visual spectrum: range of electromagnetic radiation that is visible to us, 380 to 760 nanometers

Perception of color determined by 3 dimensions:

1) hue - determined by wavelength (what we think of as color)

2) brightness - determined by intensity

3) saturation - relative purity of the light that is being perceived

3 types of eye movements:

1) vergence movement - cooperative, keep both eyes fixed on target

2) saccadic movements - abrupt shifts in gaze from one point to another, as when reading

3) pursuit movement - following the movement of an object

retina - interior lining of the back of the eye containing photoreceptors

cones - 6 million, daytime vision, acuity, color, concentrated in fovea (central region of retina)

rods - 120 million, more sensitive to light than cones

• in dim light we are colorblind and lack foveal vision (see faint star with peripheral vision which disappears when you look at it directly)

1) photoreceptors, which synapse onto

2) bipolar cells, which synapse onto

3) ganglion cells, whose axons travel thru the optic nerves to the brain

• horizontal and amacrine cells - transmit info across cells, from adjacent photoreceptors

• (see Figure 6.6)

• what is the pathway of light?

1) lamellae (thin plates of membrane on photoreceptors) contain photopigments consisting of an opsin (protein) and retinal (lipid) - for example, rhodopsin

2) when rhodopsin is exposed to light, it breaks into rod opsin and retinal

3) when the photopigment is split, it changes the membrane potential (receptor potential), which changes the rate the photoreceptor releases its transmitter substance

4) photoreceptors have ion channels that are always open, and ions (+) freely enter the cell

5) when the photopigment splits, sodium channels close, keeping ions from entering the cell, and causing the membrane to hyperpolarize

6) this stops release of the transmitter substance

7) the transmitter substance of the photoreceptors usually causes a hyperpolarization in the bipolar cells

8) if transmitter substance release stopped, then bipolar cells depolarize and release more of their transmitter substance

9) this causes depolarization of the ganglion cell, which increases its rate of firing

• photoreceptors and bipolar cells release transmitter substances according to their membrane potentials; ganglion cells have action potentials

• magnocellular layers - inner two layers; found in all mammals; sensitive to movement
• parvocellular layers - outer 4 layers; color vision; found only in primates

3 types of ganglion cells:

1) on-cells

2) off-cells

3) on/off cells

Color

color mixing - addition of two or more light sources; red/green=yellow; yellow/blue=white

blue cones - detect short wavelengths

green cones - detect medium wavelengths

red cones - detect long wavelengths

• we have more red and green cones than blue

protanopia - confuse red/green; see blue and yellow; normal acuity; red cones are filled with green cone opsin; X-linked

deutranopia - same perception as protanopia, but green cones are filled with red cone opsin; X-linked

tritanopia - rare, not X-linked; see world in reds and greens; have problems with blues; retinas lack blue cones; lack thereof does not affect acuity (because we have so few blue cones normally)

Opponent-process

red-green

yellow-blue

black-white - detect brightness

see Figure 6.19

see (and know!) Figure 6.20

[did you do the afterimage? Cool, huh.]

Analysis of Visual Information

• 25% of visual cortex gets info from fovea
• most neurons are sensitive to orientation of visual stimuli, and some to movement
• visual cortical neurons respond best to sine-wave grating - lack of sharp changes in spatial frequencies (Lincoln photo, p. 167)
• retinal disparity - neurons respond to a stimulus that produces images on slightly different parts of the retina of each eye
• blobs - special groups of cells in visual cortex, receiving color info thru parvocellular layers

Visual Association Cortex

1) ventral stream - ends with the inferior temporal cortex, involved with perception of objects ("what")

2) dorsal stream - ends with the posterior parietal cortex, involved with perception of location, movement, and control of eye and hand movements

Visual Agnosia

1) apperceptive visual agnosia - difficulty perceiving the shapes of objects, even though fine details can be detected

• prosopagnosia - inability to recognize faces; mild form of apperceptive visual agnosia

Balint’s syndrome (disruption of dorsal stream)

• optic ataxia - deficit in reaching for objects under visual guidance
• ocular apraxia - deficit of visual scanning
• simultanagnosia - only one object perceived at a time

• pitch - determined by the frequency of vibration, measured in hertz
• loudness - determined by intensity
• timbre - mixture of vibration frequencies
• eye is "synthetic" (don’t perceive individual components); ear is "analytical" (perceive different tones in a chord, for example)

tympanic membrane - eardrum, vibrates with sound

ossicles - bones of the middle ear, set into vibration by the tympanic membrane

1. malleus - "hammer", connects with tympanic membrane and transmits vibrations to
1. incus - "anvil," and to
2. stapes - "stirrup," which pass information through the oval window to the cochlea

1. basilar membrane - caused to move relative to the
1. tectorial membrane, which is fairly rigid.
2. The cilia of the hair cells, on the basilar membrane, are bent, which causes stimulation of the dendrites of neurons of the cochlear nerve

• we have inner hair cells (3500), which are responsible for normal hearing, and outer hair cells (12,000), which are involved in coding of pitch

