Chapter 4: Perception and Sensation

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Chapter 4: Perception and Sensation by Mind Map: Chapter 4: Perception and Sensation

1. 4.1 Sensory Systems

1.1. HOW WE SENSE: the first step in sensation involves accessory structures (eg - lens of the eyes, that modify a stimulus). The second step is transduction, which is the process of converting incoming energy into neural activity

1.1.1. ELEMENTS OF A SENSORY SYSTEM: Energy (contains information about the world --> Accessory structure modifies energy --> Receptor transduces energy into neural activity --> Sensory nerves transfer the neural activity to the central nervous system --> Thalamus processes and relays the neural activity to the cerebral cortex --> Cerebral cortex receives input and produces the sensation and perception

1.2. PSYCHOPHYSICS: an area of research focusing on the relationship between the physical characteristics of environmental stimuli and the psychological experiences those stimuli produce

1.3. ABSOLUTE THRESHOLDS: how strong a stimulus must be to trigger a conscious perceptual experience. Stimulation that is below this threshold that is too weak/brief to notice is generally referred to as subliminal stimulation. Stimulus above is supraliminal stimulation

1.3.1. Vision - a candle flame seen at 48km away on a clear night

1.3.2. Hearing - the tick of a watch from 6m away

1.3.3. Taste - one teaspoon of sugar in 7.5L of water

1.3.4. Smell - one drop of perfume diffused into the entire volume of air in a six-room apartment

1.3.5. Touch - the wing of a fly falling on your cheek from a distance of 1cm

1.4. SIGNAL DETECTION THEORY: a mathematical model of what determines a person's report of a near-threshold experience

1.5. JUDGING DIFFERENCES: the smallest detectable difference in stimulus energy is known as the difference threshold, or the just-noticeable difference (JND)

1.5.1. Weber's law - states that the smallest detectable difference in stimulus energy is a constant fraction of the intensity of the stimulus

1.6. SENSE - a system that translates information from outside the nervous system into neural activity. SENSATIONS - messages from the senses that make up the raw information that affects many kinds of behaviour and mental processes ENCODING - translating the physical properties of a stimulus into a pattern of nerve cell activity that specifically identifies those properies

1.6.1. NEURAL RECEPTORS - specialised cells that detect certain forms of energy and transduce them into nerve cell activity. TRANSDUCTION - the process of converting incoming energy into neural activity SENSORY ADAPTATION - the process through which responsiveness to an unchanging stimulus decreases over time PSYCHOPHYSICS - an area of research focusing on the relationship between the physical characteristics of environmental stimuli and the psychological experiences those stimuli produce SIGNAL DETECTION THEORY - a mathematical model of how your personal sensitivity and response bias combine to determine your decision about whether or not a near-threshold stimulus occured JUDGING DIFFERENCES - the just-noticeable difference (Weber's law) is the smallest difference between stimuli that we can detect MAGNITUDE ESTIMATION - the perception of stimulus intensity is related to the actual strength (Fechner's law)

2. 4.2 Hearing

2.1. SOUND: the physical dimensions of sound - 1. amplitude is the difference between the peak and the baseline of a waveform 2. the distance from one wave peak to the next is called the wavelength 3. frequency is the number of complete waveforms or cycles, that pass a given point in space every second

2.1.1. SOUND: psychological dimensions of sound - 1. loudness is a psychological dimension of sound determined by the amplitude of a sound wave 2. pitch is how high or low a tone sounds 3. absolute pitch is the ability to identify the musical notes associated with specific sound frequencies 4. timbre is the mixture of frequencies and amplitudes that make up quality of sound

2.2. THE EAR: the human ear converts sound energy into never cell activity through a series of accessory structures and transduction mechanisms

2.2.1. Auditory accessory structures - sound waves are collected in the outer ear (pinnea) and is funnelled down the ear canal to the ear drum (tympanic membrane). The vibrations through the tympanic membrane pass through a chain of 3 tiny bones (malleus/hammer, incus/anvil, and stapes/stirrup) which amplify the vibrations, focusing them onto a smaller membrane called the oval window Auditory transduction - after passing through the oval window, they enter the inner ear to the cochlea (where transduction occurs). It is lined with the basilar membrane, which is a liquid that runs through the cochlea. This contains a bundle of axons (the acoustic nerve) that carries stimuli from the hair cells of the cochlea to the brain Auditory pathways, representations and experiences - before sounds can be heard, the information is sent to the brain for further analysis (thalamus). It is then relayed to the primary auditory cortex, in the temporal lobe of the brain

