Binocular rivalry in context

Abstract

In the thesis ‘binocular rivalry in context’, we discuss how binocular rivalry is affected by its visual surround. This approach enables us to answer the following question: how does a visual surround affect (local) visual perception? Several experiments described in this dissertation show that binocular rivalry can be affected by visual context. Visual context can both modulate dominance durations of rival targets and can affect the amount by which rival targets are suppressed. Visual context affected binocular rivalry in a manner closely in agreement with observations from neurophysiology. At high contrast, dominance of a rival target sharing its defining feature with the surround was lowered. At low contrast, a surround boosted the dominance of a target with the same defining feature. This finding corresponds with adaptive center-surround interactions observed at the neuronal level. In addition, these adaptive center-surround interactions are likely to be a general property of visual processing since they were observed for stimuli defined by motion, orientation and color. We have also shown that the influence of visual context on visual perception is dependent on visual attention. Dominance durations of rival targets increased when performing a task on stimuli presented in the surround. Again, this result is in accordance with results from neurophysiology: the way the neural response to a visual stimulus is affected by attention is similar to the effect of changing the contrast of the stimulus. The results provide possible insights into the following question: how does the visual system efficiently code visual information under a variety of viewing conditions? The surround interactions described in this dissertation provide a possible solution to this problem. When contrast is low, the neural signal is amplified, when contrast is high, this signal is lowered. This adaptive interaction between context and local visual information might enable us to perceive the visual world efficiently under a variety of visibility conditions. A similar argument can be made for the role of visual attention. While inspecting the visual world, we often wish to attend to multiple objects. Our experiments suggest that the signal for a stimulus increases if more attentional resources are available. The results of this dissertation also provide insights into the phenomenon of binocular rivalry. Binocular rivalry is evidently not independent of stimuli presented in the proximity of the rival targets. In addition, the results provide new insights into the relation between binocular rivalry and visual attention. Dominance durations during binocular rivalry are dependent on the amount of visual attention available for tracking binocular rivalry; diverting attention lengthens dominance durations. The results also provide an account for the limited control over binocular rivalry reported in the past. While trying to hold a target dominant by attention, the ability to do so is limited by a lower-level effect of attention, which speeds rivalry alternations. In conclusion, this dissertation provides evidence that visual context can modulate visual perception in a manner similar to how visual context affects visual processing at the neural level. Although it is generally not possible to study the influence of visual context at the level of individual neurons in humans, the results reported in this dissertation point towards a similar neural organization underlying contextual modulation of visual processing in humans as that observed in non-human species