Definitions Sensation Perception chapter 6 Definitions Sensation The detection of physical energy emitted or reflected by physical objects Occurs when energy in the external environment or the body stimulates receptors in the sense organs Perception The process by which the brain organizes and interprets sensory information Lets start off with some simple definitions so we all understand what we are talking about. Sensation is the detection of physical energy emitted or reflected by objects. Each sense detects a different type of energy, which we’ll talk about more in a few minutes. A sensation occurs when this energy stimulates the appropriate receptor in a sense organ. Perception is the process by which the brain organizes and interprets all of this sensory information.

Sensation and perception chapter 6 Sensation and perception

Sensation What are the sensory systems? Sight, sounds, touch, pain, smell, taste, sensation of movement Why are the sensory systems important? Perception of external world Maintains arousal, forms body image, regulates movement Basis for our knowledge about the world and our surroundings.

Psychophysics Correlates quantitative aspects of physical stimuli (energy) with the sensations they evoke 4 elementary attributes: Modality Intensity Duration Location

Attributes of Sensation: Modality Quality of a sensation Different forms of energy = Different sensations 5 major: vision, hearing, touch, taste, smell Submodalities: Touch – sweet, salty, bitter, sour Vision – color, movement Law of Specific Energies 1826 Johannes Muller Each modality = activated by a specific stimulus = different sensory nerve fiber Sensory receptors are maximally sensitive to a specific energy

Modality Stimulus Receptor Types Receptor (energy) Vision Light Photoreceptor Rods, Cones Audition (hearing) Sound Mechanoreceptor Hair cells (cochlear) Balance Head motion Hair cells (semicircular canals) Somatic (touch) Mechanical, thermal, noxious (chemical) Mechanoreceptor, thermoreceptor, nociceptor, chemoreceptor Dorsal root ganglion neurons Taste Chemical Chemoreceptor Taste buds Smell Olfactory sensory neurons You may be asking yourself, what does she mean by energy. Well here are the different modalities and these are the stimuli or energy that activates them. Each has a specific type of receptor, which allows this specificity, as well as a specific location of receptors that sends projections to a specific bundle of nerves just as Muller hypothesized in 1826. Adapted from Kandel, Schwartz, and Jessel, 1991

Attributes of Sensation: Intensity Strength of Energy  Amount of sensation Frequency of action potentials strong stimulus = more action potentials fired # of fibers activated strong stimulus = more fiber stimulated Absolute Threshold Smallest amount of energy/stimulation that can reliably be detected Variable Influenced by practice, fatigue, context The intensity of a stimulus or the amount of sensation is determined by the strength of the sensation. It helps us to distinguish stimuli that differ in intensity and stimuli that are stronger or weaker than one another. Every stimuli has an absolute threshold, which is the smallest amount of energy or stimulation that can reliably be detected. Now b/c this detection is variable and can be influenced by practice, fatigue or the context, the absolute threshold is determined by the smallest amount of energy that is detected by someone 50% of the time.

Absolute thresholds Vision Hearing Smell Touch Taste chapter 6 Absolute thresholds Vision A single candle flame from 30 miles on a clear night Hearing The tick of a watch from 20 feet in total quiet Smell One drop of perfume in a 6-room apartment Touch The wing of a bee on the cheek, dropped from 1 cm Taste One teaspoon of sugar in 2 gallons of water Here are some reported absolute thresholds for the different modalities.

Attributes of Sensation: Intensity Strength of Energy  Amount of sensation Frequency of action potentials strong stimulus = more action potentials fired # of fibers activated strong stimulus = more fiber stimulated Absolute Threshold Smallest amount of energy/stimulation that can reliably be detected Variable Influenced by practice, fatigue, context Difference Threshold Smallest difference that can be detected when 2 stimuli are compared Just Noticeable Difference (JND)

Signal-detection theory chapter 6 Signal-detection theory A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process and quantifies the ability to distinguish between the stimuli and noise

Drugs – Mechanism of Action on the sensation of pain Drugs that elevate the pain threshold Morphine Reduces detectibility of painful stimuli = raises threshold Elevates criterion used to determine if a stimuli is painful = creates noise Marijuana Elevates criterion used to determine if stimuli is painful = makes noise

