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University of Toronto Scarborough
Steve Joordens

Roshan Singh 120507 Mr. Joordens PSYA01H3 Chapter 7 Notes The primary function of the sense organs is to provide information to guide behaviour. Perception A rapid, automatic, unconscious process by which we recognize what is represented by the information provided by our sense organs. We do not first see the object and then perceive it; we simply perceive the object. The ambiguous objects that require some research are more similar to problem solving than perception. Visual perception takes place in the brain. The optic nerves send visual information to the thalamus, which relays information to the primary visual cortex, located in the occipital lobe at the back of the brain. In turn, neurons in the primary visual cortex send visual information to 2 successive levels of the visual association cortex. The first level, located in the occipital lobe, surrounds the primary visual cortex. The second level is divided into 2 parts, one in the middle of the parietal lobe and one in the lower part of the temporal lobe. Visual perception by the brain is usually described as a hierarchy of information processing. The higher levels of the perceptual process interact with memories: the viewer recognizes familiar objects and learns the appearance of new ones. David Hubel and Torsten Wiesel inserted microelectrodes (small wires with microscopically sharp points) into the various visual systems of cats and monkeys to observe the action potentials produced by individual neurons. They concluded from their research that the geography of the visual field is retained in the primary visual cortex. The map is like a mosaic i.e. a picture made of individual tiles or pieces of glass. Each tile or module consists of a block of tissue, approximately .5 x .7 mm in size and containing approximately 150 000 neurons. The primary visual cortex contains approximately 2500 of these modules. Hubel and Wiesel found that neural circuits within each module analyzed various characteristics of their own particular part of the visual field. Receptive field That portion of the visual field in which the presentation of visual stimuli will produce an alteration in the firing rate of a particular neuron. Some detected lines passing through the region, some detected thickness while some detected colours. The neuron responds when a line oriented at 50 degrees to the vertical is placed in this location and has very little response when a line having 70 or 30 degree orientation is passed through the receptive field. The combination of the visual information in different modules occurs in the visual association cortex. The first level of the visual association cortex contains several subdivisions, each of which contains a map of the visual scene. Each subdivision receives information from different types of neural circuits within the modules of the primary visual cortex. One subdivision receives information about the orientation and widths of lines and edges and is involved in perception of shapes. Another subdivision receives
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