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| Question | Answer |
| What is the perceptual process? | A highly complex system, enabling us to sense our environment by using sensors (aka detectors, receptors) |
| What does the perceptual process enable us to do? | We are able to: - Locate, describe and identify all objects in our environment. - Travel between any two points, avoiding any obstacles. - Consciously experience our environment |
| What is an environmental stimulus? | An object in the environment that observers selectively attend to. The stimulus affects our receptors. |
| What is a distal stimulus? | A stimulus in the environment, usually at a distance from the observer. |
| What is a proximal stimulus? | A stimulus that stimulates the receptors. i.e. image on the retina |
| Perceptions are based on..... | ...representations of stimulus that are formed on the receptors, as well as the activity in a person's nervous system. |
| How do we perceive an environmental stimulus? | Reflected light is transformed as it is focused by the eyes optical system (cornea and lens). A sharp image is created on the receptors of the retina |
| What are sensory receptors? | Specialised cells which respond to environmental energy. |
| What is Transduction? | Environmental energy (light energy) that is changed into electrical energy (nerve impulses) |
| What are the steps of behavioural response? |
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| What are the two kinds of information a perceiver brings to a situation? | - Bottom-up (data-based) processing Based on incoming stimuli from the environment. & - Top-down (knowledge-based) processing Based on the perceivers previous knowledge (cognitive factors) |
| How do eyes enable us to see? | Light enters the eye through the pupil. The light is focused by the cornea and lens to a sharp image on the retina → flat, inverted image |
| How does the pupil work? | • Controls the amount of light entering the eye • Size of pupil: – depends on the light level • plus excitement, fear, etc. – determines the depth of the visual field |
| What are the parts of the eye? |
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| How does the cornea and lens affect how we see? | • The cornea accounts for about 80% of focusing of light rays by the eye – fixed structure • The lens accounts for the other 20% – adjusts shape for object distance |
| What is accommodation? | – The shape of the lens changes as the ciliary muscles at the front of the eye tighten and increase the curvature of the lens → the lens gets thicker – Light rays pass through the lens more sharply and focus near objects on the retina – Increases the focusing power of the lens |
| What is the Retina? | A network of neurons lining the back of the eye • Contains the receptors for vision – These contain visual pigment |
| What are the two types of receptors in the human retina? | – rods: about 120 million – cones: about 6 million |
| What are the shapes of rods and cones? |
– Rods: large and cylindrical
– Cones: small and tapered
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| How do rods and cones send signals? | Rods and cones send signals vertically through – bipolar cells – ganglion cells – ganglion axons |
| What is convergence? | When two or more neurons synapse onto a single neuron |
| Which has more convergence? Rods or cones? | Rods have more convergence than cones – Average of 120 rods to one ganglion cell – Average of six cones to one ganglion cell – Cones in fovea have one-to-one relation to ganglion cells (no convergence) |
| What are cones responsible for? | – process vision in bright light – used for fine detail – colour vision |
| What are rods responsible for? | – process vision in dim light |
| What is the rods and cones distribution in fovea? | Cones are the only receptors in the fovea – Responsible for fine detail: acuity is best in the fovea – Rods are more densely packed on either side of the fovea, then their density falls off |
| What is the distribution of rods and cones in the periphery? | • The peripheral retina has mainly rods – Acuity is worst in the periphery • There are both rods and cones in the periphery • But more rods than cones • Very few cones, but there are some |
| What is dark adaptation? | the process of increasing sensitivity in the dark |
| How does dark adaptation work? | Phase one: • Cones are more sensitive than rods at the beginning of dark adaptation • Cone sensitivity increases for 3-5 minutes • Then cone sensitivity levels off for 7-10 minutes • After about 7 minutes, rods become more sensitive than cones • Rod sensitivity increases for about 25 minutes and then levels off → i.e., rods reach their maximum sensitivity after about 25 minutes |
| What is the role of visual pigment? | The increase in sensitivity of both rods and cones during dark adaptation is caused by regeneration of the visual pigment i.e., an increase in concentration of the pigment. |
| What are the two components of visual pigment? | • Opsin: a very large protein molecule • Retinal: a smaller light-sensitive molecule |
| What is the role of the opsin molecule? | The opsin molecule separates. This causes the retina to show visual pigment bleaching: it becomes lighter in colour |
| What is the role of the retinal molecule? | The retinal molecule changes shape – i.e., isomerisation occurs |
| What is the role of isomerization? | Isomerization triggers a sequence of reactions. This sequence culminates in the generation of an electrical response in the receptor |
| How is the human eye similar to a camera? | • Both have a lens which projects an inverted image on a light-sensitive surface at the back of the enclosure • Both have an aperture that regulates how much light is admitted |
