Perception

Question 1

Another word for Hearing

Answer 1

Audition

Question 2

Another word for Smelling

Answer 2

Olfaction

Question 3

Another word for Tasting

Answer 3

Gustation

Question 4

Another word for Touch

Answer 4

Somatosensation

Question 5

List the 3 Major Sensory Regions of the Cerebral Cortex

Answer 5

Thalamus

Post-central Gyrus Somatosensory Cortex Areas S1 and S2

Question 6

Sensory Processing:

8 Steps

Answer 6

A General Overview of All the Senses:

– External sense organ (eye, ear, skin, etc)
– Receives physical/chemical input
– Transformed into neural signal
– Transmitted through relay stations
– Processed in a primary cortical area
(V1, A1, S1, etc)
– Refined in secondary sensory areas
– Modified/Regulated in association & frontal areas
– …Perception!

Question 7

Auditory

Pathway

Answer 7

Stimulus = sound wave

1. Outer ear (air) -­pressure
2. Middle ear (bones) -­vibrate
3. Inner ear (fluid) -­waves
4. Cochlea (hair cells)
   a. Hair cells move*
   b. Neurotransmitters enter
   c. Action potentials
5. Auditory nerve
6. Midbrain relays (Cochlear nucleus, Inferior colliculus)
7. Thalamus (Medial Geniculate Nucleus)
8. Primary Auditory Cortex (A1; Heschl’s Gyrus)
9. Secondary Auditory Cortex (A2)

Question 8

Cochlea Organization

Answer 8

Cochlea is organized by frequency (tonotopic map): hair cells at base activated by high frequencies; at apex, low frequencies

Question 9

MGN

Answer 9

Medial Geniculate Nucleus

Question 10

Tonotopic Organization

Answer 10

The inner ear and the auditory area of the brain and central nervous system are arranged in pitch order, from low to high.

Question 11

Tonotopy

Answer 11

Derives from the Greek:
tono = pitch or tension and topos = place

Tonotopy is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighboring regions in the brain. Tonotopic maps are a particular case of topographic organization, similar to retinotopy in the visual system.

Tonotopy in the auditory system begins at the cochlea. Different regions of the basilar membrane in the organ of Corti, the sound-sensitive portion of the cochlea, vibrate at different sinusoidal frequencies due to variations in thickness and width along the length of the membrane. Nerves that transmit information from different regions of the basilar membrane therefore encode frequency tonotopically. This tonotopy then projects through the vestibulocochlear nerve and associated midbrain structures to the primary auditory cortex via the auditory radiation pathway. Throughout this radiation, organization is linear with relation to placement on the organ of Corti, in accordance to the best frequency response (that is, the frequency at which that neuron is most sensitive) of each neuron. However, binaural fusion in the superior oliviary complex onward adds significant amounts of information encoded in the signal strength of each ganglion. Thus, the number of tonotopic maps varies between species and the degree of binaural synthesis and separation of sound intensities; in humans, six tonotopic maps have been identified in the primary auditory cortex. Their anatomical locations along the auditory cortex.

Question 12

cochlea

Answer 12

small snail-like structure in the inner ear that sends information about sound to the brain.

Question 13

Interaural Time Difference

Answer 13

the difference in arrival time of a sound between two ears.

It is important in the localization of sounds, because it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This path-length difference results in a time difference between the sound’s arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.

Question 14

Interaural Intensity Difference

Answer 14

When the sound source is not centered, the listener’s head partially ``shadows’’ the ear opposite to the source, diminishing the intensity of the sound in that ear (particularly at higher frequencies).

The pinnae filters the sound in a way that is directionally dependent. This is particularly useful in determining if a sound comes from above, below, in front, or behind.

(sound louder in closer ear)
- Neurons compare firing rates from both ears

Question 15

Auditory Cognitive Functions

Answer 15

• Sound localization
• Detection/Discrimination
• Language
• Music

Question 16

Olfactory Stimuli

Answer 16

Stimuli = odor molecules

smell is a chemical sense

Question 17

Combinatorial Coding

Answer 17

> 1000 types of receptors:
different odorants bind to different combinations of
receptors

more combinations at glomeruli

Question 18

Olfactory Pathway

Answer 18

1. Nose
2. Nasal cavity (odor receptors)
3. Odorant binds to bipolar neuron (combination coding)
4. Signaling cascade&raquo_space;» action potential
5. Signal sent to olfactory bulb (glomeruli)
6. Olfactory Nerve
7. Primary olfactory cortex
8. Orbitofrontal cortex (secondary olfactory)

Question 19

glomeruli

Answer 19

consists of the neurons of the olfactory bulb

Question 20

Does the Olfaction pathway go through the Thalamus?

