Sensation & Perception (continued) PDF

Sensation & PS YCH 100 Perception C ARLY D. MI RON, M A (continued) The Visual System  The Visual System: The Stimulus Light is a form of electromagnetic radiation that travels as a wave Amplitude: the distance from the center line of the wave to the...

Sensation & PS YCH 100 Perception C ARLY D. MI RON, M A (continued) The Visual System  The Visual System: The Stimulus Light is a form of electromagnetic radiation that travels as a wave Amplitude: the distance from the center line of the wave to the top point of the crest or the bottom point of the trough - perception of brightness Wavelength: the length of a wave from one peak to the next Frequency: the number of waves that passes in a given time period expressed in terms of hertz(Hz) - perception of color  Perception of Color Wavelength and Color In human, light wavelength is associated with perception of color Different wavelengths of light are associated with our perception of different colors - Longer wavelengths = reds - Intermediate wavelengths = greens - Shorter wavelengths = blues and violets Amplitude and Color The amplitude of light waves is associated with brightness/intensity of color Longer amplitudes appear brighter  The Eye The eye: the major sensory organ involved in visual perception The eye has two main purposes - Providing a “house” for the neural tissue that receives light stimulus, sends signal to the brain - Channeling light toward the retina, a thin layer of tissue that lines the back of the eye on the inside  Anatomy of the Visual System Light waves are transmitted across the cornea and enter through the pupil The light crosses the lens and is focused on the fovea, which is part of the retina The fovea contains photoreceptors (visual receptors) Photoreceptors are connected to retinal ganglion cells. Axons from these cells exit through the back of the eye where they form the optic nerve. The optic nerve then carries the visual information to the brain. Blind spot – a point of no receptors, where information exits the eye, where we cannot respond to visual information.  Photoreceptors: Rods and Cones Cones: Phototopic (daytime) vision Work best in bright light conditions High-acuity color information, spatial resolution Three types of cone cells Located in the fovea Rods: Scotopic (nighttime) vision Work best in low light conditions High-sensitivity to the light stimulus Allows for low-acuity vision in dim light Involved in the perception of movement in our peripheral vision Located in the periphery of the retina  Optic Chasm The optic nerve of each eye merges at the optic chiasm, an X-shaped structure just below the cerebral cortex Information from the right visual field is sent to the left hemisphere and vice versa This information is then sent to the occipital lobe for processing This illustration shows the optic chiasm at the front of the brain and the pathways to the occipital lobe at the back of the brain, where visual sensations are processed into meaningful perceptions.  Theories of Color Vision Trichromatic Theory of Color Vision All colors can be produced by combining red, yellow, and blue Applies to the retina where color vision is controlled by three types of cones Opponent-Process Theory Color is coded in opponent pairs. Black – White Yellow – Blue Green – Red Some cells are excited by one of the opponent colors and inhibited by the other. Applies to cells after the retina **Research has found that both theories are true but for different parts of the visual system.  SUPPORT FOR OPPONENT-PROCESS THEORY When staring at a colored stimulus, the color-pairings of the opponent-process theory lead to a negative afterimage (see the opposite colors after) Afterimage: continuation of a visual sensation after removal of the stimulus Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper. What do you see?  Depth Perception Depth Perception: our ability to perceive spatial relationships in 3D Depth cues of a visual scene are used to establish our sense of depth Binocular cues: cues that rely on use of both eyes; allow us to see depth Binocular/retinal Convergence - disparity - slightly when two eyes different view of look together, the world that inward, on an each eye object receives  Monocular Visual Cues Monocular cues: cue that relies on only one eye Linear Interposition perspective – partial – when two overlap of parallel lines objects seem to (aka converge. occlusion)  Gestalt Principles of Perception Gestalt psychologists believe that organisms perceive entire patterns or figures, not individual elements ‘whole is more than the sum of its parts’  Gestalt Principles Figure-ground relationship The idea that we tend to segment our visual world into figure and ground. Figure: Person or object that is the focus of visual field Ground: the background Our perception can vary depending on what we view as figure and what we view as ground.  