Lecture 6 - Lisa smithson notes with some of my notes PDF

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Lisa smithson notes with some of my notes...

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Sensation and Perception Sensation and Perception ● Information comes in through our senses ● Brain interprets this information ● Sensation - stimulus detection process ○ Organs translate stimuli into nerve impulses - Transduction ● Perception - active and creative process ○ organizing and giving meaning to input ● Reception and translation of physical energies into nerve impulses ● Brain grants meaning Sensation ⇾ stimulus is received by sensory receptors ⇾ receptors translate stimulus properties into nerve impulses (transduction) ⇾ feature detectors analyze stimulus features ⇾ Stimulus features are reconstructed into neural representation ⇾ neural representation is compared with previously stored information in brain ⇾ matching process results in recognition and interpretation of stimuli ⇾ perception

Synesthesia ● Among individuals with synesthesia: ○ cross -wiring is involved ○ fMRI reveals that individuals with word-color linkages will hear certain words and respond with activity in parts of the visual cortex

Sensory Processes Transduction ● Transduction - the conversion process that transforms a stimulus into nerve impulses ● Pain transmission: ○ After nociceptors are activated, pain is transmitted along A-delta fivers or C-fibers to dorsal horn of spinal cord ○ The pain message is then sent to the brain for perception

Human senses ● More than the following “classical” senses: ○ Vision ○ Audition ○ Touch ○ Gustation ○ Olfaction Absolute Threshold ● Psychophysics - study of relationship between physical characteristics of stimuli and sensory capabilities ● Intensity at which stimulus can be detected 50% of the time ○ Lower the absolute threshold → higher sensitivity Sense Modality

Absolute Threshold

Vision

Candle flame being seen 50 km on clear, dark day

Hearing

Tick of watch under quiet conditions at 6 m

Taste

Single teaspoon of sugar in 7.5 L of water

Smell

One drop of perfume diffused into the entire volume of large apartment

Touch

Wing of fly or bee flailing on cheek from 1 cm

Signal Detection Theory ● Criteria used fluctuates; sensitivity fluctuates; depends ○ Fatigue, importance of stimulus, expectation ● Signal detection theory shows us that Perception is a decision ● Ask participants to indicate if they perceived a stimulus (e.g, heard a tone) ○ 2 conditions: stimulus present; stimulus absent ○ 4 possible outcomes: hit, miss, false alarm, correct rejection ● 50% of time, smallest difference detected; Just noticeable difference (JND) ○ Weber’s Law: JND is proportional = Weber Fraction ○ Proportion ■ For weight is about 1/50 ● Ex. For 50 gram → 1 additional gram needed ● Ex. For 500 grams → 10 grams needed ● Sensory adaptation ○ Diminishing sensitivity to unchanging stimulus ○ Occur in all sensory modalities ○ Once you use to something, you cannot experience the first time again ● Adaptive value ○ Frees senses to be more sensitive to changes in environment

Sensory Systems Vision ● Perceive small part of electromagnetic (EM) spectrum ● Light waves measured in nanometres (billionths of meter) ○ From 700 nm (reddish hue) to 400 nm (blueish hue) Structure of visual system

Anatomy of Visual System ● Cornea - transparent protective structure ● Pupil - adjustable opening that controls amount of light ● Lens - elastic structure for focusing ○ Thinner to focus on distant objects ○ Thicker to focus on nearby objects ● Retina - photoreceptors transduce light energy into electrical impulses ● Myopia ○ Nearsightedness ○ Eyeball is longer (back to front) ○ Lens focuses light in front of retina ● Hyperopia ○ Farsightedness ○ Eyeball too short ○ Lens focuses light behind retina ● Cones ○ For colour and detail ○ Function best in high illumination (creatures who function best in light have more) ○ Concentrated in centre of retina ○ Fovea (in centre of retina) contains only cones ● Rods ○ Function best in low illumination ○ 500 times more sensitive to light than cones ○ Found mostly in periphery of retina (though everywhere in retina except fovea)

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Rods and cones synapse with bipolar cells ○ Cones have ‘single line’ connection (one to one) Bipolar cells synapse with ganglion cells Axons of ganglion cells form optic nerve ○ Create ‘blind spot’ where optic nerve exits from eye

