City Research Online

Abstract

Since Ibn al-Haytham (c.1021), one of the central questions of vision science has been how the visual system extracts absolute distance information from the environment in order to scale the size and distance of objects in the scene. Since Kepler (1604) and Descartes (1637), emphasis has been placed on a number of distinct ‘triangulation’ cues: vergence (the angular rotation of the eyes), accommodation (the focal power of the eyes), motion parallax (the change of the scene with motion), and, more recently, vertical disparities (the differences in the vertical projection of points in the two eyes). However, there is increasing skepticism about accommodation and motion parallax, and I argue that when vertical disparities have been properly tested, they too prove ineffective. Which only leaves vergence. However, in three experiments I demonstrate that vergence is not an effective absolute distance cue. Which leads us to the following conclusion: If all of the remaining potential absolute distance cues are either cognitive in nature (familiar size) or limited in context (ground plane), we should instead be open to the idea that the visual system operates without absolute distance information, and scale is not conveyed by our visual experience.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	Doctoral Theses School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses School of Health & Psychological Sciences > Optometry & Visual Sciences

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