Flashcards in Intro 1-Visual Perception Deck (102)
What is the anatomy of the human eye?
2.5cm diameter. Lens. Fovea . Retinal landmarks. Retina. Sclera. Macula. Optic disc. Optic nerve. Optical system
What is the fovea?
Central vision, highest acuity. Most detailed vision
What is the retina?
Light sensitive surface on 75% of inner eye
What is the sclera?
Outer layer of eye. Tough fibrous coat
What is the disease of the macula?
Macular degeneration-deterioration of retina in macula (fovea). Irreversible blindness/loss of central vision
What is the optic disc?
Blind, usually unaware as corresponds with 'seeing' retina in other
What is the optic system?
Iris, pupil, cornea, ciliary muscle
What is light?
Electromagnetic energy, measured in wavelengths (visible light is 400-700nm)
What is the 1st transformation in the visual process?
Transform light into retinal image. Inverted object representation on retina. Focus-ciliary muscles tighten and relax to change thickness of lens to bend light to fill the fovea. The problem is there is a fixed distance between lens and retina
What is accommodation in the visual process?
Process where the eye changes optical power to focus on an object as distance varies. There is an accommodation limit which increases with age
What is accommodation to a far target?
Relaxed ciliary muscles-slim lens (slight curvature so light is only bent a little). Focus point on fovea-image is sharp. Near target-focus point behind retina-image is blurred
What is accommodation to a near target?
Tightened ciliary muscles-thick lens (much curvature so light is bend a lot). Focus point on fovea-image is sharp. Far target-focus point before retina-image is blurred
What are two common visual problems?
Myopia and hyperopia
What is myopia?
Nearsightedness. Lens is too thick so bends light too much, or the eyeball is too long. Requires concave corrected lenses
What is hyperopia?
Farsightedness. Eyeball is too short. Requires convex correction lenses
What is the second transformation in the visual process?
Transduction-image on retina transformed into electrical energy. Light eaves move down from ganglion cell to the photo receptors (rods and cones). Optic disc=blind spot (no photo receptors at that retinal location
How do rods and cones differ?
120 million rods compared to 6 million cones. Cones adapt to dark quicker but rods are more through. Higher sensitivity in rods (dark adapted eye). Better visual acuity in cones (light adapted eye). More convergence of rods, increasing sensitivity. Less convergence in cones increases acuity. Rods more sensitive to shorter wavelengths, and cones to long. Purkinje shift. Rods operate at low luminance (no colour sensation). Cones operate at high luminance (s cones blue, m cones green, l cones red)
What are two types of vision?
Photopic vision (cone dominated) and scotopic vision (rod dominated). Furthermore, mesopic vision is rod and cone vision together
What is ganglion cell input?
Neural convergence-receives input from 126 photo receptors which excites or inhibits ganglion cell depending on where in ganglion's receptive field the stimulus is
What is the receptive field of a neuron?
Part in visual field which stimulus is able to modify firing rate of this neuron
What are the excitatory and inhibitory areas?
Excitatory area ('on' area) increases firing rate. Inhibitory area ('off' area) decreases firing rate
What are the three main types of ganglion cells?
Magnocellular (M) cells (most input from rods, not colour specific). Parvocellular (P) cells (input from single M or L cones-colour specific to green/red on/off). Koniocellular (K) cells (excitatory input from S cones and inhibitory inout from M and L cones-blue on)
What are the parts of the retinogeniculostriate pathway?
Retina, lateral geniculate nucleus and striate visual cortex
What is lateralisation of vision?
Optic chiasm-nasal axons cross over to other side of brain-temporal axons stay on the same side. Visual fields now represented in contralateral hemisphere
What are the layers of the geniculate nucleus?
6 layers with axons from P neurons (top four layers), M neurons (bottom two layers), and K neurons
What is the visual cortex?
Primary visual cortex-v1-striate visual cortex. Extrastriate visual areas-v2/v3/v4/v5 (midle temproal area) and IT (inferotemporal cortex)
What happens when visual information travels through cortex?
Ongoing neural convergence. Neurons' receptive fields increase. Visual information gets more and more complex-ongoing integration
What is v1?
Striate cortex. Magno/parvo areas from LGN/retina preserved in v1 input layers but merge subsequently. Some v1 neurons are orientation selective (elongates receptive fields to capture edges in particular orientation). Receptive field not stimulated or with non-preferred orientation will not cause a response. v1 Single cell recording (Hubel and Wiesel). Other neurons are motion direction selective or selective for colour/brightness
What is v2?
Receptive fields twice as large as v1. Respond to basic stimulus features and more complex ones?