Chapter 1 reports on an experiment measuring the extent of the bifixation space. Hering (1868) argued that the bifixation space is smaller for near viewing distances than for far. He also the templeward directed eye lagged behind the nasally directed eye with extreme gaze position. The data reported in this chapter support and expand on Hering's claim that the extent of the bifixation space is a function of viewing distance. We expand on this claim in this report by measuring the full area over which the eyes can move together. Our data conflict with Hering's second claim, however. We found that the templeward directed eye lags behind the nasally directed eye with extreme gaze position.
Chapter 2 reports on three experiments investigating the effects of occlusion on slant perception and visual direction. Hakkinen and Nyman (1997 Perception 26 29-38) have shown that perceived slant, associated with Ogle's (1938 Archives of Ophthalmology 20 604-623) geometric effect, is reduced when an occlusion scenario is a possible interpretation for the visual system. We present data from three experiments that confirm and expand on this finding. Our stimuli consisted of four types of stereograms depicting two white central rectangles each flanked by two gray rectangles. The central white rectangles varied in height, thus manipulating the polarity of the T-junction information. Perceived slant was smallest or not apparent when occlusion information indicated the central rectangles were nearer than the flanking rectangles and greatest when cues to occlusion were incompatible with a nearer central rectangle (experiment 1). Vertical visual direction estimates of the outer corners of the flanking rectangles were less accurate when the rectangles appeared slanted than when a depth step was perceived, indicating that perspective information also plays a role in biasing slant percepts (experiment 2). Visual direction measurements of the outer edges of the flanking rectangles indicate that the visual system displaces a portion of the non-fixated plane to fit all monocular features into a single cyclopean view (Mapp & Ono 1999Vision Research 39 2381-2386) (experiment 3).
Chapter 3 reports on an experiment measuring the spatial extent over which significant interocular transfer of the motion aftereffect occurs. It has been argued that the angular extent over which the field of view is served by binocular neurons in the visual cortex is limited to the central 40 degrees of the binocular visual field. This argument is based on data collected with static stimuli. Here we extend this investigation to include dynamic stimuli. Interocular transfer of the motion aftereffect was measured at three eccentricities, +/-2.5, 25, and 31 degrees. Substantial interocular transfer, expressed as a percentage of monocular adapt/test MAE duration was observed at all eccentricities tested. The spatial extent of binocular interaction is likely stimulus specific. Specific definitions are in order when making claims about the spatial extent of the effective binocular field.