• cilia attached to each other by tip links at attachment sites called insertional plaques

• tension on the tip links is what controls ion channels, not simply the movement of the cilia

• each hemisphere receives info from both ears, but mostly from the contralateral one

• the relationship between the basilar membrane and the cortex is tonotopic representation, relative position on the basilar membrane is reproduced in the auditory cortex

1) Place Coding - different frequencies of sounds move different parts of the basilar membrane: basal end (closest to stapes) responds to high frequencies, opposite end responds to low frequencies

• problem: no basilar hair cells respond to very low frequencies, yet we can perceive them

• if white noise is pulsated on and off, we detect a tone corresponding to the frequency of the pulses - white noise stimulates across the whole basilar membrane (all hair cells), so we don’t get any specific info that way; it is the firing rate that coded the pitch

• axons of the cochlear nerve encode loudness by rate of firing

• but would be confusing for those low frequencies (remember, coded by rate of firing)

• for these sounds, loudness is coded by the number of axons that are firing at a given time

• fundamental frequency - corresponding to the perceived pitch of the note, combined with overtones, which are multiples of the fundamental frequency, are encoded and remembered to identify different timbres

1) Arrival time - for short sound, soundwave arrives at one ear first

2) Phase differences - used for continuous low frequencies, refers to simultaneous arrival at each ear of different portions of a sound wave

3) Intensity differences - used for continuous high frequencies, when head gets in the way of the soundwaves, creating a "sonic shadow", so that ear on the other side receives less intense stimulation

• vestibular sacs - respond to force of gravity and inform the brain about the head’s orientation

• utricle
• saccule
• contain hair cell receptors and calcium carbonate crystals in an overlying gelatinous mass
• when the head changes orientation, the crystals shift, placing force on the hair cells
• semicircular canals - respond to changes in rotation of the head, but not steady rotation
• correspond to 3 major planes of the head: sagittal, transverse (cross-section), horizontal
• contain ampulla, which is a widened area into which the cupula protrudes
• the cupula contains the cilia of hair cell receptors
• fluid flowing within canals causes cupula to bend , which stimulates hair receptors
• cupula is bent at start of movement, when fluid resists rotation of head, and again when head stops, as fluid continues to move

• you don’t have to know the vestibular pathway

3 forms of somatosensation:

1) kinesthesia - body position, movement - from joints, tendons, muscles

2) organic senses - sensations from internal organs - stomachaches

3) cutaneous senses: which are…

Skin receptor types:

1) Ruffini corpuscles - in hairy skin, respond to low-frequency vibration

2) Pacinian corpuscles - largest sensory organs in the body, in glabrous skin (hairless, on fingertips, palms); sensitive to high-frequency vibration, but not steady pressure

3) Meissner’s corpuscles - in glabrous skin, respond to low-frequency vibration

4) Merkel’s discs - respond to indentation of the skin, adjacent to sweat ducts

• combination of skin sensation and kinesthesia to identify textures (smooth, rough, sticky, etc.)

• changes in temperature detected by free nerve endings
• other populations of receptors detect warmth and coolness

• free nerve endings
• pain is needed for survival
• periaqueductal gray matter - contains neurons with opiod receptors
• opiatelike peptides identified:

• endorphins
• enkephalins
• dynorphins

• opioids inhibit inhibitory interneurons in the periaqueductal gray matter

• you don’t have to know the pain pathway

• at least 2 brain mechanisms for analgesia exist: opioid and non-opioid
• acupuncture and placebos work through the opioid system
• hypnosis does not work through the opioid system

• analgesia is needed for several reasons:

• don’t want to be distracted by chronic, non-threatening pain
• don’t want to be distracted by acute pain during mating or fighting or fleeing
• if we get a signal that pain is about to be inflicted, opioids are released

4 tastes:

1) sweet - associated with "food," such as fruit; tip of tongue; detection involves G-proteins and second messengers

2) salty - associated with sodium chloride, which may be needed by the body; tip of tongue; detection involves sodium channels

3) sour - associated with spoiled food - usually avoided; sides of tongue; detection involves potassium channels

4) bitter - associated with poisons; back of tongue, throat, palate; detection involves G-proteins and second messengers

• tongue, palate, and throat contain about 10,000 taste buds each with receptor cells which have a life span of 10 days

• you don’t have to know the taste pathway, other than that the nucleus of the solitary tract receives information first

• you don’t have to know the neural coding of taste

• odors and memory

• odors are hard to describe - appears that olfactory system designed to identify things, not analyze qualities

• 50 million olfactory receptors in olfactory epithelium at the top of the nasal cavity

• very little air flows up to olfactory epithelium, so we "sniff"; or we can stop breathing through our nose

• olfactory receptors have a lifespan of 60 days

• olfactory mucosa also contains free nerve endings which detect painful stimuli (such as sniffing ammonia)

• you don’t have to know the olfactory pathway or transduction of olfactory information

• are there specific receptors for each odor?

• odor encoded by spatial and temporal activities of different neurons

• is olfaction synthetic? Or analytic?