From Light to Nerve Impulses ● Visual transduction ○ Action of photopigments ○ Absorption of light changes rate of neurotransmitter release ○ Greater rate of release = the strong the signal passed on Dark Adaptation ● Rely on rods for vision in low light conditions ● Rods and cones adapt differently ○ Cones adapt after 10 min sensitivity has reached its maximum ○ Rods adapt after 30 min ○ Rods can detect light intensities 1/10 000 as great as those before dark adaptation ● Rods not sensitive to wavelengths of red light ○ Rods remain dark adapted and therefore can go from red light to dim/dark conditions Colour Vision ● Trichromatic theory (Young-Helmholtz) ○ Three types of color receptors in retina ○ Cones most sensitive to blue, green, red wavelengths ○ Visual system combines activity from these cells ○ Colours are perceived by additive mixture of impulses ○ If all are equally activated → white colour is produced ● Trichromatic theory cannot explain ○ Red-green colour-blind individuals should not be able to perceive yellow (red+green = yellow) ○ Afterimages ■ Stare at red and look away you’ll see green (same for blue and yellow) ● Opponent-Process theory (Hering, 1870) ○ Three cone types ○ Each responds to two different wavelengths ■ Red or green ■ Blue or yellow ■ Black or white ○ Explains Afterimages ■ Stare at certain colour and neural processes become fatigued ■ Have ‘rebound’ effect with receptor responding with its opponent opposite

reaction Dual Process Theory ● Combines trichromatic and opponent process theories ● 3 cone types sensitive to short (blue), medium (green), and long (red) wavelengths stimulate opponent-process reactions ● Opponent processes occur in ganglion cells. Neurons in relay stations and visual cortex Colour Deficient Vision ● Trichromats - normal colour vision ● Dichromats - deficient in one system (red-green is most common) ● Monochromat - sensitive to black-white only

Analysis and Reconstruction of visual scenes Feature detectors ● Retina ⇾ thalamus ⇾ Primary Visual Cortex ● Fire selectively ● Hubel and Wiesel studied these extensively ● Their discovery led to revolution in vision research ● Parallel processing - the ability to use our sense in a way that allows us to combine information about an object into a unified image of its properties ○ In context of vision: color, shape, distance, movement Visual association cortex ● Information from the primary visual cortex is routed to the visual association cortex ○ Object is recognized ○ We can respond to the object appropriately

Audition ● Frequency - the number of sound waves (or cycles) that occur per second; Hertz (Hz) ● Amplitude - the vertical size of the sound waves; Decibel (db) ○ Primary determinant of loudness ○ Physical pressure on eardrum Auditory Transduction ● Auditory transduction: transforming pressure waves into nerve impulses ○ Transduction system comprised of: tiny bones, membranes, liquid-filled tubes ○ These components function to transform

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pressure waves into nerve impulses Organ of corti: contains approximately 16 000 tiny hair cells (sound receptors) ○ Hair cells synapse with the auditory nerve ■ Nerve impulses are then sent to the brain

Loudness and Pitch ● Coding loudness: ○ Rate of firing in axon of auditory nerve ○ Specific hair cells involved ● Coding pitch: ○ Frequency theory - low frequencies holds this true ○ Place theory - high frequencies hold this true Localization ● Sound localization ○ Importance of 2 ears ○ Nervous system uses information regarding: time, intensity Hearing loss ● Conduction deafness ○ Involves the mechanical system that transmits sound waves to the cochlea ○ Hearing aids can help ● Nerve deafness: ○ Extremely loud sounds are the leading cause ○ Hearing aids do little to remedy this damage

Taste and Smell Gustation ● Qualities of taste: sweet, sour, salty, bitter, umami ● Taste buds: ○ Chemical receptors ○ In high concentration along the edges and back surface of the tongue ○ Humans have approximately 9000 taste buds Olfaction ● Humans have about 40 million olfactory receptors (dogs have 300 million) ● Olfactory bulb: ○ Forebrain structure ○ Odours seem to be coded according to olfactory bulb activation ● Pheromones: ○ Chemical signals in natural body scents

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May affect human behaviour ■ Menstrual synchrony

The Skin and Body Senses Sense of Touch ● 4 tactile sensations: pressure, pain, warmth, cold ● Skin is largest organ in body: contains variety of receptor structures ● Pain and temperature: free nerve ending receptors beneath skin’s surface ● Touch and pressure: nerve fivers at base of hair follicles ● Send messages to somatic-sensory cortex Pain and temperature ● Free nerve endings - primary receptors for pain and temperature ○ Nerve cells beneath skin’s surface Phantom limb phenomenon ● Amputees experience sensations coming from the missing limb Pain receptors ● Pain receptors found in all tissues of the body EXCEPT: ○ Brain ○ Bones ○ Hair ○ Nails ○ Nonliving parts of teeth Gate Control Theory ● Psychological and physical factors ○ Pain results from opening and closing of gating mechanisms ○ Spinal cord ‘gates’ send impulses to brain ○ Other sensory input blunts experience ■ Get cut, pressure on cut takes away bit of pain ○ Central control mechanisms (thoughts, emotions, beliefs) influence experience of pain ○ Endorphins - built-in analgesics (painkillers) with opiate-like properties Endorphins ● Natural opiates ● Inhibit release of NT involved in transmissions of pain from spinal cord to brain ● Acupuncture may decrease the sensation of pain by increasing the release of endorphins Sense of Kinesthesis ● Feedback about muscles and joint positions