Attributes of Sensation: Duration Stimulus intensity and Perceived Intensity Adaptation The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious Prevents us from having to respond continuously to unimportant information Deprivation The absence of normal levels of sensory stimulation

Attributes of Sensation: Location Spatial aspects of sensation: Ability to locate origin of sensation Ability to distinguish 2 closely spaced stimuli Two-Point Threshold Minimum distance between 2 stimuli that allows them to be perceived as distinct Function of receptive field of receptor and sensory neurons

Commonalities of the Senses All extract same basic information Modality, intensity, duration, location Similar organization Sensory receptors for specific type of energy Receptor transforms energy into electrochemical signal  action potentials Travel up afferent fibers to the brain Relay information to Thalamus (except smell) Continue on to specific regions in cortex

Vision Stimuli (energy) = light waves chapter 6 Vision Stimuli (energy) = light waves 3 Psychological Aspects of Vision: Hue Related to the wavelength of light Brightness Related to the amount of light emitted from or reflected by an object – amplitude of wavelength Saturation Related to the complexity of light waves - # of different wavelengths

Vision Adapted from Univ. Virginia, Dept of Astronomy

chapter 6 What we see

Anatomy of the Eye Cornea Lens Iris Pupil chapter 6 Anatomy of the Eye Cornea Protects eye and bends light toward lens Lens Focuses on objects by changing shape Iris Controls amount of light that gets into eye Pupil Aperture through which light reaches the retina

Rods and Cones Retina Rods Cones chapter 6 Rods and Cones Retina Neural tissue lining the back of the eyeball’s interior containing the receptors for vision Rods Visual receptors that respond to dim light Cones Visual receptors involved in color vision

chapter 6 Rods and Cones

Structures of the retina chapter 6 Structures of the retina

chapter 6 Your turn You have a hard time locating your red car at night, in the poorly lit mall parking lot. Why? 1. Your rods are less sensitive to color in dim light. 2. Your cones, which detect color, do not function well in dim light. 3. Your ganglion cells receive insufficient overall stimulation to function. 4. Your rods, which detect color, do not function well in dim light.

The visual system is not a camera chapter 6 The visual system is not a camera Visual processing is done in the brain The visual image that was reflected onto our retina is broken up into simple and complex features that the brain perceives, processes and interprets Simple features - light and dark spots - Ganglion cells and neurons in Thalamus Complex features – Lines with specific orientations, bulls-eyes, spirals, faces) - Feature-detector cells in the Visual cortex - Sensitive to specific features in the environment

chapter 6 Visual Cortex Neurons: Feature-Detector Cells Respond to lines oriented in a particular direction and in a particular space in the visual field Hubel & Wiesel Experiment

Hubel and Wiesel’s experiment chapter 6 Hubel and Wiesel’s experiment Simple Cell in Visual Cortex Hubel DH Sci Amer 209:54-62,1963

How do we see color? Two theories: Trichromatic theory Opponent-process theory

Trichromatic theory Young-Helmholtz Theory: chapter 6 Trichromatic theory Young-Helmholtz Theory: The eye detects 3 primary colors Red, blue, and green Retina has 3 basic cones detects the 3 primary colors All other colors detected by the combined activity of these 3 cones

Opponent-process theory chapter 6 Opponent-process theory The visual system treats pairs of colors as opposing or antagonistic 3 opponent channels Red-Green Blue-Yellow Black-White If opponent-process cells are inhibited by a color then removal of the color results in a burst of activity Many respond in the opposite fashion to red and green, i.e. fire in response to red and turn off in response to green Negative afterimage

Form Perception: Gestalt principles chapter 6 Form Perception: Gestalt principles Proximity Things close to one another are grouped together Closure The brain tends to fill in gaps to perceive complete forms

Form Perception: Gestalt principles cont. chapter 6 Form Perception: Gestalt principles cont. Similarity Things that are alike are perceived together Continuity Seeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction.

chapter 6 Your turn Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram? 1. Similarity 2. Proximity 3. Closure 4. Continuity

Depth and distance perception chapter 6 Depth and distance perception Binocular cues Require both eyes working together Convergence Turning inward of the eyes, which occurs when they focus on a nearby object Retinal disparity The slight difference in lateral separation between two objects as seen by the right and left eyes

