Sensation
Ψ 100/101 Nov 4 ‘09
True/False 1.
On a clear, dark night most of us can see a candle flame close to 50 kilometres away.
2.
Advertisers are able to shape our buying habits through subliminal messages.
3.
Constant eye movements prevent our vision from being seriously disrupted.
4.
The retina of the eye is actually brain tissue that migrates to the eye during early fatal development.
5.
If we stare at a green square for a while and then look at a white sheet of paper, we see red.
6.
People who live in noisy environments are more likely to suffer from high blood pressure, anxiety, and feelings of helplessness.
7.
Blind musicians are more likely than sighted ones to develop perfect pitch.
8.
Touching adjacent cold and pressure spots triggers a sense of wetness.
9.
People who are born without the ability to feel pain usually die by early adulthood.
10. Without their smells, a cold cup of coffee may be hard to distinguish from a glass of red wine. 2
Chapter Objectives Contrast sensation and perception, and explain the difference between bottom-up and top-down processing. Contrast sensation and perception, and explain the difference between bottom-up and top-down processing. Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute threshold and be influenced by them. Describe sensory adaptation, and explain how we benefit from being unaware of unchanging stimuli. Define transduction, and specify the form of energy our visual system converts into the neural messages our brain can interpret. Describe the major structures of the eye, and explain how they guide an incoming ray of light toward the eye’s receptor cells. Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light. Discuss the different levels of processing of visual information travelling from the eye’s retina to the brain’s cortex. Define parallel processing, and discuss its role in visual information processing.
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Chapter Objectives Cnt Explain how the Young-Helmholtz and opponent-process theories of color vision. Explain the importance of color constancy. Describe the pressure waves we experience as sound. Describe the three regions of the ear, and outline the series of events that triggers the electrical impulses sent to the brain. Contrast place and frequency theories, and explain how they help us to understand pitch perception. Describe how we pinpoint sounds. Contrast the two types of hearing loss, and describe some of their causes. Describe how cochlear implants function, and explain why Deaf culture advocates object to these devices. Describe the sense of touch. State the purpose of pain, and describe the bio-psychosocial approach to pain. Describe the sense of taste, and explain the principle of sensory interaction. Describe the sense of smell, and explain why specific odors so easily trigger memories. Distinguish between kinesthesis and the vestibular sense.
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Overview Psychophysics Sensory Adaptation The Eye & Vision The Ear & Hearing Other senses Touch Taste Smell Body position & Internal Senses
Sensation vs Perception Sensation: the process of detecting physical energy (a stimulus) from the environment and converting it into neural signals Perception: the process by which we select, organize, and interpret our sensations
Interactive Processing Bottom-up Processing: Analysis of the stimulus that begins with the sense receptors and works up to the level of the brain and mind Top-down Processing: Information processing that is guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations Interactive Processing: The combination of bottom-up and top-down processing
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Psychophysics The study of how physical stimuli (sensations) are translated into psychological experiences (perceptions) The goal of psychophysics is to provide a quantitative description of the relationship between the intensity of sensations and perceptions One of the oldest topics in psychology … part of the foundation of psychology as a discipline
Thresholds Absolute threshold … a dividing line between what (signal) has detectable energy and what signal does not Difference threshold … the minimum amount of stimulus intensity change required to produce a noticeable (perceptible) change (JND: just noticeable difference)
Signal Detection Theory
Signal Detection Theory SDT is useful for computing how and when we detect the presence of a faint stimulus (signal) amid background noise (or other stimulation) SDT assumes that there is no single absolute threshold and detection depends on Person’s experience Expectations Motivation Level of fatigue
Proportion of “Yes” Responses 0.00 0.50 1.00
Method: Absolute Threshold
0 5 10 15 20 25 Stimulus Intensity (lumens)
Difference Threshold The minimum difference between two stimuli required for detection 50% of the time Also called just the noticeable difference (JND)
Method: Difference Threshold On each trial, present 1 base stimulus plus one comparison stimulus Use different base stimuli on different trials Comparison stimulus differs from base by some amount Subject’s task: On each trial, decide whether the two stimuli are the same or different Difference Threshold: The minimum difference between two stimuli that a subject can detect 50% of the time
Weber’s Law Weber’s Law … to perceive a difference b/w 2 stimuli, the 2 stimuli must differ by a constant %, not by a constant amount The increase in a stimulus needed to produce a JND is defined as dR = C * R dR = difference in stimulus R needed for detection or perception C = constant (e.g., .10) R = Intensity of original (starting stimulus)
Weber’s Law: Example In order to hear an increase in a tone played at 50 decibels, the comparison stimulus has to have 55 decibels dR = .10 * 50 = 5
Therefore, if the standard tone were to have 100 decibels, a comparison stimulus would be noticed as louder only if it had 110 decibels dR = .10 * 100 = 10
Weber’s Law: Example If a $5.00 per hour worker requires a 50 cent raise to notice the difference, a $10 per hour worker may need to receive a _____raise to notice? Weber’s Law: Findings
Stimulus
Constant (k)
Light
8%
Weight
2%
Tone
0.3%
Subliminal Threshold
Refers to stimuli below one’s absolute threshold for conscious awareness
Sensory Adaptation Diminished sensitivity to a stimulus as a consequence of constant stimulation by that stimulus Nerve cells fire less frequently Permits us to perceive what is useful
Sensory Adaptation
Transduction Location of Sense Organ Environmental Stimuli
Energy Transduced
Eye
Light
Radiant Energy
Ear
Sound
Mechanical Energy
Vestibular System
Tilt and Rotation
Mechanical Energy
Tongue
Taste
Recognition of Molecular Shape
Nose
Odour
Recognition of Molecular Shape
Touch
Mechanical Energy
Skin, Internal Organs
Muscle
Temperature
Thermal Energy
Vibration
Mechanical Energy
Pain
Chemical Reaction
Stretch
Mechanical Energy
Light/Electromagnetic Energy
Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next.
