Chapter 4 Sensation

Basic Principles of Sensation Sensation is the process that detects stimulation from our bodies and our environment.

Basic Principles of Sensation Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.

Basic Principles of Sensation Psychophysics is the study of how physical stimuli are translated into psychological experience.

Physical Properties of Waves Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Great amplitude (bright colors, loud sounds) Small amplitude (dull colors, soft sounds)

Color and Wavelength of Light An object appears as a particular color because it absorbs certain wavelengths of light and reflects others. These wavelengths are simply energy; colors are created by our nervous system in response to them. Species differ in what they see when looking at the same object. Our difference threshold for colors is so low that the average person can discriminate about 2 million different colors.

Sensory Information Must Be Converted into Neural Impulses Sound, light, etc. cannot travel through our nerves to the brain. Sensory organs convert their physical properties into neural impulses. This conversion process is called transduction.

Sensory Information Must Be Converted into Neural Impulses Transduction takes place at sensory receptors. Next, connecting neurons in the sense organs send this information to the brain. The brain processes these neural impulses into what we experience. Some stimuli are just as real as those that we can transduce, but they are not a part of our sensory experience.

Sensation Sensory receptors: specialized forms of neurons; the cells that make up the nervous system LO 3.1 Sensation and How It Enters the Central Nervous System

Sensation Sense Organs: eyes ears nose skin taste buds LO 3.1 Sensation and How It Enters the Central Nervous System

Our Senses Vary in Their Sensitivity Thresholds Signal-detection theory contends that detection of a stimulus is influenced by observers’ expectations. How likely is the stimulus to occur? How important or rewarding is detecting it? So absolute threshold may vary. It is usually defined as the intensity of a stimulus that can be detected 50% of the time.

Our Senses Vary in Their Sensitivity Thresholds Absolute threshold: the lowest level of intensity of a given stimulus that a person can detect half the time As people age, their absolute thresholds for all senses increase.

Sensation--Thresholds When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal” LowAbsolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli

Subliminal stimuli Subliminal stimuli: stimuli that are below the level of conscious awareness just strong enough to activate the sensory receptors, but not strong enough for people to be consciously aware of them limin: “threshold” sublimin: “below the threshold” supraliminal: “above the threshold”

Our Senses Vary in Their Sensitivity Thresholds Difference threshold is the smallest difference between two stimuli that is detected half (50%) of the time. It is also called the “just-noticeable difference” or jnd.

Our Sensory Receptors Adapt to Unchanging Stimuli Sensory adaptation: the tendency for our sensory receptors to have decreasing responsiveness to stimuli that continue without change. Auditory adaptation occurs much more slowly than adaptation to odors, tastes, and skin sensations.

Habituation and Sensory Adaptation Habituation: the tendency of the brain to stop attending to constant, unchanging information Sensory adaptation: the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging LO 3.1 Sensation and How It Enters the Central Nervous System

Habituation and Sensory Adaptation Microsaccades: constant movement of the eyes; tiny little vibrations that people do not notice consciously; prevents sensory adaptation to visual stimuli LO 3.1 Sensation and How It Enters the Central Nervous System

Sensory Adaptation

Vision

We See Only a Narrow Band of Electromagnetic Radiation Wavelengths of visible light range from 400 to 750 nanometers. Shorter wavelengths are experienced as violet. Intermediate ones as blue, green, and yellow. Longer ones as red. Other forms of electromagnetic energy that our eyes cannot detect are: Radio Infrared Ultraviolet X-ray radiation

Vision Spectrum of Electromagnetic Energy

Major Structures of the Human Eye

Structure of the Eye Retina: final stop for light in the eye contains three layers: ganglion cells bipolar cells photoreceptors that respond to various light waves LO 3.2 What Is Light?

Structure of the Eye Rods: visual sensory receptors found at the back of the retina; responsible for noncolor sensitivity to low levels of light Cones: visual sensory receptors found at the back of the retina; responsible for color vision and sharpness of vision LO 3.2 What Is Light?

Photoreceptors in the Retina Rods (125 million) Located at the edges of the retina. Are not involved in color vision. Function best under low-light conditions. Cones (7 million) Located near the center of the retina (the fovea). Require bright light to be activated. Play a key role in color vision.

Vision--Receptors Receptors in the Human Eye ConesRods Number Location in retina Sensitivity in dim light Color sensitive?Yes Low Center 6 million No High Periphery 120 million

Structure of the Eye Blind spot: area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve; insensitive to light LO 3.2 What Is Light?

Retina’s Reaction to Light

Audition (Hearing)

Sound Is the Stimulus for Hearing Soundwaves (pressure) are created when an object vibrates. Wave speed or frequency corresponds to pitch. Amplitude (wave height) corresponds to loudness of a sound. Most sounds are a combination of many different waves of different frequencies. This sound complexity is caled timbre.

Auditory System: Three major parts of the Ear Outer ear: The pinna is the most visible part of the outer ear. The auditory canal is funnel shaped. The eardrum is at the end of the auditory canal and it vibrates in sequence with sound waves.

