstrated by cultural differences obtained with photographs of natural settings which emphasize depth cues.

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