2.3. SOUND: pressure fluctuations of air produced by vibrations -- the amplitude, frequency, and complexity of sound waves determine the loudness, pitch and timbre of sounds

2.3.1. EAR: pinna, tympanic membrane, malleus, incus, stapes, oval window, basilar membrane -- changes in pressure produced by the original wave are amplified HAIR CELLS OF THE ORGAN OF CORTI -- frequencies are coded by the location of the hair cells receiving the greatest stimulation (place theory) and by the firing rate of neurons (frequency-matching, or volley theory) ACOUSTIC NERVE TO THALAMUS TO AUDITORY CORTEX -- auditory cortex decodes patterns of information from the acoustic nerve, creating sensations of loudness, pitch, and timbre

3. 4.3 Vision

3.1. LIGHT: visible light is electromagnetic radiation that has a wavelength of approx. 400-750 nanometres. Light intensity is a physical dimension of light waves referring to how much energy the light contains; it determines the brightness of light.

3.2. FOCUSING LIGHT: the light rays enter the eye by passing through a transparent protective layer (cornea) --> passes through the pupil --> the iris adjusts the amount of light allowed into the eye -->the cornea and lens are curved which bends the light rays --> the light rays are focused at the back of the eye on the retina --> the lens bends light rays entering the eye from various angles to meet onto the retina

3.2.1. the ability to change the shape of the lens to bend light rays is called ocular accomodation

3.3. CONVERTING LIGHT INTO IMAGES: photoreceptors are specialised cells in the retina that convert light energy into nerve cell activity. They contain photopigments, which are chemicals that respond to light --> when light strikes one it breaks --> after one breaks, new molecules are created

3.3.1. rods and cones - rods contain rhodospin, whereas cones contain 3 types of iodopsin. Rods have only one pigment, so they respond equally to all wavelengths, meaning they can't help discriminate between colours and are more sensitive to the light. Cones are colour sensitive and become more active in brighter light. cones are located in the centre of the retina, in a region called the fovea, where the eye focuses light from looking at objects. they are highly dense here, allowing us to see details. there are no rods in the human fovea. away from the fovea, the more rods there are.

3.4. FROM THE RETINA TO THE BRAIN: the optic nerve carries visual information to the brain

3.5. SEEING COLOUR: most colours are a mixture of light of different wavelengths. hue, saturation, and brightness determine our sensation of colours - hue is the essential 'colour' determined by the dominant wavelength of light, colour saturation the purity of a colour, brightness is the overall intensity of all the wavelengths that make up light

3.5.1. the trichromatic theory of colour is a theory of colour vision identifying 3 types of visual elements, each of which is most sensitive to different wavelengths of light the opponent-process theory of colour vision - is a theory of colour vision stating that colour sensitive elements are grouped into red-green, blue-yellow, and black-white elements the bottom line of colour vision - we see colour because our 3 types of cones have different sensitivities to different wavelengths. we sense different colours when the 3 cone types are stimulated in different ratios. because there are 3 types of cones, any colour can be produced by mixing 3 pure wavelengths of light - but there is no more than that

3.6. INTERACTIONS OF THE SENSES: SYNAESTHESIA: the blending of sensory experience that causes some people to 'see' sounds or 'taste' colours

3.7. ENERGY: light - electromagnetic radiation from about 400nanometres to about 750nanometres -- the intensity and wavelength of light waves determine the brightness and colour of visual sensations

3.7.1. ACCESSORY STRUCTURES: eye - cornea, pupil, iris, lens -- light rays are bent to focus on the retina TRANSDUCTION MECHANISM: photoreceptors (rods and cones) in the retina -- rods are more sensitive to light, but cones discriminate among colours. Cones respond differently to different light wavelengths. The sensation of contrast is enhanced through interactions among cells of the retina reaching photoreceptors PATHWAYS AND REPRESENTATIONS: optic nerve to optic chiasm to lateral geniculate nucleus of thalamus to visual cortex -- neighbouring points in the visual world are represented at neighbouring points in the LGN and visual cortex. Neurons respond to aspects of the visual stimulus - eg, colour, movement, distance, form

4. 4.6 Perception

4.1. THE PERCEPTION PARADOX: perception can often take place automatically, without being consciously aware of it (eg: drivers slowing in response to lines on the road).

