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Chapter 6

Psychology chapter 6.doc

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Steve Joordens

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Psychology- The study of human behaviour Chapter 6 Perception Perception is the process in which we recognize what is being represented by the sensory organs. • Perception is an automatic process that occurs without our control The brain mechanisms of visual perception • According to this. step by step the surroundings are analyzed into further detail the more you go along the steps until the whole scene is perceived. Then memory kicks in and the viewer recognizes objects and learns about new objects The primary visual cortex • Hubel and Wiesel experimented on monkeys and cats in order to come to the conclusion that the retina is mapped out on the primary visual cortex • The quality or best response comes from the centre of vision, the rest of the map is made of about 2500 modules which are blocks of cortical tissue that receive information from the same group of receptor cells • Neural circuits within each module analyzed a specific aspect of vision known as the receptive field • The orientation of certain objects will increase or decrease the rate of firing of certain neurons The visual association Cortex • For us to see things in their totality, the information from the modules must be combined in the visual association cortex There are two streams of visual analysis: • Neurons of the primary visual cortex send axons to the region of the visual association cortex that surrounds the striate cortex. At this point, the visual association cortex divides into two streams: the ventral stream and the Dorsal stream • The Ventral stream continues forward and ends in the temporal cortex. It focuses on what the object is and what form and colour it has The Dorsal stream ascends into the posterior parietal cortex. It focuses on where the object is and • whether it is moving or not The Ventral Stream: Perception of Form • It is in the inferior temporal cortex that form and colour are put together to allow us to see things in 3D • Visual Agnosia is a case where people lose how to say somethings name, yet can recognize all of it features very well. This may happen due to brain damage to the visual association cortex • A symptom of visual agnosia is prosopagnosis which is the inability to recognize particular faces. they may only recognize them by voice • Studies have shown that the face recognizing circuits are found at the fusiform face area (FFA), a region of the ventral stream located at the base of the brain Tarr and Gauthier found that bird and car experts had their fusiforms activated when looking at • when they were good at but normal people did not have it activated, this signaled that the FFA be a flexible fusiform area • Gauthier and schultz suggested that people with autism do not recognize faces due to other abnormalities that tell the human that recognition is not important The extrastriate body area (EBA) is next to the primary visual cortex and is activated specifically • by photographs and drawings • Berlucchi and Aglioti found that when the EBA was deactivated, people could not recognize photos of parts of a human body, but could recognize parts of a motorcycle! • Below the hippocampus is the parahippocampal place area (PPA) and is activated by visual senses and backgrounds • In the case of visual agnosia, the PPA is undamaged allowing people to be able to recognize backgrounds well but not specific objects The Ventral Stream: Perception of Colour Cerebral achromatopsia is the loss of colour in vision without impairing the vision whatsoever • • If damage occurs only to one side of the brain, then they lose colour on only half of the visual field, however if it is bilateral, the whole visual field loses colour The Dorsal Stream: Perception of Spatial Location • Damage to the parietal cortex will lead to the inability to remember where things are and the inability to control movements of eyes and limbs • Goodale and colleagues suggested that the dorsal stream is not only responsible for where but how to pick something up. People with damage to the dorsal stream lose the ability to pick things up! The Dorsal stream: Perception of Movement • A region in the Extrastriate cortex which surrounds the primary visual cortex is responsible for responding to movement • Damage to this region of the brain can lead to the inability to recognize moving stimuli and is called Akinetopsia • Walsh and Cowet used transcranial magnetic stimulation to deactivate the region of the brain and found that people could recognize shapes but couldn’t identify which ones were moving. Form from Motion • Perception of motion can allow us to perceive three-dimensional forms in a phenomenon known as form from motion. • Johansson hooked up actors who were wearing complete black with small light bulbs at the joints and had them do exercises in the dark • People could tell if it was a human or not and could even identify the sex of the person • Grossman and colleagues found that when people viewed a video that showed form from motion, a bilateral region in the ventral bank of the posterior end of the superior temporal sulcus was activated, however no matter where the images were presented, there was more activity on the right! • Grossman and Blake found that this same region was activated even when people imagined form from motion activities! wow! Visual Perception of objects Figure and Ground • Objects are things that have particular shapes and locations in space and time • Backgrounds help us judge the locations of objects and are formless • In psychology, the terms figure and ground are used instead of object and background • The figure and ground can vary depending on what is being looked at • An important aspect of form perception is the idea of boundaries. If one exists, such as a sharp corner, we perceive an edge.If the edges form a continuous boundary then we will see it as a figure! Gestalt Laws of Perceptual Organization • This figure demonstrates illusory contours which are lines that do not exist. In the image, due to the way it is presented, we see a square on top of 4 circles • Gestalt Psychology argued that the perception of the whole is more than the sum of its individual parts. What we see depends on the relationship between the elements • The laws of grouping allow people to distinguish the figure from the background • The law of proximity states that elements that are close together will be perceived as belonging together • The law of similarity states that elements that look similar will be perceived as part of the same form • Good continuation states that when perceiving a line lets say, we normally think of it to follow the path it is currently taking and therefore it continues forever • The law of closure states that our minds often fill in slight gaps to complete the image we would like to see (law of closure is causing you to see a circle and a square) • The law of common fate states that elements that move in the same direction will be perceived as belonging to one another until one moves irregularly, similar to a chameleon camouflaging in the forest • Alias, Blake, and Lee found that the principle of common fate is not only activated by motion but contrast between two things. The higher the contrast, the more we perceive the objects to be apart Models of Pattern Perception Templates and Prototypes • Our ability to recognize shapes of objects might be explained by the use of templates which are special kinds of memories used by the visual system • While the template idea is simple, it is unrealistic in the fact that the brain would need to store possible millions of these templates making it highly un
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