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Chapter 4

Chapter 4 - Research in Psychology.doc

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Dax Urbszat

Chapter 4 – Perception and Sensation • Canadian Space Psychology is rapidly developing; includes the examination of such matters as the effects of isolated and extreme environments and the nature and effects of multicultural interactions • Study was done to show that there is a reduction in hand-eye co-ordination when up in space o While on earth, gravity gives us a cue for our judgment of up and down; however in space, there is spatial disorientation in which these judgments are much harder to make and can lead to discontinuity between sensory information derived from the vestibular system (organs in ear) o Research was done to examine the role of vision in determining the body’s position and sensory adaptation to microgravity • People rely on 3 cues: visual, gravity and body direction to establish direction of up and down • Sensation and perception: o Sensation: stimulation of sense organs; involves the absorption of energy such as light or sound waves by sensory organs (ears and eyes) o Perception: the selection, organization and interpretation of sensory input; involves organizing and translating sensory input into something meaningful such as a familiar face or other environmental stimuli Thresholds: Looking for limits • Sensations begin with a stimulus; but at what point can a stimulus be detectable to an organism? (ex. what is the minimum amount of light that a human can detect?) • A threshold is a dividing point between energy levels that do and do not have a detectable effect • an absolute threshold is the minimum amount of stimulation that an organism can detect; they define the boundaries of an organisms sensory capacity; but it does not really exist o does not really exist – ex. when a light is flashed at us at varying intensity, we do not just detect one certain intensity of light; rather as the intensity of the light increases, there’s an increase the stimulation response o therefore, the absolute threshold is the stimulus intensity at detected 50% of the time The JND • Just noticeable difference (JND) is the smallest difference in the amount of stimuli that an organism’s senses can detect • They vary by sense • Weber’s Law states that the size of the jnd is a constant proportion of the size of the initial stimulus (weber’s fraction) o As the stimuli increases in magnitude, the JND becomes larger Signal-detection theory • Signal detection theory proposes that the detection of stimuli involves decision processes as well as sensory processes, which are both influence by a variety of factors besides stimulus intensity o ex. when you are given a task to watch the radar screen, you need to use your ability to a) decide what you think is a strong stimulation (creating criterion) and b) respond to how you feel about certain intensities of a stimulaton Perception without awareness • Can sensory stimuli that fall beneath the threshold of awareness still influence behavior? • Subliminal perception: the registration of sensory input without conscious awareness • We are consciously unaware of certain messages or hidden that we see everyday, but our subconscious can pick up these messages and it can affect our actions and decisions without us knowing why • People are defenseless against appeals operating below our threshold of awareness • Subliminal inputs can produce measurable although small effects in subjects who subsequently report that they did not consciously register that stimuli • Subliminal stimulation generally produces weak effects and usually can only be detected by very precise measurements in laboratory conditions (ex. during experiments conducted specifically to find these effects) Sensory adaptation • Sensory adaptation is a gradual decline in sensitivity due to prolonged stimulation • Ex. if you stay in the kitchen without removing the garbage, you realize the stench starts to fade • Sensory adaptation is an automatic, built-in process that keeps people tuned in to the changes rather than the constants in their sensory input. It allows people to ignore the obvious and focus on changes in the environment that may signal threats to safety Our sense of sight: Our Visual System The stimulus: Light • Lights that humans normally see are mixtures of several wavelengths; it varies in purity: how varied the mix of light is; it influences perception of the saturation, or richness of colours • Vision is a filter that permits people to sense but a fraction of the real world and animals have different capabilities and live in a different world The eye: A living Optical Instrument • The eye serves two purposes: they channel light to the retina, and they house that tissue • Light enters through the cornea and with the crystalline lens, they form upside-down images of objects to the retina – the brain knows the rule for relating positions on the retina in correspondence to the positions in the world • The lens is the transparent eye structure that focuses the light rays falling on the retina; facilitates accommodation • Accommodation occurs when the curvature of the lens adjusts to alter your focus; focus on close objects, lens gets fatter; focus on far objects, lens flattens out for a better image o Nearsightedness – when close objects can be seen but far objects cant because the focus of