4.1.1. Perceptual failures - these are cases in which our perceptual experience of a stimulus differs from the actual characteristics of that stimulus. These provide clues to the problems that our perception systems must solve and their solutions.

4.2. THREE APPROACHES TO PERCEPTION: 1. computation model - an approach to perception that focuses on how computations by the nervous system translate raw sensory stimulation into an experience of reality 2. constructivist approach - an approach to perception taken by those who argue that the perceptual system uses fragments of sensory information to construct an image of reality 3. ecological approach - an approach to perception maintaining that humans and other species are so well adapted to their natural environment that many aspects of the world are perceived without requiring higher-level analysis and inferences

4.3. COMPUTATIONAL MODEL: an approach to perception that focuses on how computations by the nervous system translate raw sensory stimulation into an experience of reality

4.3.1. CONSTRUCTIVIST APPROACH: an approach to perception taken by those who argue that the perceptual system uses fragments of sensory information to construct an image of reality ECOLOGICAL APPROACH: an approach to perception maintaining that humans and other species are so well adapted to their natural environment that many aspects of the world are perceived without requiring higher-level analysis and inferences

5. 4.7 Organising the Perceptual World

5.1. - perceptual organisation: the task of determining what edges and other stimuli go together to form an object

5.2. BASIC PROCESSES IN PERCEPTUAL ORGANISATION 1. figure ground discrimination - the ability to organise a visual scene so that it contains meaningful figures set against a less relevant ground (eg: reversible images)

5.2.1. 2. grouping - to distinguish figure from ground, our perceptual system must first identify elements in the environment. Principles of the Gestalt laws: proximity, similarity, continuity, closure, texture, simplicity, common fate. These were added: synchrony, common region, connectedness

5.3. PERCEPTION OF LOCATION AND DISTANCE: two dimensional location involves recognising if something is to your right or left. Depth perception is the ability to perceive its distance away from you

5.3.1. motion parallax - a depth cue whereby a difference in the apparent rate of movement of different objects provides information about the relative distance of those objects eye convergence - a depth cue involving the rotation of the eyes to project the image of an object on each retina retinal disparity - a depth cue based on the difference between 2 different retinal images

5.4. PERCEPTION OF MOTION: looming is a motion cue involving a rapid expansion in the size of an image so that it fills the retina. Sometimes we perceive motion when there is none

5.5. PERCEPTUAL CONSISTENCY: this is the perception of objects as constant in size, shape, colour and other properties despite changes in their retinal image

5.5.1. size constancy - as an object moves closer or we move closer to it, the size of its retinal image increases yet the perceived distance decreases at the same rate = the perceived size of the object remains constant shape constancy - similar to size constancy. The brain automatically combines information about retinal images and distance as movement occurs. brightness constancy - even with dramatic changes in the amount of light striking an object, our perception of the object's brightness remains relatively constant

5.6. FIGURE GROUND DISCRIMINATION: certain objects or sounds are automatically identified as figures, whereas others become meaningless background -- you see a person standing against a building, not a building with a person-shaped hole in it

5.6.1. GROUPING: properties of stimuli lead us to automatically group them together. These include proximity, similarity, continuity, closure, texture, simplicity, common fate, synchrony, common region and connectedness -- people who are sitting together or who are dressed similarly are perceived as a group PERCEPTION OF LOCATION AND DEPTH: knowing an object's two dimensional position (left/right) and distance enables us to locate it. Information about its 2D position is provided through the retina and orientation of the head. Depth or distance perception uses stimulus cues such as interposition, relative size, height in the visual field, gradient of texture, linear perspective, clarity, colour, shadow -- a person who looks tiny and appears high in the visual field is perceived as being of normal size but at a great distance PERCEPTUAL CONSTANCY: objects are perceived as constant in size, shape, brightness, colour, and other properties, despite changes in their retinal images -- a train coming towards you is perceived as getting closer, not larger; a restaurant sign is perceived as rotating, not changing shape

