Ganglion Cells Blind Spot Cornea Pupil Visual Area of the Bipolar Cells Thalamus Rods and Cones Lens Visual cortex of the occipital lobe

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1 How We See

2 How We See Cornea Ganglion Cells whose axons form the optic nerve Blind Spot the exit point at the back of the retina Pupil which is controlled by the iris Bipolar Cells Visual Area of the Thalamus Lens Rods and Cones sense receptors on the retina Visual cortex of the occipital lobe

3 Vision The entire process begins with a single light wave that travels through the sense organ of the eye and is translated by specialized receptor cells to be transported to the brain for color perception.

4 Light Waves Light waves from the visual spectrum for humans can be described in terms of three physical properties and their equivalent psychological properties. Wavelength = hue Amplitude (intensity) = brightness Purity = saturation

5 Light Waves Hue Red has the longest wavelengths and violet has the shortest Brightness Bright colors have taller waves (greater amplitude) and dull colors have shorter waves (smaller amplitude) Saturation (one wavelength vs. many) Colors that are highly saturated tend to be bright, intense, and vivid. Colors that are less saturated are more pastel, pale, and soft.

6 The Eye

7 Visual Impairments Cataracts is the most common cause of vision loss in people over age 40 and is the principal cause of blindness in the world.

8 How We See Light waves are bent and focused by the cornea which protects the eye s interior. The focused light waves then travel through the pupil controlled by the surrounding iris (the colored portion of the eye which is a ring of muscles that controls the size of the pupil allowing various degrees of light to enter the eye. The lens further bends the light waves and focuses them on the retina which is located along the back of the eye. The lens is adjustable and changes shape, either flattening or curving, in a process called accommodation.

9 How We See Rods or cones at the back of the retina convert light waves into neural signals in the process of transduction. The nearly 6 million cones detect color and detail and are most effective in daylight. There are three different types of cones that respond to long (red), medium (green), and short (blue) wavelengths. Cones are mainly located in the fovea, a small central region of the retina where visual acuity is the sharpest.

10 How We See The nearly 120 million rods are primarily concentrated on the outer edge or periphery of the retina. Rods are very sensitive under low light conditions but do not provide as much acuity or detail and cannot perceive color. When you notice an object in your peripheral vision, the object will appear as a shape lacking detail because only rods along the outer edge of the retina were activated. The processes by which rods and cones increase or decrease in sensitivity to light are called light and dark adaptation which is why entering or exiting a dark movie theater on a bright sunny day will require a period of time before vision adjusts.

11 How We See Bipolar cells collect neural signals from the rods and cones and transfer the messages to the ganglion cells. Ganglion cells organize the neural signals, and their axons converge to form the optic nerve. The optic nerve carries the neural messages through the thalamus to the primary visual cortex located in the occipital lobes. There are no photoreceptors where the optic nerve leaves the eye (the optic disk). As a result, a blind spot, or gap within the field of vision, exists within each eye. However, individuals are unaware of this blind spot because the brain fills in the gap with information provided by the other eye or the surrounding visual field. Part of the optic nerve from each eye crosses through the optic chiasm to the opposite hemisphere of the brain. Information from the right visual field (taken in by the left side of each eye) will travel to the left hemisphere of the brain, and information from the left visual field (taken in by the right side of each eye) will travel to the right hemisphere of the brain.

12 Vision Activities Peripheral Vision Blind Spot Color Blindness (you are responsible for the reading on this topic on your own)

13 How We Hear

14 How We Hear How We Hear Outer Ear Basilar Membrane whose axons form the auditory nerve Hair Cells lining the surface of the basilar membrace Auditory Canal Oval Window outer membrane of the cochlea Thalamus Eardrum (Tympanic Membrane) Hammer, Anvil, Stirrup three tiny bones Auditory cortex of the temporal lobe

15 How We Hear The sense of audition, or hearing, results from sound waves created by vibrating objects being converted into neural messages. Sound waves, like light waves, have three physical dimensions and equivalent psychological properties. Frequency determines pitch (highness or lowness of a sound) Measured in Hertz (Hz); Longer wavelengths or low frequencies create lower pitched sounds. Shorter wavelengths or high frequencies create higher pitched sounds. Amplitude (intensity) determines loudness Measured in Decibels (db) Higher amplitude or tall waves create louder sounds. Lower amplitudes or short waves create softer sounds. Purity determines timbre Pure tones are possible in lab experiments but difficult in the natural world

16 How We Hear 1. Sounds waves first enter the outer visible portion of the ear, called the pinna, and then move down the auditory canal (ear canal) to the tympanic membrane (eardrum) that vibrates in response to the funneled sound waves. 2. The middle ear (between the tympanic membrane and the cochlea) contains the ossicles (the three smallest bones in the body) which help amplify sound waves traveling to the inner ear.

