Neuroscience Sencory processing book notes with exam guide

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Matthias Niemeier

Neuroscience-Sensory Processing Neuroscience Exam # 3 Study Guide -Sensory Experience and Sensory Reality • Sound as we perceive it does not exist without a brain to create it. The only reason that we experience sound is that the information from the ear goes to a region of the brain that converts the neural activity into what we then perceive to be sound. • Synesthesia: the capacity to join sensory experiences across modalities. A particular sound will also produce a color or taste. • Winderickx study: provided the first evidence that normal variation in our mental world is traceable to normal variation in our genes. -Analyzing Sensory Information • The brain processes visual information in multiple ways. Some processing allows us to consciously analyze visual stimuli, whereas other processing happens unconsciously. • The brain dissects the object, analyzes the various parts separately, and then produces what appears to be a unified perception of the whole. -Anatomy of the visual system • Retina: light sensitive surface at the back of the eye consisting of neurons and photoreceptor cells. -Structure of the eye: • The cornea and lens of the eye focus light rays to project a backward, inverted image on the receptive surface, the retina. • The optic nerve conveys information from the eye o the brain. • The fovea is the region of best vision and is characterized by the densest distribution of photoreceptor cells.. • The region in the eye where the blood vessels enter ad the axons of the ganglion cells leave is called the optic disc and has no receptors and thus forms a blind spot. -Photoreceptors • Convert light energy into chemical energy and then into neural activity. • Rods: longer and cylindrically shaped at one end, more numerous than cones, and are more sensitive to dim light. They are used mainly for night vision. • Cones: shorter and have a tapered end, responsive to bright light. They are responsible for color vision and our ability to see fine detail.(have three different pigment types) • The fovea only has cones, but in lower density at either side- vision is not so sharp at edges of visual field. -Retinal Neuron Types • Retinal ganglion cells: neural cells of the retina that give rise to the optic nerve. The axons of the ganglion cells collect in a bundle at the optic disc and leavethe eye to form the optic nerve. o M-Cells: larger and receive their input primarily from rods and are sensitive to light but not to color. Found throughout the retina including the periphery where we are sensitive to movement but not color. o P-Cells: smaller and receive their input primarily from cones and are sensitive to color. Found largely in the fovea. -Visual Pathways • Optic nerves: one exiting from each eye, they are formed by the axons of ganglion cells leaving the retina. Just before entering the brain they partly cross forming the optic chiasm. • The left half of each optic nerve goes to the left side of the brain, and the right halves go to the brain’s right side. • The nasal or medial path cross to the opposite side, while the lateral or temporal go straight back on the same side. • Geniculostriate system: after entering the brain the axons of the ganglion cells separate, forming two distinct pathways. This one goes from the retinal to the LGN of the thalamus and then to layer IV of the primary visual cortex in the occipital lobes. • Tectopulvinar system: retina to the superior colliculus to the pulvinar. Geniculostriate Pathway (detailed) • Retinal ganglion cell fibers from the two eyes distribute their connections to the two LGN of the thalamus. Fibers from the left half of each retina go to the left LGN and those from the right half go to the right LGN. • Each LGN has six layers, and projections from two eyes go to different layers- layers 2,3,5 receive ipsilateral fibers and 1,4,6 receive contralateral fibers. o This serves to combine the information from the two eyes and segregate the information from the P and M ganglion cells. • P-cells go to layers 3-6 and M cells go to layers 1-2. • Layer IV of the visual cortex has sublayers, IVCa and IVCB. o IVCa-layers 1 and 2 o IVCb-layers 3-6 -Occipital Cortex • Composed of at least six different visual regions, V1-V6. V1 is the primary visual cortex or the striate cortex. • Region V1: Neurons in the blobs take part in color perception, whereas neurons in the interblobs participate in form and motion perception. • Region V2: thick stripes receive input from the movement sensitive neurons in region V1, thin stripes receive input from V1’s color sensitive neurons, pale ones receive input from V1’s form sensitive neurons. Dorsal and Ventral Visual Streams • Two pathways that originate in the striate cortex. Pathway to the temporal lobe is the ventral stream, to the parietal lobe is the dorsal stream. • Dorsal: goes to the parietal lobe ad controls visual action • Ventral: goes to temporal lobe, controls object recognition. -Location in the Visual World • The coding of location begins in the retina and is maintained throughout all the visual pathways. • Visual field: region of the visual world that is seen by the eyes, can be divided into two halves to form the left and right visual fields. • The input from the right field goes to left hemisphere and vice versa. -Coding Location in the Retina • Receptive field: the patch of the retina in which each ganglion cell responds if stimulated. It is a region of the retina on which it is possible to influence that cell’s firing, it represents the outer world as seen by a single cell. -Location in the LGN and Cortical Region V1 • The information from a receptive field retains its spatial relation when it is sent to the lateral geniculate nucleus. • The receptive fields of many retinal ganglion cells combine to form the receptive field of a single LGN cell. The receptive fields of many LGn cells combine to form the receptive field of a single V1 cell. -The Visual Corpus Callosum • Binds the two sides of the visual field at the midline. Much of the frontal lobes have callosal connections but the occipital lobes have almost none. -Seeing Shape • When visually responsive neurons encounter a particular stimulus in their visual fields, they may show either excitation or inhibition. -Processing in the Retinal Ganglion Cells • Cells in retina do not see shapes, they are constructed by processes in the cortex from the information ganglion cells pass on. • On center cell: spot of light falling in the central circle excites and spot of light falling in periphery inhibits. Light across the entire receptive field causes a weak increase. • Off center: the opposite. Luminance contrast: the ability of the ganglion cell to tell the brain about the amount of light hitting a certain spot on the retina compared with the average amount of light falling on the surrounding retinal region. • Info transmitted from ganglion cells emphasize regions containing differences in luminance. Areas with differences in luminance are found along edges. -Processing in the Primary Visual Cortex • Cells are maximally excited by bars of light oriented in a particular direction rather than by spots of light-orientation detectors. • Simple visual cortex cells: respond to a bar of light in a particular orientation such as horizontal or oblique. The position of the bar in the visual field is important because the
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