Updated for 1999
Lecture Notes for Week 6
Chapters 6 and 7


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

3 Layers of retina:

1) photoreceptors, which synapse onto

2) bipolar cells, which synapse onto

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

Detection of light by photoreceptors:

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

dorsal lateral geniculate nucleus - in thalamus, receive info from ganglion cells, 6 layers, each receiving info from only one optic chiasm - axons from ganglion cells serving nasal portion of visual fields cross to opposite hemisphere

3 types of ganglion cells:

1) on-cells

2) off-cells

3) on/off cells


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

Color blindness

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)




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

Skip modular organization, pp. 169-170

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

2) associative visual agnosia - relatively good object perception, but inability to recognize what is perceived - disruption of ventral stream (connection with verbal area)

Balintís syndrome (disruption of dorsal stream)


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
    2. incus - "anvil," and to
    3. stapes - "stirrup," which pass information through the oval window to the cochlea
cochlea - receptive organ is organ of Corti, which contains:
    1. basilar membrane - caused to move relative to the
    2. tectorial membrane, which is fairly rigid.
    3. The cilia of the hair cells, on the basilar membrane, are bent, which causes stimulation of the dendrites of neurons of the cochlear nerve
Detection of pitch

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

2) Rate Coding - lower frequencies detected by neurons of the apical end of the basilar membrane (opposite end from stapes) which fire in synchrony to the movement of the membrane Detection of loudness Detection of timbre Detection of location

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




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 areÖ

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) Meissnerís corpuscles - in glabrous skin, respond to low-frequency vibration

4) Merkelís discs - respond to indentation of the skin, adjacent to sweat ducts

Detection of temperature Pain

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

Detection of odors