| How is the human eye different from a camera? | In the eye, the distance between the lens and the retina is fixed. The eye focuses by changing the thickness of the lens (near objects: thicker / far objects: thinner) The human eye has a single lens. It cannot bring light of all colours to a focus at the same point The eye is almost always moving. Yet we perceive the world as stable, sharp and in focus |
| How is a camera different from the human eye? | In a camera, the distance between the lens and the film is adjustable. A camera is focused by moving the lens toward or away from the film. A camera has a compound lens. It is corrected for colour: made of two kinds of glass A camera has to be kept still and steady: – Otherwise the picture is blurred |
| What is rhodopsin? | A red pigment in the retina that enables the retina to behave like a photographic plate which is continually renewed |
| What is a lens? | A long-range high-acuity instrument |
| What are lens aberrations? | Serious errors in image formation |
| What is the horseshoe crab eye design? | The limulus (horseshoe crab) has a large eye made up of hundreds of ommatidia: – Each ommatidium contains a single receptor |
| What is anableps (fish) eye design? | The anableps (a type of fish) has eyes on the top of its head • Each eye is divided into two different partsby a band of tissue – The fish floats at the water’s surface with the lower part of each eye underwater • Each eye has two pupils, connected by part of the iris |
| What is chromatic aberration? | A distortion in which a lens does not focus all colours to the same convergence point |
| How does chromatic aberration affect human vision? | The error is moderate between the red end of the spectrum and the blue-green The error increases rapidly at shorter wavelengths: the blue, violet, and ultraviolet |
| Why does chromatic aberration occur? | Because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens) |
| What is refraction? | Light changes speed as it moves from one medium to another – for example, from air into glass |
| What is chromadepth? | A system that uses colour to produce an illusion of depth. The process purposely exacerbates chromatic aberration |
| How do 3-D glasses work? | The glasses use special prismatic filters to separate an image into the visible spectrum i.e., fine lines etched onto the surface. Each colour is shifted by a different amount: this results in various planes of perceived depth |
| What is chromostereoscopy? | The use of special prismatic glasses to produce a depth effect from colour in an image |
| What is stereopsis? | The impression of depth that results from information provided by binocular disparity |
| What is the electromagnetic spectrum? | Bands of wavelengths on a spectrum measured in nm ranging from short (400nm) and long (700nm) |
| What is the wavelength of violet? | 400 to 450nm |
| What is the wavelength of blue? | 450 - 490nm |
| What is the wavelength of green? | 500 - 575nm |
| What is the wavelength of yellow? | 575 - 590nm |
| What is the wavelength of orange? | 590 - 620nm |
| What is the wavelength of red? | 620 - 700nm |
| What are solutions to chromatic aberration? | 1. Yellow lens: removes the near ultraviolet for the whole eye 2. Macular pigment: eliminates most of the violet and blue for the central retina 3. Shift from rods to cones: displaces vision in bright light toward the red |
| How does a yellow lens help to solve chromatic aberration? | It sharply cuts off the far edge of the violet, in the region of wavelength 400 nm → i.e., the region of the spectrum with the greatest error Thus: the lens solves the problem of the near ultraviolet by eliminating the region from vision - the lens filters out the ultraviolet for the whole eye |
| How does the shift from rods to cones solve chromatic aberration? | As one goes from dim to bright light, from rod to cone vision, the sensitivity of the eye shifts toward the red end of the spectrum Thus: the sensitivity of the eye moves away from the part of the spectrum with a large chromatic aberration toward the part with the least. |
| What is the purkinje shift? | enhanced sensitivity to short wavelengths during dark adaptation |
| How does macular pigment solve chromatic aberration? | Yellow pigmentation of fovea: - Like a yellow screen over the light receptors of the central retina - Takes up absorption of light on violet and blue regions of spectrum → just where absorption by lens falls to very low values • Thus: removes for the central retina the remaining regions of the spectrum (where colour error is high) |
| What is spherical aberration? | Found in all lenses bounded by spherical surfaces. Edge of lens brings light rays to a shorter focus than central lens: → the image of a point in space becomes a little “blur circle” |
| What is random variation in lens power across the pupil? | - The rays from two separate points entering the pupil may end up focused on different planes |
| What is light scatter? | The media in the eye contain tiny particles that scatter light |
| What is diffraction? | - Light paths diverge as they pass through an aperture - The pupil is an aperture and causes diffraction |
| What is featural processing? | Proposes that the visual system identifies basic features from a scene then, combines these features to construct our perceptions of the scene. |
| What are the two theories that follow featural approach? | (a) Feature Integration Theory – Developed by Anne Treisman (1987, 1993) (b) TheComputationalApproach – Developed by David Marr (1982) |
| What is feature integration theory? | Addresses the “binding problem” – How do we combine physically separate neural signals into the perception of a unified object? • Illusory conjunctions may occur due to the fast extraction of features: – Features of two objects become incorrectly combined and associated with a single object |
