From the blind eye to the mind’s eye: How behavioral relevance determines access to visual awareness

At any moment in time we are submerged in an overwhelming amount of visual information. If our brains were to consciously process all the information reaching our eyes, it would take us a lifetime just to read this sentence. Fortunately, part of the information that reaches our eyes enjoys a privileged position: it is summarized into a single coherent subjective experience, which we refer to as (visual) consciousness. Considering that our consciousness eventually only has access to a small part of the total visual input, this raises the question what part of our visual world reaches consciousness. A method derived from interocular competition (reviewed in Chapter 3) was used to compare the propensity of visual input to reach conscious access. In this method, a high contrast dynamic pattern is presented to one eye, which temporarily suppresses from consciousness the visual input presented to the other eye. As the ocular dominance will eventually switch, the time it takes for observers to detect the initially suppressed image provides a measure of this image’s potency to reach conscious access. In this dissertation, I demonstrated that visual input that is relevant to the observer gains privileged access to consciousness. For instance, visual input that is relevant for a concurrent task gains consciousness access about 14% faster than the same visual input when it is not relevant for this concurrent task (Chapters 5-7). Similarly, visual input that signals an upcoming aversive event (i.e., an electric shock) gains conscious access about 19% faster than similar visual input that does not signal an upcoming aversive event (Chapter 4). How does the visual system privilege behaviorally relevant information? The results provided in this dissertation demonstrate that, in order for the visual system to privilege behaviorally relevant visual input, behavioral relevance should first be consciously attributed to a visual feature (Chapters 1 & 2). In Chapter 6, Different computational models were compared in their potency to explain the difference in response times (reflecting conscious access) between behaviorally relevant and irrelevant visual input. The response time data was best explained by an a priori bias, rather than greater perceptual fluency, in favor of behaviorally relevant visual information. Together, these observations suggest that neural populations that represent a behaviorally relevant visual feature are increasingly reactive, thereby biasing the competitive strength of visual input that matches these features. Subsequent fMRI experiments (Chapter 7) directly addressed this hypothesis. The results revealed that the neural response to visual information was enhanced, when it matched a representation that was relevant for a concurrent task. In conclusion, it appears that consciousness is needed to determine what part of our visual world is relevant to our current behavioral goals. Once behavioral relevance is attributed to particular visual features, the neural populations representing these visual features enjoy elevated activity levels. Subsequent visual input that matches these visual features is then enhanced, compared to mismatching visual input. This ultimately allows for visual information that is relevant to the behavioral goals of the observer to gain privileged access to consciousness.