Sensation & Perception ch. 4 summary
Sensation & Perception ch. 4 summary
Describe the difference between sensation & perception Sensation: occurs when receptor cells in a particular sensory organ are stimulated & information is relayed to specialised centres in the brain for further processing • Biological psychology Perception: the process by which the organism selects & interprets sensory input so that it acquires meaning. Attention, organisation & interpretation are considered hallmarks of perception • Cognitive psychology Note: we are susceptible to the bias of our own perception, which is in turn influenced by our experience -‐if we expect failure, we are more likely to perceive it If we expect danger, we are more likely to perceive it -‐ultimately our perception of a situation-‐ influences emotional/behavioural response… not the object situation itself Define transduction & describe the process of how colour vision is proposed to occur Transduction: occurs as sensory receptors convert physical energy into neural impulses ! Transition from sensation to perception ! i.e raw environment data -‐-‐> meaning about our environment Sensory receptors: specialised cells that transform energy in the environment into neural impulses that can be interpreted by the brain 1. Audition (hearing): specialised cells that convert tiny movement caused by changes in air pressure into neurological signals 2. Touch: specialised receptor cells that are incredibly sensitive to pressure & to chemical stimulation 3. Olfactory (smell): specialised cells in our noses that convert molecules in our environment into neurological signals 4. Gustation (taste): specialised cells on our tongue that convert molecules into neurological signals 5. Vision: specialised receptor cells in our eyes that convert electromagnetic energy (wavelength & amplitude)
Sensation & Perception ch. 4 summary
Vision in detail • Electromagnetic energy (light) comes in various amplitudes & wavelengths • The amplitude of wave allows us to interpret the brightness • Wavelength allows us to interpret colour
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Specialised receptors in the eye allow detection of this wavelength The cornea, pupil & lens focus light on the retina. Then the retina transduces this visual image into neural impulses
Perspectives on how colour vision works 1. Ecological perspective (bottom up): environmental stimuli in our environment provide the info for perception a. Trichromatic theory: • 3 types of receptors in our retinas that are sensitive to wavelengths of primary colours (red, green, blue) • Brain is simply calculating the wavelengths a. Opponent processing theory: • After image effect • Trichromatic theory isnt enough • Not only do we have cells in our retina (trichromatic) we have antagonistic colour system-‐ black & white, blue & yellow, red & green 2. Constructivist perspective (top-‐down): perception requires more than environmental stimuli • "colour is a psychological property, not a quality of the stimulus" • Interpretation relies on visual cortex & visual area of the thalamus • Evidence: blind spot (has no receptor cells) and hence cant see a particular area
Sensation & Perception ch. 4 summary
Describe the distinction b/w bottom up & top down influences on perception Bottom-‐up processing: begins at the basic level-‐ at sensory receptors. Features are detected & then analysed & organised at a higher level ! Eg. Light is reflected off the book in front of you and focused on your retina, which converts light into neural signals, which are combined to be compared with a book Top-‐down processing: begins from the more complex level where hypotheses are formulated based on prior experiences. i.e do features detected match our hypothesis? ! Eg. A book is rectangular & has pages with dark markings, the object in front of me has these features, its probably a book **Perception uses a combination of both sensation & perception**
Understand the basic assumptions of the Gestalt approach to conscious experience, and describe 5 Gestalt laws of organisation Perceptual organisation: occurs when our brain integrates sensations into precepts (meaningful units eg. Book) & places these in a way that their meaning is accessible
1. Form perception (gestalt laws)
• Is the org of sensations into meaningful shapes & patterns • The whole is not the sum of its parts, it is not greater than its parts • Eg. Music isnt just instrument plus instrument, the composer conceives the
whole piece, the instruments are used to generate the 'gestalt quality'
Sensation & Perception ch. 4 summary
Gestalt laws: Law of simplicity: items that can be grouped and seen as whole will be seen in that way. The observer perceives the simplest patter possible
Law of proximity: elements close to each other in space or time will be perceived as groups
Law of similarity: similar items will be perceived as groups
Law of continuity: a string of items will project the probable location of the next item. i.e sees stimuli as continuous pattern/line rather than discontinuous elements
Law of closure: part of a figure that is not represented will be filled in by the perceptual system. i.e perceiving incomplete objects as complete
Law of common fate: elements of an object moving in the same direction are perceived as being more related than those that are stationary or moving in a different direction. Moving objects are likely to move at the same time, in the same direction with the same speed
Sensation & Perception ch. 4 summary
2.Depth perception (Describe the main monocular & binocular cues that contribute to
our sense of depth & perception) o Our brain must make 3D judgements about our environment based on 2D retinal image Monocular cues: o Provide info regarding depth/distance that requires sensory input of only one eye o Useful at a distance of 2D objects-‐ images Pictorial cues-‐ eg taj mahal o Linear perspective: parallel lines appear to converge in distance o Overlay/interposition: when 1 object blocks parts of another, the obstructed object is perceived as more distant o Texture gradient: textured surfaces-‐ close range= coarser, distance= finer/densely packed o Relative size: when 2 objects known to be similar size, people will perceive the smaller one as farther away o Shading: assumes light comes from above-‐ interprets shading differently at towards top & bottom o Atmospheric perspective: objects at greater distance appear fuzzier than those nearby o Ground plane position/height in plane (elevation):objects farther away appear high up towards the horizon Motion cues o Motion parallax: the relative motion of nearby objects is faster than distant objects o Kinetic depth effect: the motion of an object facilitates the perception of its depth Eye-‐generated cues o Accommodation: the change in shape of the lens in order to keep an object in focus when distance changes Binocular cues: o Dependant info regarding depth/distance that require sensory input of both eyes o Useful when objects close & 3D Eye generated cues Retinal disparity-‐ each eye sees an object from a slightly different angle. The difference b/w images can be used to cue distance Convergence-‐ movement of the eyes towards each other occurs in order to keep each focused on the object of interest. Msgs from eye muscle are sent to the CNS and distance is interpreted
Sensation & Perception ch. 4 summary
Motion cues (3. motion perception:) o Motion parallax: the relative motion of nearby object is faster than distant objects o Kinetic depth effect: the motion of an object facilitates the perception of its depth
4.Perceptual constancy (organisation of changing sensations into precepts that are stable) (Explain how the visual perception system & experience allow people to maintain a uniform view of the world by means of size & shape constancy) Perceptual constancy: the perception of stable forms, despite changes in stimulation at the receptor surface Size constancy: the ability to perceive an object as the same, despite changes in distance b/w the observer and the object o Previous experience with viewed object o The distance b/w person & object o The presence of surrounding objects Shape constancy: the ability to recognise a shape despite changes in its orientation or angle o Eg. Door opened and closed/half shut still the same shape Colour constancy: the ability to recognise a shape despite changes in its colour
Describe some of the common illusions people experience, and examine how perception may be culturally dependent Perceptual illusions: the perception of a stimulus that differs from its physical reality or what is commonly expected ! Psychologists are interested in visual illusions-‐ help explain the role of monocular cues in depth perception The Muller-‐Lyer illusion: ! ! ! • They are b oth the same length-‐ but due to our depth p erception-‐ monocular (pictorial) cues we perceive the left as being longer • Shaft that looks like the outside corner being closer (therefore shorter) than the shaft that looks like the inside corner is farther away (therefore longer) • African tribe-‐ lived in circular huts-‐ had n o perceptual experience with corners & therefore illusion didn’t work on them
Sensation & Perception ch. 4 summary
