Psychophysical dissociation of phase and position cues for visual motion perception

Thesis

Visual motion perception is essential for viewing and interacting with our environment. The motion of an object in the visual field can be described by the changes in the position of a feature over time (‘position cues’ in the spatial domain), or by changes in the phase of the spatial frequency components in the Fourier domain (‘phase cues’). This thesis investigates the relative extent to which people rely on these cues to infer movement in the visual scene.

I showed that apparent motion discrimination with phase cues and position cues can be psychophysically dissociated by temporal interval (Chapter 2), and spatial frequency (Chapter 3), and that displacement thresholds for position cues increase more rapidly with eccentricity than do phase cues (Chapter 3). When phase and position cues are conflicted, I demonstrated that these spatial frequency dissociations can predict reversals in reported motion direction, both with changing spatial frequency, and between foveal and peripheral viewing (Chapters 4 and 5). The reliance on position cues to infer motion correlates with the ability to discriminate shapes, such that when shape discrimination is impaired motion discrimination is reliant on phase cues, in both normal observers and in the scotoma of V1 lesioned patients (Chapter 6). This shows that the visual system treats phase and position cues as separate sources of information which could be analysed separately.

These psychophysical dissociations may reflect the properties of different detectors in the visual field. Correlations of models of cell density distributions with the displacement thresholds across eccentricity suggest that the pα and pβ retinal ganglion cells form the physiological substrates for the input to these phase and position systems respectively (Chapter 7).

This thesis presents a psychophysical dissociation between phase and position cues, and suggests that these cues are initially processed by separate systems, with distinct physiological substrates.

Authors: HIbble, A

• DOI: 10.5287/ora-erdqdnrz4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: motion illusions; retinal ganglion cell distributions; cortical blindness; reverse Phi; motion cues; psychophysics; blindsight; visual motion perception
• Subjects: Psychology; Visual pathways; Motion perception (Vision)