Sensation & Perception Chapter 5 PDF

Sensation & Perception Chapter 5  Sensation? Perception? Sensation: Stimulation of the sense organs Perception: The selection, organization, and interpretation of sensory input. Psychophysics Psychophysics: The study of how phys...

Sensation & Perception Chapter 5  Sensation? Perception? Sensation: Stimulation of the sense organs Perception: The selection, organization, and interpretation of sensory input. Psychophysics Psychophysics: The study of how physical stimuli are translated into psychological experiences. Gustav Fechner (1860) – Elemente der Psychophysik Detection Stimulus: Any detectable input from the environment Absolute Threshold: For a specific type of sensory input, the minimum amount of stimulation that an organism can detect Arbitrarily defined as the stimulus intensity detected 50% of the time Detection Just Noticeable Difference Just Noticeable Difference (JND): The smallest difference in the amount of stimulation that a specific sense can detect a.k.a. Difference Threshold 500 g 505 g Weber’s Law Weber’s Law: The size of a JND is a constant (Weber fraction) that is proportional to the size of the initial stimulus. These constants differ depending on the type of sensory input! Scaling We are used to measuring things on absolute scales. e.g., distances in meters In perception, everything is relative. You can’t use absolute scales! Why? Fechner’s Law Fechner’s law Fechner’s Law states that subjective sensation is proportional to the logarithm of the stimulus intensity. This means that with constant increases in stimulus intensity, smaller and smaller increases are perceived in the magnitude of that sensation! Signal Detection Theory Signal Detection Theory proposes: Detection of stimuli involves decision processes as well as sensory processes Both processes are influenced by a variety of factors besides stimulus intensity Signal Detection Theory Perception & Awareness Subliminal Perception: The registration of sensory input without conscious awareness Started with James Vicary in 1957 – “Eat popcorn” Sensory Adaptation Sensory Adaption: A gradual decline in sensitivity due to prolonged stimulation This is an adaptive process Aware of changes in the environment rather than constants The Auditory System Sense of Hearing Sound as a Stimulus Sound waves are vibrations of molecules that travel through a medium, such as air These vibrations travel at a fraction of the speed of light Sound Waves Characterized by their amplitude, frequency, wavelength, and purity Frequency Sounds can be described in terms of their frequency, which is measured in cycles per second or hertz (Hz) Pitch depends on frequency  Wavelength Sounds can be described in terms of their wavelength, which is measured in as a distance (e.g., nm, mm, cm, m) Pitch depends on wavelength Amplitude Sounds can be described in terms of their amplitude, which is measured in decibels (dB) Loudness depends mainly on amplitude Purity Sounds can be described in terms of their purity, which is viewed as a sound envelope Timbre depends mainly on purity  Hearing Capacities Lower Frequency Upper Frequency (Hz) (Hz) Humans 20 20 000 Dogs 50 45 000 Cats 45 85 000 Bats 20 120 000 Dolphins 0.25 200 000 Elephants 5 10 000 FYI The Human Ear Three major parts of the ear: Outer (or external) ear, middle ear, and inner ear Sound is conducted differently in each Basilar Membrane  Theories of Hearing We will focus on pitch perception Perception of loudness and timbre are not yet well understood... Two main theories of Pitch Perception: Place Theory Frequency Theory  Place Theory Perception of pitch corresponds to the vibration of different portions, or places, along the basilar membrane Frequency Theory Perception of pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates Theories of Hearing Pitch perception depends on both the place and frequency coding of vibrations Low-frequency tones appear to be translated into pitch through frequency coding High-frequency pure tones appear to rely on place coding Complex tones depending on complex combinations of place and frequency coding! Perceiving Sources Auditory Localization: Locating the source of a sound in space Ears being set apart in humans help auditory localization Two cues are particularly important: Sound intensity (loudness) Timing of sounds arriving at each ear Inability to Hear 1 in 1000 people is deaf Many others have hearing deficits. Several causes of deafness; some genetic, others derive from disease, injury, or exposure to loud noise Inability to Hear Two major types of deafness are conductive deafness and nerve deafness Noise-induced hearing loss is a big problem in our society Some age-related hearing loss is normal Effects of Music Brains of musicians are identifiable in that they have larger motor, auditory, and visuospatial areas of the cerebellum than the brains of non-musicians (Sacks, 2007) Links between music training and some language abilities (Patel & Iversen, 2007) Been suggested that music can enhance our spatial abilities (Mozart Effect) (Rauscher, Shaw, & Ky, 1993) The Gustatory System Sense of Taste The Gustatory System The Gustatory System: Sensory system for taste Stimuli are soluble chemical