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Yes

Trial-level evidence for feedback sensitivity in fixations during category learning has been previously described as weak. In this dissertation, steps were taken to overcome some methodological issues potentially obscuring the evidence for such sensitivity. Jointly, the three experiments reported here suggest that sensitivity to error in visual attention reflects cue competition, as opposed to error-driven learning of a selective visual profile. These outcomes are in agreement with previous research in human vision, which holds that fixations reflect the agent’s task representation. A case is made for the top-down control of visual attention during category learning, manifested as effects of prior knowledge, long-standing expectations, decisional uncertainty, and vacillations between alternative sources of conflicting evidence. A suggestion is made that the time-based measures of visual attention may align with the continuous ratings of the perceived category membership (reflecting learner confidence).

The eye forms through complex tissue interactions, and it still only partly understood. The developing vertebrate lens however, is crucial for coordinating eye development and eye growth, through releasing signals to surrounding eye structures. It is thought that the lens controls the growth of the eye through the production of the vitreous- the jelly-like substance that fills the main cavity of the eye and maintains the eye in its correct shape. Many components of the vitreous are produced by a region of the peripheral retina known as the ciliary body, and so it is believed that the lens controls eye growth through controlling the development of the ciliary body and thus, indirectly, the vitreous. This project addresses this concept. I have identified a previously unknown functional link between the lens and Vitamin A metabolism. The lens is important for maintaining retinoic acid production within the developing chick eye through controlling the expression of RDH10 in the presumptive ciliary body. RDH10 is important for the first step in retinoic acid synthesis, the conversion of Vitamin A into retinal, which is then converted into retinoic acid. The loss of RDH10 within the presumptive ciliary body is associated with a reduction in expression of other genes known to be involved in ciliary body development, BMP7, WNT2B and OTX1 along with a reduction in the growth of the eye. The reduction in retinoic acid production within the eye as a result of lens removal, in turn affects the synthesis of Collagen IX from the ciliary body, a major component of the vitreous. The data suggests that the lens controls retinoic acid production within the eye, through maintaining gene expression in the developing ciliary body. Retinoic acid signalling controls the synthesis of components of the vitreous, such as Collagen IX. The proper accumulation of the vitreous within the eye is crucial for the correct growth of the chick eye.

published_or_final_version / Anatomy / Master / Master of Philosophy

Visual memory has been demonstrated to play a role in both visual search and attentional prioritization in natural scenes. However, it has been studied predominantly in experimental paradigms using multiple two-dimensional images. Natural experience, however, entails prolonged immersion in a limited number of three-dimensional environments. The goal of the present experiment was to recreate circumstances comparable to natural visual experience in order to evaluate the role of scene memory in guiding eye movements in a natural environment. Subjects performed a continuous visual-search task within an immersive virtual-reality environment over three days. We found that, similar to two-dimensional contexts, viewers rapidly learn the location of objects in the environment over time, and use spatial memory to guide search. Incidental fixations did not provide obvious benefit to subsequent search, suggesting that semantic contextual cues may often be just as efficient, or that many incidentally fixated items are not held in memory in the absence of a specific task. On the third day of the experience in the environment, previous search items changed in color. These items were fixated upon with increased probability relative to control objects, suggesting that memory-guided prioritization (or Surprise) may be a robust mechanisms for attracting gaze to novel features of natural environments, in addition to task factors and simple spatial saliency. / text

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