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Mark Nawrot, Lindsey Joyce; Hering's law tested with the pursuit theory of motion parallax. Journal of Vision 2008;8(6):661. doi: 10.1167/8.6.661.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system requires a pursuit signal to disambiguate the depth-sign of motion parallax (MP). The pursuit theory of MP suggests that stimulus motion in the same direction as pursuit is perceived in near depth. Absent the pursuit signal, depth from MP is ambiguous. This perceptual role for pursuit, separate from moving the eyes, may help us better understand the pursuit system. Hering's Law of Equal Innervation states that the drive signals to the two eyes are a linear combination of a vergence (disconjugate signals to the two eyes) and version (conjugate pursuit signals to the two eyes). One recent alternative is that the eyes receive individual drive signals. These experiments used random-dot MP stimuli on which observers performed depth-phase judgments. Binocular viewing was accomplished with ferro-electric shutter glasses. The MP stimulus was presented to a single eye while a fusible framework and fixation point was presented stereoscopically. Fixation point movement directly towards one eye results in asymmetric eye movements. Hering's Law suggests the moving eye is driven in the same direction by both vergence and version signals, but the stationary eye receives equal and opposite vergence and version signals. An MP stimulus presented to the stationary eye is unambiguous with the depth sign concordant with the direction of the pursuit signal given by Hering's Law. In control conditions, with the previously moving eye now occluded, the MP stimuli are ambiguous. Vergence does not appear to disambiguate MP. In addition to supporting Hering's Law and the pursuit theory of MP, these results indicate that a pursuit signal can be generated, and can disambiguate depth from MP, with the eye remaining stationary. This provides additional support for previous results suggesting pursuit can countermand full-field OKR and disambiguate depth from MP, even though the eye remains stationary.
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