Gestalt Principles Proximity The idea that things that are close to one another tend to be grouped together.  Gestalt Principles When looking at this array of dots, we likely perceive four alternating rows of colors. Similarity The idea that things that are alike tend to be grouped together.  Gestalt Principles Continuity The idea that we are more likely to perceive continuous, smooth flowing lines rather than jagged, broken lines. Good continuation would suggest that we are more likely to perceive this as two overlapping lines, rather than four lines meeting in the center.  Gestalt Principles Closure The idea that we organize our perceptions into complete objects rather than as a series of parts. Closure suggests that we will perceive 3 black circles occluded by one white triangle / one complete circle and one complete rectangle rather than a series of segmented lines. Duck or Rabbit? Take a look at the following figure. How might you influence whether people see a duck or a rabbit? Hint: Think about top-down processing  Reading Review Visual Intelligence, Donald Hoffman - Perception as a construction - Visual illusions highlight limitations of our perception - Visual experiences are like computer icons - other shortcuts you identified? In what ways do you think our past experiences and knowledge influence the way we construct our visual experiences? The Auditory System  The Stimulus – Soundwaves Frequency of sound waves = Pitch (highness or lowness of sound) High frequency = high-pitched sound Low frequency = low-pitched sound Sound pitch is measured in hertz (Hz) Amplitude of sound waves = Loudness Higher amplitude = louder sounds Lower amplitude = quieter sounds Loudness is measured in decibels (dB) typical conversation = 60 dB rock concert = 120 dB potential for hearing damage = 80 – 130 dB  Soundwaves Purity of sound A pure sound has a single frequency In most instances, however, sounds are complex mixtures of multiple frequencies resulting in the perceptual sound quality called timbre. Timbre: Tone color or quality Think about the tone of identical loudness and pitch of a violin versus a flute. This is the quality of timbre  Anatomy of the Auditory System The ear is divided into 3 divisions: Outer – pinna, auditory canal and tympanic membrane Middle - the three ossicles: malleus, incus, and stapes Inner - cochlea and basilar membrane Soundwaves  Outer Ear Pinna The visible portion of the outer ear Collects sound waves and channels them into auditory canal Auditory canal (external auditory canal) A pathway running from the outer ear to the middle ear Funneling sound waves toward the tympanic membrane (ear drum) Tympanic membrane (ear drum) Separates the outer ear from the middle ear Sound waves reach the tympanic membrane they cause the vibration which will be transferred to the middle ear.  Middle Ear Middle ear contains three tiny bones known as ossicles Malleus Incus Stapes: connects the middle ear to inner ear The function of ossicles is to further amplify the sound received through the eardrum!  Inner Ear Semicircular canals Three tiny, fluid-filled tubes in your inner ear Help you keep your balance (vestibular sense) Cochlea A fluid-filled, snail-shaped structure - contains the auditory receptor cells (hair cells) Basilar membrane: a thin strip of tissue within the cochlea Auditory receptor cells (hair cells) of the inner ear embedded in the basilar membrane  Auditory Transduction 1. Sound waves travel along the auditory canal and strike the tympanic membrane, causing it to vibrate 2. The vibration causes the 3 ossicles to move. This presses the stapes into the oval window of the cochlea 3. The fluid inside the cochlea begins to move, stimulating the hair cells (auditory receptors) which become activated 4. The hair cells generate neural impulses that travel along the auditory nerve to the brain (vibration = neural impulse) 5. Auditory information is sent throughout the thalamus to the auditory cortex located in the temporal lobe  Pitch Perception How does the auditory system differentiate among various pitches? **Remember, intensity of sensation is determined by the frequency of action potentials in a given time period Temporal Theory Frequency of action potentials is coded by the activity level of auditory receptor (hair cell) Issue! The frequency of action potentials cannot account for the entire range that we are able to hear. There is a point at which a cell cannot fire any