Vision span or perceptual span is a controversial concept referring to the angular span (vertically and horizontally), within which the

human eye The human eye is a sensory organ in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance. The eye can be considered as a living ...

has sharp enough

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

to perform an action accurately (reading or face recognition). The

visual field The visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; in ophthalmology and neurology the emphasis is mostly on the structure inside the visual field and it i ...

of the human eye spans approximately 120 degrees of arc. However, most of that arc is

peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...

. The human eye has much greater resolution in the

macula The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the retina of the human eye and in other animals. The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avas ...

, where there is a higher density of

cone cell Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most v ...

s. The macula has a diameter of about 16 degrees of the retina. The

field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...

that is observed with sufficient resolution to read text typically spans about 6 degrees of arc, which is wide enough to allow a clear view of about five words in a row when printed text at ordinary size is held about 50 centimeters from the eyes. Regarding face processing, the

with a sufficient amount of information in order to recognise faces accurately spans about 7° which represents about 45% of a face. The brain creates the illusion of having a greater visual span by automatically and unconsciously moving the center of vision into any area of interest in the field of view.

Application to speed reading

While reading, readers will fail to recognize a word unless they are fixating within three to four character spaces of the word. The same is true for speed readers and skimmers. Speed readers cannot answer questions about a main point or detail, if they did not fixate directly on it or within three character spaces of it. When a text is removed whilst reading, readers can only accurately report upon the word they were fixating upon or the next one to the right. There is no evidence from eye movement research that individuals are making predictions of text based upon hypotheses about the words in the periphery so that they can skip over or spend less time on unimportant or redundant words. Most speed reading courses claim that the peripheral vision can be used to read text. This has been suggested impossible because the text is blurred out through lack of visual resolution. At best the human brain can only ''guess'' at the content of text outside the macular region. There simply are not enough cone cells away from the center of the visual field to identify words in the periphery of the field. It has been suggested that the fixation span can be stretched through training ( meta guiding) to take in as much as a line for the purpose of skimming or speed reading. However other sources suggest that using this method can result in a severely reduced comprehension rate in comparison to normal reading (" rauding"). Some speed reading courses stress that the human eye has to move very quickly. They also stress that the human eye should move in a pattern to fill in the information that was not properly perceived. The effective limit for scanning speeds based upon the limit of the human eye's resolution is about 300 words per minute. It is claimed that such speeds also require great practice, and extremely rapid eye movements, although research suggests that such training is not possible. It has been suggested by some speed reading promoters that the readers who achieve such speeds are on the

autism spectrum Autism, also known as autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by differences or difficulties in social communication and interaction, a preference for predictability and routine, sensory processing d ...

. Research into reading rate suggests that study strategies, rather than speed reading, explains why expert readers, such as professors and editors, are more efficient than others.

Application to face processing

Face recognition system requires several fixation on different location (typically in a triangular pattern) for a face to be recognised. The same is true for the so-called Super Recognisers who are persons with high face recognition capabilities. Similarly to the reading span, the Facespan might be modulated by difficulty, expertise, age, disorder and other idiosyncratic differences between individuals. The idiosyncratic differences are thus most probably due to differences in Facespan rather than in oculomotor strategy. Previous study revealed that the Vision span is more accurately defined in number of characters rather than in visual angle.

Application to speed reading

Application to face processing

References

Further reading

See also