substances Gustatory receptors are clusters of taste cells found in the taste buds that line the trenches around tiny bumps on the tongue The Gustatory System Fifth taste? Umami Perception of Taste Perception of taste quality depends on complex patterns of neural activity Activity initiated by taste receptors Basic taste preferences may be innate Automatically regulated by physiological mechanisms However, most taste preferences are learned Perception of Taste Not everyone has the same ability to taste Non-tasters vs. Supertasters vs. medium tasters Variations in sensitivity mean that when two people taste the same food, they will not necessarily have the same sensory experience Perception of Taste Taste sensitivity influences people’s eating habits Supertasters generally have better health habits than non-tasters! Women more likely to be supertasters than men Perception of Flavour Flavour is a combination of taste, smell, and the tactile sensation of food in one’s mouth Odours very important to perception of flavour The Olfactory System Sense of Smell The Olfactory System Humans are relatively insensitive to smell Stimuli are volatile chemical substances Easily evaporated at room temperature Receptors are olfactory cilia Hair-like structures located in the upper portion of the nasal passages THE OLFACTORY SYSTEM The Olfactory System Buck & Axel (1991) clarified the mechanisms involved in odour recognition A gene set consisting of 1000 different genes affecting operation of olfactory receptor cells Won the Nobel Prize in 2004 for their work! The Olfactory System Odours cannot be classified as neatly as tastes Humans have about 350 different types of olfactory receptors Humans can distinguish among about 10,000 different odours The Olfactory System Sense of smell shows sensory adaptation Perceived strength of an odour usually fades to less than half its original strength within four min Females tend to be somewhat more accurate than males on odour recognition tasks Chemical Communication Pheromones: Chemical messages, typically imperceptible, that can be sent by one organism and received by another member of the same species Humans give off, and are susceptible to, other humans’ pheromones e.g., Stern & McClintock (1998) The Tactile System Sense of Touch The Tactile System Physical stimuli for touch are mechanical, thermal, and chemical energy that affect the skin Can produce perceptions of tactile stimulation (the pressure of touch against the skin), warmth, cold, and pain Human skin has at least six (6) types of sensory receptors The Tactile System Tactile localization is very accurate Nerve cells that carry information about tactile stimulation are routed through the spinal cord to the brainstem Tactile pathway then projects through the thalamus onto the somatosensory cortex Perceiving Pressure Tactile localization is very accurate Nerve cells carry information about tactile stimulation through the spinal cord to the brainstem, then project through the thalamus onto the somatosensory cortex Sensory adaptation also occurs with our perception of pressure  Perceiving Pain Perception of pain can be influenced greatly by expectations, personality, mood, and other factors involving higher mental processes: e.g., placebo effect (Benedetti, 2008) e.g., culture (Jordan, 1983) e.g., contextual factors (Master et al., 2009; Roy et al., 2009; Wegner, 2008) Attention and pain perception interact!  Blocking Pain Gate Control Theory (Melzack & Wall, 1965) Holds that incoming pain sensations must pass through a “gate” in the spinal cord that can be closed, thus blocking ascending pain signals Gate is NOT an anatomical structure, but a pattern of neural activity Blocking Pain Endorphins and serotonin seem to modulate pain perception’ Endorphin = endogenous, or internally produced morphines The Kinesthetic & Vestibular Systems Sense of Position The Vestibular System Kinesthetic System: Monitors the positions of the various parts of the body Most kinesthetic stimulation is transmitted to the brain along the same pathway as tactile stimulation The Vestibular System Vestibular System: Responds to gravity and keeps you informed of your body’s location in space Shares space in the inner ear with the auditory system Semicircular canals make up the largest part of the vestibular system Critical for keeping you oriented and balanced in space! The Visual System Sense of Sight The Visual System The Visual System: Sensory system for sight The stimulus is light A form of electromagnetic radiation that travels as a wave Light Light waves vary in: Amplitude: Affects perception of brightness Wavelength: Affects perception of colour What humans see also varies in purity Influences perception of the saturation, or richness, of colours Visible Light Spectrum THE HUMAN EYE  The Eye Eyes channel light to the neural tissue that receives it, called the retina Light enters through the cornea and then passes through the lens Lens is capable of adjustments – called accommodations When you focus on a close object the lens of your eye gets fatter (rounder) to give you a clear image When you focus on distant objects, the lens flattens out to give you a better image of objects The Eye The eye can make adjustments