Depth and distance perception chapter 6 Depth and distance perception Monocular cues For objects over 50 feet away Does not depend on both eyes Interposition Linear Perspective Light and Shadow Motion Parallax Relative Size Relative Clarity Texture Gradients

chapter 6 Visual constancies The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce Shape constancy Location constancy Size constancy Brightness constancy Color constancy

Last Class in Review Sensation Perception Vision The detection of physical energy emitted or reflected by physical objects Perception The process by which the brain organizes and interprets sensory information Psychophysics – attributes of sensation Modality, Intensity, Duration, Location Law of Specific Energies Absolute Threshold vs. Difference Threshold (JND) Adaption and Deprivation Two-Point Threshold Vision Psychological Attributes – hue, brightness, saturation Anatomy – visual receptors = rods and cones; feature detector cells Depth and Distance perceptions: monocular and binocular cues Gestalt Principles: proximity, closure, similarity, continuity

Sensation and Perception chapter 6 Sensation and Perception Learning Objectives: What are the 3 main psychological dimensions of hearing? What are the major structures of the inner ear that contribute to the sense of hearing? Understand how the Gestalt principles may apply to other sensations, such as hearing. What are the 5 major tastes? Why do people tastes things differently? What are the basic senses of the skin? How is sensation organized? (hint: understand somatotopy) How does gate-control theory account for our perception of pain? Is there any evidence that some perceptual abilities are present from birth? What are these abilities and what is the evidence? What 5 factors can influence our perception?

What we hear (audition) chapter 6 What we hear (audition) Stimulus (energy) = wave of pressure caused by vibrations 3 Psychological Aspects of Sound: Pitch Frequency of a pressure wave Measured in hertz (Hz) Loudness Intensity (amplitude) of a pressure wave Measured in decibels (dB) Timbre Complexity of a pressure wave White noise – all frequencies of the sound spectrum

Psychological Aspects of Sound From Genetic Science Learning Center, University of Utah, http://gslc.genetics.utah.edu. Example of differences in pitch and complexity

chapter 6 Anatomy of the Ear

Gestalt Principles in Audition Proximity Which sounds go together to form words Continuity Helps you follow 1 persons voice in a room full of background noise Similarity Might also help you follow 1 persons voice in a room full of background noise Closure Helps you complete words when the speakers voice trails off

Auditory localization chapter 6 Auditory localization Sounds from different directions are not identical as they arrive at left and right ears. Loudness Timing Phase The brain calculates a sound’s location by using these differences.

Taste (Gustation) Taste buds = Bundles of taste receptor cells chapter 6 Taste (Gustation) Taste buds = Bundles of taste receptor cells Taste hairs (microvilli) contain taste receptors Taste stimuli (energy) = chemical Taste receptor cells send signals to sensory nerves (taste nerves) Sensory nerves send action potential to the brain

Five tastes Five basic tastes Why do people have different tastes? chapter 6 Five tastes Five basic tastes Salty – keeps electrolytes (salt-balance) in check Sour – detects acidity = rancid food Bitter – allows sensing of natural poisons Sweet – energy rich nutrients, presence of sugars Umami – taste of amino acids (glutamate) = protein rich foods Why do people have different tastes? Genetics - supertasters Culture Learning Food attractiveness

Smell (Olfaction) Smell stimuli (energy) = chemicals chapter 6 Smell (Olfaction) Smell stimuli (energy) = chemicals Enter through the nose or mouth and pass into nasal cavity. Receptors  Olfactory nerve  Olfactory bulb  Pyriform cortex, hypothalamus, thalamus, frontal cortex, hippocampus

Senses of the Skin Basic skin senses: Tactition (touch) - stimuli is pressure mechanoreceptor Thermoception (hot & cold) stimuli is thermal thermoreceptor Nociception (pain) stimuli is noxious nociceptor

chapter 6 Sensitivity to touch

Somatotopy Adapted from Sabes Lab - UCSF

The environment within chapter 6 The environment within Kinesthesis The sense of body position and movement of body parts Equilibrium The sense of balance - Semicircular canals Sense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head

chapter 6 Critical period An important period of time during development when the brain is capable of acquiring a specific ability Environmental stimulation needed to strengthen hard-wired innate connections If infants miss out on experiences during a crucial period of time, perception will be impaired. Zebra finches learn their adult song from a tutor during a critical period