6. 4.8 Recognising the Perceptual World

6.1. BOTTOM-UP PROCESSING: aspects of recognition that depend first on the information about the stimulus that comes to the brain from the sensory receptors

6.2. TOP-DOWN PROCESSING: aspects of recognition that are guided by higher-level cognitive processes and psychological factors such as expectations

6.2.1. schemas - mental representations (generalisations) of categories of objects, events, and people

6.3. NETWORK PROCESSING: explanation of various objects taking a computational appraoch

6.3.1. parallel distributed processing (PDP) - a theoretical model of object recognition in which various elements of the object are thought to be simultaneously analysed by several widely distributed but connected neural units in the brain

6.4. CULTURE, EXPERIENCE, PERCEPTION: perception can vary if people's experiences have created differing expectations and other knowledge-based top-down processes

6.5. BOTTOM-UP PROCESSING: raw sensations from the eye or ear are analysed into basic features, such as form, colour, or movement; these features are then recombined at higher brain centres, where they are compared with stored information about objects or sounds -- you recognise a dog as a dog because of its features, (barking, 4 legs, panting) which match your perceptual category for 'dog;

6.5.1. TOP-DOWN PROCESSING: knowledge of the world and experience in perceiving allow people to make inferences about the identity of stimuli, even when the quality of raw sensory information is low -- on a dark night, what you see as a small, vague, blob pulling on the end of a leash is recognised as a dog because the stimulus occurs at a location, where you would expect a dog to be NETWORK, OR PDP, PROCESSING: recognition depends on communication among feature analysis systems operating simultaneously and enlightened by past experience -- a dog standing behind a picket fence will be recognised as a dog even through each disjointed slice of the stimulus may not look like a dog

7. 4.9 Attention

7.1. attention is the process of directing and focusing psychological resources to enhance perception, performance, and mental experiences

7.2. DIRECTING ATTENTION: shifting attention involves 'overt orienting' (pointing sensory systems at a particular stimulus). 'Covert orienting' is being able to shift attention to an image in your mind - without having to move a muscle

7.2.1. control over attention can be voluntary or involuntary. voluntary, or goal-directed control occurs when you purposely focus your attention in order to perform a task (such as listening to your name being called or watching for a friend in a crowd). Voluntary control reflects top-down processing, as it is guided by intentions, beliefs, expectations, motivation, etc some aspects of the environment (such as a loud noise) may divert your attention, which can be said as involuntary. In such cases, attentional control is a bottom-up or stimulus driven process. Stimulus characteristics that tend to capture attention include sudden changes in lighting or colour, movement, the appearance of unusual shapes

7.3. IGNORING INFORMATION: when the spotlight of your attention is voluntarily or involuntarily focused on one part of the environment, you may ignore or be 'blind' to stimuli occurring in other parts (this is called in-attentional blindness)

7.4. DIVIDED ATTENTION: people can divide their attention in ways that allow them to do more than one thing at a time (multitasking). eg: drive, listen to the radio, sing along, and drum on the steering wheel

7.4.1. when one task is 'automatic' that it requires little to no attention, it is usually easy to do something else at the same time

7.5. ATTENTION AND AUTOMATIC PROCESSING: our ability to search for targets rapidly and automatically is called parallel processing

7.6. ATTENTION AND THE BRAIN: there is evidence of the work of directing attention to a task in brain activity. such evidence has been provided in PET scans and MRI scans, which reveal increased blood flow and greater nerve cell activity in regions of the brain associated with the mental processing necessary for the task

7.6.1. because attention appears to be a linked set of resources that improve information processing at several levels and locations in the brain, it is not surprising that no single brain region has been identified as an 'attention centre'

7.7. DIRECTING ATTENTION: you can direct your perceptual systems towards different aspects of your external and internal environments by overt orienting - pointing sensory systems at a particular stimulus - or by shifting attention without having to move a muscle - called covert orienting

7.7.1. IGNORING INFORMATION: in-attentional blindness is where your attention is voluntarily or involuntarily focused on one part of the environment; you may ignore, or be 'blind' to, stimuli occurring in other parts DIVIDED ATTENTION: multitasking is the process whereby we divide our attention, which is thought to be limited ATTENTION AND AUTOMATIC PROCESSING: our ability to search for targets rapidly and automatically is called parallel processing. Colour recognition is so automatic, it is thought that colour is analysed before the point at which attention is required