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CU-Boulder PSYC 2012 - bio psych lecture 15 notes

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3/10/15 – Lecture 15 – The Visual System and Visual Processing- Goal: to find out how information from the eyes is processed in the brain- The different functions of the ventral and dorsal streamso Ventral Stream and Temporal Cortex – the “what” path, object identification processingo Dorsal Stream and Parietal Cortex – the “where” path, understanding spatial location- Identification in the Visual Worldo Ventral Stream – WHAT pathway 3 Processing Components- Form or Shapeo Retinal Ganglion Cell Receptive Field Each retinal ganglion cell receives input from a number of nearby bipolar cells, which receive input from a number of nearby photoreceptors- Photoreceptors -> bipolar cells -> ganglion cell Each ganglion cell has a discrete receptive field of photoreceptors which will be activate if light hits them and will then activate that ganglion cello On-Center Receptivity of Retinal Ganglion Cells On-center cell – increases firing when the fight hits the center of its receptive field- Like pixles on a computer screeno KEY POINT – each cell in the visual striate cortex receives input from several retinal ganglion cells Many ganglion cells -> combine to single LGN cell -> combine to single V1 cells Line Detection in the Visual Cortex- Input from several ganglion “spot cells” is summed and activates a single neuron in the temporal cortex- Ganglion input (providing information about spots) is translated into “lines” and “bars” in thestriate cortex- Different neurons in the striate cortex responds to slightly different orientations- Neurons responding to lines in different parts ofthe visual cortex are arranged into columns in the visual cortexo Processing Shape in the Inferior Temporal Cortex Input from the striate visual cortex is sent to the inferiortemporal cortex through the ventral stream- Fire most rapidly when the striate neurons are active together Input from the line neurons integrates onto single inferior temporal cortical neurons that the process the lines into edges and shapes Inferior temporal cortex cells therefore recognize specific shapes and are arranged in columns- Lateralization: words are processed in the left side of the brain, and faces are processed in the right sideo General objects – lefto Specific objects – right - Coloro The photoreceptors and color 3 Different Types of Cones- Blue, green, and red- Each specialized to be optimally stimulated by a particular wavelength Convergence of color information takes place in the ganglion cells and cortex similar to that of shape and allow us to add/mix input from different cones- Red and blue cones mixing their signals and creating a color of purpleo Color blindness – Dichromacy Inability to sense a specific colors Lack of one type of cone results in inability to perceive color in that range 8% men and 0.5% of women have some form of color blindness- Motiono Moving objects activate different retinal ganglion receptive fields sequentially Convergence of retinal ganglion information allows neurons in the striate cortex to identify patterns of movement similar to how it detects line- Finds information about how the object is moving in relation to speed and directiono Inferior Temporal Lobe Lesions Visual form agnosia – inability to recognize objects from their shape Achromatopsia – inability to detect any colors- Still detecting and receiving information, but cannot process it in the inferior temporal lobe Akinetopsia – inability to perceive movement or moving objects Shape, Color and Motion information is sent to other neurons in the inferior temporal cortex and integrated together- Brown, oval shaped, spinning and flying in the air = footballo Communication occurs between medial temporal lobe neurons and hippocampal memory neurons to allow us to recognize objectso Communication also occurs with the speech and language centers in the temporal lobe that allows us to name the objects Multisensory Integration – adding other sensory inputs to precisely identify- Multisensory integration centers are distributed throughout the cortex- Neurons in these areas receive multimodal inputs – they receive axons from neurons from more than one sensory modalityo May also be responsible for synesthesia (experiences one sense in the same way with another sense … music has colors and movement) or the ability to experience senses across sensory modalities Sound + movement + smell? + colors = specific objecto Dorsal Stream – WHERE pathway Location in the Striate Cortex- Axons from the LGN neurons extend to the striate cortex- Information from the top of the visual field is sent to the bottom of the striate cortex and vise versao Top and bottom are flippedo Right and left are flipped- Information from the center of the visual field is sent to the center whileinformation from the periphery is sent more anteriorlyo The fovea has a larger representation than peripheral retinal areas KEY POINT – even though the image is flipped on the axes, the topographical organization of the visual field is maintained in the neuronal organization of the nervous system Posterior Parietal Cortex- Receives visual input from the striate cortex via the dorsal “what” streamo Also sends and receives input from the motor cortex and the somatosensory cortex that allows us to locate ourselves in the space of the world “where” functions of the Posterior Parietal Cortex- Localization of objects or the body in space- Producing planned movements- Spatial Memory – remembering where objects are- Visual Attention – being able to follow or track a moving object visually What is Affected by Posterior Parietal Lesions?- Apraxia – Difficulty with many movements (more severe, more challenging)- Locating objects in space (describing where an object is)o Hemispatial neglect – neglecting one side of the body or visual field (damage in right hemisphere, paying less attention to left side visual field)- Defects in spatial memory - Remembering where objects are- Defects in visual tracking and attentiono Bottom – Up vs Top – Down Perceptual Processing Bottom-Up processing: building up a mental representation of the world based on information received by the senses and assembled through successive processing steps- All small bits of information mixed together to form a representationo Babies are the ones that have to do this most of


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