| What are the stages of feature integration theory? | |
| What is the computational approach? | Proposes that object perception occurs in several different stages Marr’s theory treats the visual system as if it were a computer – One which has been programmed to perceive objects |
| What is the process of the computational approach? | |
| What are pixels? | The smallest single component of a digital image: a single point The more pixels used to represent an image, the closer it resembles the original. Pixels are normally arranged in a regular two- dimensional grid |
| What is resolution? | The sharpness and clarity of an image |
| What is bit short for? | Binary Digit |
| What is a bit? | The smallest unit of information on a machine – More meaningful information is obtained by combining consecutive bits into larger units • e.g, a byte is composed of 8 consecutive bits |
| What are digital images useful for? | Simulating the action of visual neurons upon the retinal image. Neuron receptive fields can be represented by an array of numbers which can then be applied to the pixel intensities. |
| What are the two main approaches to studying perception? | Psychophysical and physiological |
| What are the 3 relationships between psychophysical and physiological approaches? | |
| What are the cognitive neuroscience methods? | 1. Experimental Techniques Used with Animals (Single-cell recording, Lesions and Genetic manipulations) 2. Neurology (Lesions, virtual lesions and Brain imaging techniques) 3. Computer modelling 4. Virtual reality/simulation 5. Eye-tracking 6. Naturalistic methods |
| What is single-cell recording? | A thin electrode is inserted into an animal’s brain: if the electrode is in the vicinity of a neuronal membrane, electrical changes can be measured Most recording is done extracellularly: electrode is located on the outside of the neuron It is very hard to record intracellularly |
| How are lesions used as an experimental technique? | Study how behaviour is altered by selectively removing one or more subcortical nuclei or distinct cortical areas |
| What are genetic manipulations? | Many aspects of cognitive functioning are heritable. The genome sequence has been mapped out for many species (including humans) |
| What is the 'knock-out' procedure? | manipulating specific genes so they are no longer present or expressed e.g. altered hippocampal cells: impaired learning and memory (like lesion method but at a microscopic level) |
| What is a CAT scan? | Computed Tomography: X-rays are projected through the head and a 3-D image based on tissue density is obtained. Sometimes a contrast material (iodine or barium) is used. A series of x‐ray photos taken from multiple perspectives are combined in a computer to produce high resolution 3-D images |
| What is MRI? | Magnetic Resonance Imaging: Many organic elements are magnetic - e.g., hydrogen. When an external magnetic field is applied, the elements become aligned: Since the density of hydrogen atoms is different in white and grey matter we can see these areas in the brain |
| What is EEG? | Electroencephalography: the measurement of neural activity |
| How are metabolic signals used? | It is possible to measure / record metabolic changes in the brain which are correlated with neural activity rather than measuring the electrical activity directly |
| What is a PET scan? | Positron Emission Tomography: A person (patient or participant) is injected with a harmless radioactive tracer the tracer moves through the bloodstream. Monitoring the radioactivity measures blood flow. Regions that are most active in the brain increase their demand for oxygen and can be detected – Changes in regional cerebral blood flow (rCBF) indicate changes in brain activity |
| What is the subtraction method? | – Brain activity is determined by: • Measuring activity in a control state • Measuring activity in a stimulation state • Subtractingthecontrolactivityfromthe stimulation activity |
| What is fMRI? | Functional Magnetic Resonance Imaging (fMRI) •Measures blood flow: –Determines the activity of areas of the brain by detecting changes in the magnetic response of haemoglobin –Haemoglobin carries oxygen and contains a ferrous molecule that is magnetic –Brain activity takes up oxygen |
| Which part of the human brain responds best to faces? | Fusiform Face area (FFA) |
| Which part of the human brain responds best to places? | Parahippocampal place area (PPA) |
| Which part of the human brain responds best to bodies? | Extrastriate body area (EBA) |
| What is computer modeling used for? | Simulation: Imitates, or reproduces, a particular behaviour in an alternative medium → e.g., “driving” in a simulator • Different levels of representation possible: System, structural, cellular or molecular levels Amount of detail depends on research question(s) |
| What are some of the pros of computer modeling? | Models are explicit: In creating a simulation, the researcher has to be completely explicit: - The way the computer represents and processes information must be totally specified • Models lead to testable predictions: Novel predictions can be generated, and then tested with real brains |
| What are some of the cons of computer modelling? | Usually radically simplified models of nervous system Most models focus on narrow problems |
| What is virtual reality? | Computer-simulated 3-D environments –Users can explore, manipulate, or interact with these • A virtual environment (VE) may simulate –A real-world place: in order to create a lifelike experience •e.g., simulations for pilot or military training –An imagined world: this may differ significantly from reality •e.g., in gaming applications |
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