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Lecture 5

Lecture 5.docx

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Dwayne Pare

THE STRUCTURE OF THE VISUAL SYSTEM Questions to Consider:  In what way can striate cortex (V1) be thought of as working like photographic paper?  What was the nature of the first stimulus that Hubel and Wiesel found success with when conducting single unit recording studies in cats?  How can we use the knowledge that striate cortex has ―line detectors‖ to begin to develop a theory of object recognition? Typoglycemia – the human mind does not read every letter by itself, but by the word as the whole. So letters can be scrambled in a word and as long as the first/last letter are in place, it can be read.  Does this actually exist? Object Recognition Why is object recognition important?  Crucial for applying your knowledge  Crucial for learning o If you couldn’t recognize objects, you couldn’t build knowledge base How do we perceive and recognize objects? Form perception: shape and size Object recognition: identification Form Perception Simple visual features  Object Recognition  Knowledge There is also a loop where our previous knowledge can help us identify or recognise an object. Necker Cube One set of visual features – but two possible interpretations. You can see both but only one at a time. Form Perception (cont.) Our perception is not just based on what is actually there to recognise/understand the object. Knowledge can change our interpretation An image can be static but it is our mind that is changing our perception People resolve ambiguity in everyday situations  Bowl of fruit example: we say that there is one apple behind the banana. It is ambiguous because it could be two apples but our brain decides no, based on previous knowledge Principles of Form Perception Your ability to interpret these scenes is governed by a few basic principles  Similarity: if things are similar, we think them to be part of/the same as one object. We tend to group similar items together.  Proximity: things that are closer together, we tend to group them with one another  Continuity: we think of things as generally continuing, even with something else obscuring it.  Closure: if we can see an entire image as a whole, it doesn’t matter if there are gaps in that form.  Simplicity: we tend to go for the easiest answer for what would make up an object With text Form Perception (cont.) Brain areas for basic visual features Brain areas for large-scale forms Interaction Object Recognition Context helps with object recognition. We can recognise objects from the front, back, and even with incomplete information. Top-Down Influences on Object Recognition Bottom-up (or data-driven) processing: Stimulus-driven effects Top-down (or concept-driven) processing: Knowledge- or expectation-driven effects (cont.) Recognition begins with features—the small elements that result from the organized perception of form Features  Building blocks  Commonalities for variable objects  Play a role in visual search Number of properties in an object can slow you down in identifying it. Integrative agnosia: Difficulty in judging how more than one feature is bound together in objects  parietal cortex damage  Disruption of parietal cortex via transcranial magnetic stimulation (TMS) Word Recognition Methodology for studying word recognition Words that are familiar are easier to recognise than words that are unfamiliar.  Familiarity: how often a word would appear in a huge text. The ones that are more frequent are probably more familiar. Priming: if we’ve previously seen the word, we are more likely to recognize it. Repet
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