Audition- The Ear

Auditory System: Three major parts of the Ear Middle ear: The ossicles are three tiny interconnected bones—the hammer, anvil, and stirrup —that move and amplify sound waves before sending them to the inner ear.

Auditory System: Three major parts of the Ear Inner Ear innermost part of ear, containing the cochlea, semicircular canals and vestibular sacs Cochlea coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

Sound Localization Sound localization: the ability to locate objects in space solely on the basis of the sounds they make Because the ears are only 6 inches apart, the time lag between the sound reaching both ears is very short. Even such small time lags provide the auditory system with sufficient information to locate the sound.

Soundwaves Sound Waves and Decibels A typical sound wave. The higher the wave, the louder the sound; the lower the wave, the softer the sound. If the waves are close together in time (high frequency), the pitch will be perceived as a high pitch. Waves that are farther apart (low frequency) will be perceived as having a lower pitch.

Soundwaves

Sound Waves and Decibels A decibel is a unit of measure for loudness. See the next two slides for decibels of various stimuli.

The Intensity of Some Common Sounds

Smell and Taste: The Chemical Senses Olfaction: the sense of smell The stimuli are airborne molecules Olfactory receptor cells are at the top of the nasal cavity. These cells transmit information to the olfactory bulb at the base of the brain. The olfactory bulb processes this information and sends it to the primary olfactory cortex.

Smell (Olfaction) Olfaction (Olfactory Sense) sense of smell Olfactory Bulbs areas of the brain located just above the sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells There are at least 1,000 olfactory receptors. LO 3.6 How Work

The Olfactory Receptors A cross section of the nose and mouth. This drawing shows the nerve fibers inside the nasal cavity that carry information about smell directly to the olfactory bulb just under the frontal lobe of the brain (shown in green).

The Olfactory Receptors (b) A diagram of the cells in the nose that process smell. The olfactory bulb is on top. Notice the cilia, tiny hairlike cells that project into the nasal cavity. These are the receptors for the sense of smell.

Smell (Olfaction)

Olfaction Olfactory sensitivity is determined by the number of receptors in the epithelium. Odors can evoke memories and feelings associated with past events.

Gustation: the sense of taste Gustation occurs when a substance makes contact with special receptor cells in the mouth, called taste buds. Most taste buds are located on the tongue, but some are in the throat and on the roof of the mouth.

Taste Taste buds taste receptor cells in mouth; responsible for sense of taste Gustation the sensation of a taste LO 3.6 How Senses of Taste and SmellWorkLO 3.6 How Senses of Taste and SmellWork

The right side of this drawing shows the nerves in the tongue’s deep tissue. The right

The right side of this drawing shows the nerves in the tongue’s deep tissue.

Microphotograph of the surface of the tongue, showing two different sizes of papillae. The taste buds are located under the surface of the larger red papillae, whereas the smaller and more numerous papillae form a touch- sensitive rough surface that helps in chewing and moving food around the mouth.

Taste Five Basic Tastes: sweet sour salty bitter “brothy,” or umami LO 3.6 How Senses of Taste and Smell Work

Gustation: the sense of taste When taste cells absorb chemicals dissolved in saliva, they trigger neural impulses, transmitted to one of two brain areas: First: information first sent to the thalamus and then to the primary gustatory cortex, where taste identification occurs Second: information sent to the limbic system, which allows a quick response to a taste prior to conscious identification of it (example, spitting out sour milk)

The Five Primary Tastes Not all researchers agree on this.

Somasthetic (Bodily) Senses

The Skin Senses Pressure, Temperature, & Pain Our skin is our largest sensory organ. Sense of touch is actually a combination of three skin senses: Pressure: physical pressure on the skin Temperature: The skin contains two kinds of temperature receptors, one sensitive to warm and the other to cold.

Pain: The Body’s Warning System Pain is induced through tissue damage or intense stimulation of sensory receptors. Gate-control theory proposes that small-diameter nerve fibers (S-fibers) and large-diameter nerve fibers (L- fibers) open and close “gateways” for pain in the spinal cord.  Pain gateways can be closed—thus preventing pain messages from reaching the brain—by a class of substances known as endorphins.

Cross Section of the Skin and Its Receptors The skin is composed of several types of cells that process pain, pressure, and temperature. Some of these cells are wrapped around the ends of the hairs on the skin and are sensitive to touch on the hair itself, whereas others are located near the surface, and still others just under the top layer of tissue.

Somasthetic Senses Vestibular senses: the sensations of movement, balance, and body position; provide information on the position of the body in space by sensing gravity and motion (inner ear). Sensory conflict theory: an explanation of motion sickness in which the information from the eyes conflicts with the information from the vestibular senses, resulting in dizziness, nausea, and other physical discomforts LO 3.7 Sense of Touch, Pain, Motion, and Balance

The Proprioceptive Senses: Body Movement and Location Kinesthetic sense: provides information about the movement and location of body parts with respect to one another This information comes from proprioceptors (receptors in muscles, joints, and ligaments.)