Object substitution masking reveals the continuous nature of conscious object representation
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How the visual system resolves conflicting information in the construction of a stable and coherent conscious experience remains one of the central problems of vision science. One striking example of this resolution of conflict is known as object substitution masking (OSM). OSM describes the phenomenon whereby the representation of an initially presented stimulus (the target) is replaced by the representation of a subsequently presented stimulus (the mask). OSM has been used as evidence for a visual processing mechanism that evaluates emerging object representations based on incoming perceptual input. Specifically, if incoming perceptual information is found to be discrepant with previously presented information, the prior information will be replaced by the new information such that it never enters conscious awareness. OSM has typically been investigated by the simultaneous and brief (< 50 ms) presentation of a target object surrounded by four small dots (the mask). When the four dots persist after the offset of the target object, it is common for observers to only consciously perceive the mask and not the target. Leading theories of OSM explain failures in target awareness as the result of a discrete all-or-none process in which target information is eliminated before it ever enters conscious awareness. However, OSM has to date only been assessed using forced choice methodologies. Thus, theories of OSM remain underspecified in the extent to which the target is processed before, during, and after the mechanism responsible for OSM occurs. The purpose of the experiments presented in this thesis was to understand the nature of target representation during OSM in order to understand the nature of conflict resolution in the visual processing stream during conscious object perception. In Chapter 2, OSM was found to both increase random guessing about, as well as decrease the precision of, a target object’s orientation. This finding of reduced precision provided novel evidence that OSM can impact object representations in a continuous, rather than discrete, manner. In Chapter 3, I presented target objects for durations far exceeding those of typical masking paradigms. In support of a temporal trimming account, OSM was found to reduce the perceived duration of a target (Experiment 1) and prematurely terminate the updating of a target’s orientation (Experiment 2). This finding strengthened the notion that the process responsible for OSM is continuous in nature and further demonstrated that OSM can interfere with object representations following their formation as conscious percepts. These findings challenge existing theories of OSM and argue that the process responsible for OSM is the result of a continuous, rather than discrete all-or-none, process. Further, these studies extend the reach of OSM as a tool for investigating conscious vision beyond the processes involved during the formation of a conscious representation.