faster Place Theory Different portions of the basilar membrane are sensitive to sounds of different frequencies Hair cells at the base responds to high frequencies Hair cells at the tip responds to low frequencies Sound Localization: How can we tell where a sound is coming from? Monaural cues Binaural cues One eared cues (pinna) two eared cues How each ear translates the Relies on differences in patterns captured sound signal. of vibration of eardrum between Helpful to locating sounds that two ears. occur above, below, and in Provide information on the front or behind us location of sound along a horizontal axis. Interaural level difference sound coming from one side of the body is more intense at the closest ear because of the attenuation of the sound wave as it passes through the head. Interaural timing difference small difference in the time at which a given sound wave arrives at each ear. The Chemical Senses Gustation sense of taste stimuli: the molecules in the food Olfaction sense of smell stimuli: chemical molecules in the air  Taste (Gustation) Research demonstrates that we have about 5 groupings of taste: 1. Sweet 2. Salty 3. Sour 4. Bitter 5. Umami – associated with a taste for monosodium glutamate (MSG) Some research suggests we possess a taste for the fatty content of food.  Taste (Gustation) Taste buds: Transduction: Taste molecules bind to receptors and cause Groupings of taste receptor cells with chemical changes within the sensory cell. hair-like extensions that protrude into the central pore of the taste bud. These changes result in neural impulses being sent to the gustatory cortex, which is tucked Have a life cycle of 10 days to 2 weeks. underneath the overlap between the frontal and temporal lobes  Smell (Olfaction) Olfactory receptor cells: Transduction: Located in a mucous membrane at the Odor molecules bind to receptors. top of the nose Chemical changes cause signals to be Contain small hair-like extensions which sent to the olfactory bulb (where the serve as the site for odor molecules to olfactory nerves begin). interact with chemical receptors located Information is sent to the limbic system on these extensions and primary olfactory cortex.  Detecting Odors – Who is better? Rats = 8 to 50 times more sensitive to odors than humans Dogs = 300 to 10,000 times more sensitive than humans However, individual receptors for all these animals are equally sensitive. The difference lies in the number of receptors they each have. - Humans have ten million and dogs have one billion olfactory receptors! Touch There are many types of sensory receptors located in the skin, each attuned to specific touch-related stimuli Meisnerr’s corpuscles: respond to pressure and lower-frequency vibrations Pacinian corpuscles: detect transient pressure and higher- frequency vibrations Merkel’s disks: respond to light pressure Ruffini corpuscles: detect stretch  Thermoception & Nociception As well as receptors located in the skin, there are other free nerve endings that have sensory functions (e.g., temperature, pressure, and pain) Thermoception: Nociception: temperature perception sensory signal indicating potential harm and maybe pain This type of sensory information travels up the spinal cord directly to the brain, specifically the medulla, thalamus and the somatosensory cortex.  Pain perception motivates us to remove ourselves from the cause of injury. Inflammatory pain: signals some type of tissue damage. Neuropathic pain: caused by Pain Perception damage to neurons of either the peripheral or central nervous system = exaggerated in the brain Different pain medications needed for different types Congenital insensitivity to pain: a rare genetic disorder in which the individual is born without the ability to feel pain Can detect differences in temperature and Pain Perception pressure but cannot experience pain. Individuals are at greater risk of injury and have shorter life expectancies.  The Vestibular Sense Contributes to our ability to maintain balance and body posture. The major sensory organs of the vestibular system are located next to the cochlea in the inner ear. Utricle, saccule, and three semicircular canals (horizontal, posterior, superior canal) These organs are fluid-filled and contain hair cells which respond to movement of the head and gravitational forces  Kinesthesia and Proprioception The vestibular system also collects information important for controlling movement and reflexes that move parts of our bodies to compensate for changes in body position Kinesthesia: Proprioception: perception of the perception of body’s body position movement through space This information travels to the brain via the spinal column