to alter the amount of light reaching the retina: Iris: Coloured ring of muscle around the pupil Regulates the size of the pupil Pupil: The black centre of the eye; in the centre of the iris Regulates the amount of light passing into the rear chamber of the eye The Retina Retina: The neural tissue lining the inside back surface of the eye Absorbs light, processes images, and sends visual information to the brain Visual Receptors Cones: Specialized visual receptors that play a key role in daylight vision and colour vision Concentrated most heavily in the centre of the retina, and fall off in density toward the periphery Fovea: Tiny spot in the centre of the retina that contains only cones Visual acuity is greatest at this spot Visual Receptors Rods: Specialized visual receptors that play a key role in night vision and peripheral vision Density is greatest just outside the fovea, and gradually decreases toward the periphery of the retina Visual Receptors Adaptation Dark Adaptation: The process in which the eyes become more sensitive to light in low illumination Dark adaptation is complete in ~30min Most adaptation happens in first 10min Seeing Colour All three (3) properties of light influence the perception of colour: 1. Wavelength → hue 2. Amplitude → brightness (value) 3. Purity → saturation Colour Mixture Additive colour mixing: Superimposes lights, putting more light in the mixture than exists in any one light by itself Subtractive colour mixing: Removes some wavelengths of light, leaving less light than was originally there Colour Mixture Additive colour mixing Subtractive colour mixing Trichromatic Theory The human eye has three (3) types of receptors with differing sensitivities to different light wavelengths Eye has specialized receptors sensitive to the specific wavelengths of red, green, and blue All colours are created by an additive mixing process Trichromatic Theory Explains colour blindness Most people who are colour blind are dichromats Three types: red, green, or blue insensitive dichromatism Colour Blindness A red/green colour blind person will confuse a blue and a purple because they can’t ‘see’ the red element of the colour purple http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/ Opponent-Process Theory The human eye has three (3) types of receptors with differing sensitivities to different light wavelengths Each cone is responsive to two (2) wavelengths: Red or Green Blue or Yellow Black or White Opponent-Process Theory Explains afterimages Visual image that persists after a stimulus is removed Dual-Process Theory Combines trichromatic and opponent-process theories Three types of cones & each type sensitive to different wavelengths Depth Perception Depth Perception: Interpretation of visual cues that indicate how near or far away objects are Cues can be monocular or binocular! Depth Perception Monocular depth cues: Based on the image in either eye, alone Motion parallax: Relative motion of objects across the retina Pictorial depth cues: Linear perspective, texture gradients, interposition, relative size, height in plane, light and shadow  Depth Perception Binocular depth cues: Based on the differing views from two eyes Retinal Disparity: Objects project images to slightly different locations on the right and left retinas Right and left eyes see slightly different views Convergence: Sense the eyes converging toward each other as they focus on closer objects Cognition and Vision Let’s put it all together! Bottom-up Processing Emphasizes the stimulus characteristics that are important when you recognize an object (1) Start with the individual elements that make up an object, (2) put them together, and (3) interpret the object as a whole Top-down Processing Interpret sensory information in light of existing knowledge, concepts, & ideas Contextual factors and their related expectations can affect speed of object recognition Especially strong when a stimulus is registered for just a fraction of a second and when stimuli are incomplete or ambiguous Gestalt Psychology Humans have basic tendencies to actively organize what they see For human perception, the whole is greater than the sum of its parts Top-down processing A Gestalt: Has an overall quality that transcends the individual elements Gestalt Psychology Figure-ground relationship Organize scenes to a central figure (focus) and a background Humans are good at focusing on figures! Gestalt psychology Ambiguous figure-ground relationships Gestalt Reversals Bottom-up: The neurons in the visual cortex become adapted to one figure, so you are more likely to see the alternative Top-down: People actively try to solve the visual paradox by switching between the two reasonable solutions Illusory Contours You can ‘see’ boundaries that do not exist! Gestalt Laws of Organization (4): 1. Law of Similarity 2. Law of Proximity 3. Law of Closure 4. Law of Continuity Perceptual Constancies Size Constancy Illusions Perceptual constancies show that context can produce illusions e.g., converging lines disrupt size constancy MULLER-LYER ILLUSION  Illusions Monocular depth cues are manipulated to produce an impossible triangle, a never-ending staircase, and the “devil’s tuning fork.” Experience & Perception