17 How We Hear 3. The inner ear contains two sense organs: the cochlea concerned with hearing and the semicircular canals concerned with balance. The cochlea is a fluid filled and coiled tube where sound waves are converted into neural impulses. Covering the opening to the inner ear is a membrane called the oval window. Pressure here causes waves in the fluid to move to the basilar membrane. The sound waves cause the cilia (hair cells) to bend, initiating the process of transduction. 4. The signals travel along the auditory nerve through the thalamus to the temporal lobe s auditory cortex.

18 Hearing Theories Frequency Theory According to the frequency theory, the basilar membrane vibrates at the same frequency as the sound wave. The frequency theory explains how low frequency sounds are transmitted to the brain. However, since individual neurons cannot fire faster than about 1,000 times per second, the frequency theory does not explain how the much faster high frequency sounds are transmitted. The volley theory suggests that sounds above 1,000 hertz require the activity of multiple neurons working together. Place Theory According to the place theory, different frequencies excite different hair cells at different locations along the basilar membrane. High frequency sounds cause maximum vibrations near the stirrup end of the basilar membrane. Lower frequency sounds cause maximum vibrations at the opposite end.

19 Sound Localization Involves interpretation by the brain of sound waves entering both ears in order to determine the direction the noise is coming from. Possible because the sound waves arrive at one ear faster than they reach the other ear, and this information about timing is then interpreted by the brain. Sounds that originate directly above, below, in front of, or behind a person are the most difficult to locate because they reach each ear at the same time and with the same intensity. In order to determine the location of these sounds, humans also utilize their sense of vision or move their heads to cause the messages to arrive at different times.

20 Deafness Conduction Deafness The result of problems with funneling and amplifying sound waves to the inner ear Typically the result of damage to the eardrum or the bones of the middle ear A person will have equal difficulty hearing both high and low pitched sounds (sounds have become softer). Treatments include medication, surgery, or the use of a hearing aid to amplify the sound waves to the cochlea Sensorineural (nerve) Deafness The result of damage to the aspects of the auditory system related to the transduction of sound waves, or the transmission or neural messages. Typically the result of damage to the cilia caused by prolonged exposure to loud noise, aging, or disease. Hair cells (cilia) do not regenerate so the damage is permanent. A person will have a much harder time hearing high pitched sounds than low ones. Treatment is most likely hearing aids but severe damage can be treated with cochlear implants.

21 How We Taste

22 How We Taste The chemical senses of taste and smell respond to chemical molecules dissolved in liquid (taste) or that are found in the air (smell). The chemical senses serve two purposes: (1) identification of molecules safe to consume and (2) identification and rejection of molecules that are dangerous.

23 How We Taste Transduction for the chemical sense of gustation occurs when molecules mix with saliva. Taste receptor cells are mostly located within taste buds and are not visible to the human eye. Taste buds are clustered in small bumps, known as papillae that are along the surface of the tongue. There are also receptors for taste at the back of the throat and along the roof of the mouth.

24 How We Taste Five Basic Tastes: Sweet Sour Bitter Salty Umami (most recent discovery; a flavor enhancer associate with glutamate; meaty or savory)

25 How We Taste Considerable variation exists between individual in terms of how sensitive they are to various tastes, and this sensitivity is mostly determined by genetics. Both humans and other animals prefer sweet and salty tastes to sour and bitter ones. Evolutionary psychologists believe that these preferences evolved to help humans and animal more easily identify nutritious foods and avoid that that are rotten or poisonous. Taste receptors regenerate every 1 2 weeks but overall responsiveness to taste declines with age and activities such as smoking and drinking alcohol.