Intensity (Brightness) Intensity is the amount of energy in a wave determined by the amplitude. It is related to perceived brightness.
The Eye
Accommodation Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.
Acuity of Vision
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Retina
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Distribution of Rods & Cones
Test your Blind Spot Close your left eye, and fixate your right eye on the black dot. Move toward and away from the slide. At some point, the car on the right will disappear due to a blind spot.
Transduction of Light by Photoreceptors
The Eye and Its Functions
Feature Detection
Ross Kinnaird/ Allsport/ Getty Images
Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement.
Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.
From Sensation to Recognition
Theories of Color Vision Trichromatic Theory: Helmholtz suggested that the retina should contain three receptors that are sensitive to red, blue and green colors. Opponent Process Theory: Hering proposed that we process four primary colours combined in pairs of red‐green, blue‐yellow, and black‐white.
Opponent Process Theory
Colours Subtraction of Colours If three primary colours (pigments) are mixed, subtraction of all wavelengths occurs and the colour black is the result. Addition of Colours If three primary colours (lights) are mixed, the wavelengths are added and the colour white is the result.
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Opponent Colours
Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report whether or not you see Canada’s flag. 44
Colour Blindness Genetic disorder in which people are blind to some colors. Protanopia: Red cones filled with green photopigment Deuteranopia: Green cones filled with red photopigment Tritanopia: Lack of blue cones
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Ishihara Color Vision Test
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Audition Sound waves are composed of compression and rarefaction of air molecules.
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Sound Properties Frequency (pitch): The dimension of frequency determined by the wavelength of sound. Intensity (Loudness): Amount of energy in a wave, determined by the amplitude, relates to the perceived loudness. Timbre: The simplicity/complexity of the wave 48
Sound Properties
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Loudness of Sound
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The Ear
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Cochlea
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Theories of Audition Place Theory suggests that sound frequencies stimulate the basilar membrane at specific places resulting in perceived pitch. Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. 53
Localization of Sounds Because we have two ears, sounds that reach one ear faster than the other ear cause us to localize the sound.
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Hearing Loss Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea. Sensorineural Hearing Loss: Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness. 55
Hearing Deficits Older people tend to hear low frequencies well but suffer hearing loss when listening for high frequencies.
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Deaf Culture Cochlear implants are electronic devices that enable the brain to hear sounds.
Wolfgang Gstottner. (2004) American Scientist, Vol. 92, Number 5. (p. 437)
EG Images/ J.S. Wilson ©
Deaf Musician
Cochlear Implant
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Pain Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain.
AP Photo/ Stephen Morton
Ashley Blocker (right) feels neither pain nor extreme hot or cold.
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Biopsychosocial Influences
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Gate‐Control Theory Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed.
Gary Comer/ PhototakeUSA.com
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Pain Control Pain can be controlled by a number of therapies including, drugs, surgery, acupuncture, exercise, hypnosis, and even thought distraction.
SA Questions What is meant by top-down and bottom-up processing? What is psychophysics? What percentage of visual stimuli are correctly identified at the level of the absolute threshold? What factors are likely to influence an individual’s absolute threshold? What is sensory adaptation and how does it differ from habituation? Explain/state how the wavelength, intensity and purity of a light source affect visual perception. Explain/state how the wavelength, intensity/amplitude and complexity of a sound source affect auditory perception. Explain/state what information we (humans) use for locating the source of a sound. Which of our primary senses (vision, hearing, smell, taste, touch) does not make a direct connection with the thalamus? 62