CHARACTERISTICS OF FIXATIONS IN HUMAN INFANTS (EYE MOVEMENTS, MARKOV).
Item
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Title
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CHARACTERISTICS OF FIXATIONS IN HUMAN INFANTS (EYE MOVEMENTS, MARKOV).
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Identifier
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AAI8629699
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identifier
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8629699
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Creator
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HARRIS, CHRISTOPHER MARK.
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Contributor
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Louise Hainline & Israel Abramov
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Date
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1986
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Developmental
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Abstract
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When we freely view a scene, our eyes move in a sequence of saccades and fixations. Only during fixations, when the eyes are relatively stationary, is most (if not all) visual information acquired. Consequently, it is widely believed that fixations represent processing time and are driven by perceptual and/or cognitive processes. This view is disputed here, and instead, it is argued that visual scanning is basically a reflexive behavior.;Eye movements were recorded from 200 infants and 11 adults using a TV-based infrared corneal eye tracker. All records were manually parsed to isolate fixations and saccades.;It is shown that fixation duration is distributed exponentially for all subjects. The exponential is a basic waiting-time distribution and it is deduced that fixations are terminated by saccades triggered randomly in time by a memoryless mechanism. It is also found that the likelihood of a saccade increases with stimulus size. Thus, fixation termination is influenced by stimulating the peripheral retina rather than the fovea.;A "multiple target model" is proposed in which saccades are triggered by targets in the entire visual field with constant probability per unit time. This exogenous process is Markovian and a theoretical treatment makes quantitative predictions which are corroborated by other studies.;It is then shown that the likelihood of a saccade increases with the rate of drift of the eye during a fixation. This is because of the increased saliency of visual targets when they drift across the retina. The occurrence of saccades also increases as arousal level of infants increases, as measured by the speed of saccades. The effect of state is incorporated into the model.;It is concluded that, while free-viewing, fixation duration is determined by the occurrence of saccades which are triggered by the stimulus at the level of the retina--not at higher levels of the brain.;Although this reflexive model is a radical departure from the current cognitive view, it is conceptually simple and testable. It makes a strong distinction between looking (directing gaze) and seeing (acquiring information). The ramifications of this distinction are discussed with respect to methodologies used to assess the infant visual system.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Psychology