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Receptors = nerve endings in muscles, joints, tendons ○ Inform about how body position and future coordinate movement

Vestibular Sense ● Receptors in vestibular apparatus of inner ear ○ 3 semicircular canals - receptors for head movements ■ left/right ■ back/front ■ up/down ○ Vestibular sacs ■ Respond to position of body ■ Indicate upright or at an angle

Perception Perception: Creation of Experience ● 2 kinds of processing functions ○ Bottom up processing ■ Analysis of individual stimulus elements ■ breakdown/analysis of stimuli (e.g., feature detection) ■ Re-combines into unified whole ○ Top-down processing ■ Existing knowledge, concepts, ideas, expectations ● Concept, expectation ● Guides analysis (Yes? No?) ● Interpretation of incoming stimuli ● Involves 2 processes: focusing on certain stimuli, filtering out other information ● Demonstrated in shadowing experiments ○ Listen to 2 messages delivered through earphones (one through each earphone) ○ Focus on one; ignore other ○ Can recall information from attended one; not from unattended one Environmental and Personal Factors ● Both play a role in attention ● Stimulus characteristics ● Intensity, novelty, movement, contrast, repetition

Organization and Structure of Perception Perceptual Organization ● Gestalt principles

Gestalt = pattern, shape, form ■ Wholes we perceive are more than sum of their parts ○ Suggested perception was governed by laws that determined how things were grouped together ■ Gestalt Laws of Perceptual Organization Figure-ground - simple, foreground and background Figure - distinct shape, more striking Figure-ground distinction can be ambiguous ○ Idea behind camouflage ○

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Gestalt Laws of Organization ● Similarity - similar items belong together ● Proximity - elements that are close together, belong together ● Closure - close open edges; perceive boundaries; fill gaps in incomplete figures ● Continuity - elements linked to form continuous line

Perception and Hypothesis testing ● Role of perceptual schema ○ Mental representations ○ Allows for classification of stimuli ● Perception ○ Best interpretation based on knowledge, experience Perceptual set ● Readiness to perceive stimuli in particular way ● Based on expectations and prior information ● Creates psychological context to use in top-down processing Perceptual Constancies ● Shape constancy ○ Friend’s face has a different shape when you look at their profile than face on - has friend’s face changed? ● Size constancy ○ Walk to your car - image on your retina gets larger - do you perceive your car to be growing?

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Brightness constancy ○ Colour of your jacket may be different in full sunlight than in shade

Depth perception ● Image on the retina is 2 dimensional; but we live in a 3 dimensional world ● Monocular cues - depth perceived with one eye ● Binocular cues - depth perceived with 2 eyes Monocular depth cues ● Light and shadow ● Linear perspective: parallel lines converge in distance ● Interposition: closer objects are in ‘front’ of others ● Height in horizontal plane: further objects are higher in the horizontal plane ● Texture: objects farther away have finer texture (less detail) ● Clarity: objects farther away are hazier ● Relative size: more distant objects are smaller ● Motion parallax: when we move - nearby objects move faster in opposite direction than more distance objects Binocular Depth Cues ● Have two eyes for a reason: gives exquisite depth perception ● Based on binocular disparity ○ Two eyes receive different visual images ● Feature detectors analyze differences ● Convergence: feedback from ocular muscles when focusing on something distant and then close Perception of movement ● Primary cue = image movement across retina ● Also use: movement against a background ● Apparent motion: ○ Illusion of motion ○ Stroboscopic motion (phi phenomenon) - e.g. motion pictures (series of still pictures) Illusions - Incorrect Perceptions ● Perceptual constancies show context can produce illusions ○ E.g. converging lines disrupt size constancy Perceptual Development ● Interplay of biology and experience ● Biology: newborns do not crawl onto ‘deep end;’ of visual cliff ● Experience: can adapt to ‘upside down’ environment

Critical periods ● Time period during which certain experiences must occur in order for perception to develop normally ● If visual problems are not corrected early, is there permanent problem? Restored Sensory Capacity ● Individuals born with cataracts and then had vision restored ○ Able to perceive figure-ground relationships ○ Scan objects ○ Not able to identify objects that were familiar through touch...