the light falls short of the retina o Far-sightedness – when you can see far distance but not close objects because the focus of light falls behind the retina • the pupil is the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye; constricts – less light to retina, sharpens image; dilates – lets more light night, but not as sharp of an image • Saccades is the movement of the eye as it scans the visual environment; tiny movements are essential to good vision The Retina: the brain’s envoy in the eye • The retina is the neural tissue lining the inside back surface of the eye; it absorbs light, processes the image and sends visual information to the brain • The axons that run from the retina to the brain converge at the optic disk, a hole in the retina where the optic nerve fibres exit the eye – at this spot in the retina, you have a blind spot; but not in the same spot in both eyes so your one eye accounts for the blind spot in the other Visual Receptors • Retina contains millions of receptor cells that are sensitive to light; but only 10% of the light arriving at the cornea reaches the receptors • Cones are specialized visual receptors that play a key role in daylight and colour vision; better at visual acuity - sharpness and precision in detail o Concentrated heavily in the fovea: tiny spot in the center of the retina that contains only cones; visual acuity is greatest at this spot • Rods are specialized visual receptors that play a key role in night and peripheral vision; located just outside the fovea • Dark adaptation is the process in which the eyes become more sensitive to light in low illumination – declining absolute thresholds • Light adaptation is the process where the eyes become less sensitive to light at high illumination o These adaptations are caused by chemical changes in the rods and cones Information processing in the Retina • Light that triggers the receptors triggers neural signals that send impulses along the optic nerve, which is a collection of axons that connect the eye with the brain; impulses carry the visual information to the brain • The receptive field, made up of rods and cones is the part of the retina that, when stimulated, affects the firing of the cell; when stimulated, retinal cells send signals both towards the brain and laterally to nearby visual cells • Lateral antagonism occurs when neural activity in cell opposes activity in surrounding cells o Allows us to see the contrast between different intensities of light Vision and the brain • Axons leave the back of the eye to form optic nerves that travel to the optic chiasm which is the point where the optic nerves from the inside half of each eye cross over then project to the opposite half of the brain – reaches both hemispheres • After reaching the optic chiasm, the optic nerves diverge into 2 pathways: 1. To the thalamus where the axons synapse in the lateral geniculate nucleus where signals are processed and directed to the occipital lobe (primary visual cortex)- 90% of axons  Magnocellular channels and parvocellular channels are specialized pathways in the main visual pathway that engage in parallel processing that involves simultaneously extracting different kinds of information from the same input 2. To the super colliculus before they reach the thalamus and the occipital lobe; its main function is to be able to coordinate the visual input with other sensory input • There are different types of specialized cells in the brain that respond to different stimuli – feature detectors; neurons that respond selectively to very specific features of more complex stimuli • After visual input is processed in the primary visual cortex, it is routed to other cortical areas for additional processing (ex. the ventral and dorsal stream); the more along the visual processing you go, the more specialized the neurons are about what turns them on and the stimuli that activate them Multiple methods in vision research • We use magnetic resonance imaging to examine the neurological functioning of the brain • The McCollough effect is an afterimage phenomenon that differs from other colourafter image effects because it is contingent on both colour and pattern/form • Visual agnosia: the inability to recognize objects Viewing the world in colour • Perceived colour is primarily a function of the dominant wavelength in these mixtures • Wavelength is related to hue, amplitude and brightness ad purity to saturation • There are two types of color mixtures: o Subtractive colour mixing works by removing some wavelengths of light, leaving less light than was originally there (ex. overlap of two colours blocks out certain wavelenghts o Additive colour mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself • Trichromatic theory • Theory holds that the human eye has three types of receptors with differing sensitivities to different light wavelengths associated with red, blue and green • “dichromats” are people who are colour blind and there are three types of dichromats associated with insensitivity to the 3 different types of receptors • The Opponent process theory o This theory holds that colour perception depends on receptors that make antagonistic responses to three pairs of colours (red vs. green, blue vs. yellow, black vs. white) o This explains the complementary afterimages and the need for four names when we are trying to describe the colour
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