Answer 20

NO

Olfaction is exception
Most primitive sense
Linked to memory & the limbic system (emotion)

Question 21

Olfactory Cognitive Functions

Answer 21

• Memory/Emotion links
• Detection/Discrimination
• Sniffing
• Pheromones

Question 22

Gustatory Stimulus

Answer 22

Stimulus = food molecules/tastants

chemical sense

Question 23

Gustatory Pathway

Answer 23

1. Mouth (taste buds)
2. Tastant binds to taste cell*
3. Chemical transduction
   E.g., Salty:
   NaCl breaks down
   into Na+ and Cl-­.
   Na+ enters ion channel, depolarizes cell
4. Action potential
5. Gustatory nerves
6. Brainstem relays (Gustatory nucleus)
7. Thalamus (VPM)
8. Primary gustatory cortex (insula & operculum)
9. Orbitofrontal cortex (secondary gustatory)

Question 24

Name the 5 different types of taste cells:

Answer 24

Salty
Sweet
Sour
Bitter
Umami

Each taste has different type of chemical transduction

Question 25

Gustatory Cognitive Functions

Answer 25

• Nutrition
• Enjoyment/Reward/Preference
• Discrimination

Question 26

Somatosensory Stimumlus

Answer 26

Stimulus = touch/pressure, temperature, pain, position

Question 27

Somatosensory Pathway

Answer 27

1. Skin (different types of receptors)*
2. Mechanical change to receptor
3. Transduced to neural signal
4. Spinal nerve (Dorsal Root Ganglion)
5. Spinal cord
6. Brainstem/midbrain relays (cross to contralateral side)
7. Thalamus (VP)
8. Primary somatosensory cortex (S1)
9. Secondary somatosensory cortex (S2)
10. (Also cerebellum, etc)

Question 28

*Different Somatosensory receptor types:

Answer 28

-­ Mechanoreceptors/corpuscles
(regular touch, light touch, deep pressure, vibration)
-­ Nocioceptors (pain)
-­ Thermoreceptors (temperature)
-­ Proprioceptors (body position)

Question 29

Somatotopic Organization

Answer 29

related to particular areas of the body; describing the organization of the motor area of the brain, specific regions of the cortex being responsible for the motor control of different areas of the body.

Question 30

Somatotopic (Re)Organization:

Cortical Plasticity

Answer 30

refers to the brain’s ability to develop and adapt.

Example: Violinists’ brains have more cortex devoted to their fingers

Question 31

Somatosensory Cognitive Functions

Answer 31

• Posture/Motor control
• Pleasure/Pain
• Avoidance/learning
• Object recognition (texture, shape)

Question 32

Sensation&raquo_space;»> Perception:

How much detail do I need to know?

Answer 32

• Don’t need to know which thalamic nuclei each sense goes through or the names/locations
of the brainstem/midbrain relays.

• Do need to know the gist/basic steps of the pathway, as well as the names/locations
of the primary/secondary cortical areas?

Question 33

Visual Stimulus

Answer 33

Visual Stimulus = light

Question 34

Visual Pathway

13 Steps

Answer 34

1. Eye (remote sensation)
2. Lens inverts & focuses
3. Retina (photoreceptors)*
4. Light causes changes in photopigments
5. Electrical current &raquo_space;»> neural signal
6. Bipolar & ganglion cells (& horizontal connections)
7. Retinal ganglion cells fire action potentials
8. Optic nerve
9. Optic chiasm (contralateral crossover: LVF to
   R-­hem)
10. Thalamus (LGN)
11. Optic Radiation
12. Primary visual cortex (V1)
13. Secondary visual areas (V2, V3, etc)

Other pathways:
optic nerve to superior colliculus, other subcortical areas

Question 35

Photoreceptors:

Answer 35

2 basic types of photoreceptors:
rods & cones (there are 3 types of cones for color vision)

So 4 different total photoreceptors

Question 36

Optic Chiasm

Answer 36

The optic chiasm or optic chiasma is an X-shaped space just in front of the pituitary gland where optic nerve fibers pass through to the brain. The fibers from the nasal half of each retina cross over, but those from the temporal sides do not. Specifically, fibers from the nasal half of the left eye and the temporal half of the right eye form the right optic tract; and the fibers from the nasal half of the right eye and the temporal half of the left form the left optic tract. The nerve fibers then continue in the optic tracts.

Question 37

Retinotopic Organization

Answer 37

Spatial maps preserved:

image&raquo_space;» retina&raquo_space;» visual cortex

Question 38

Cortical Visual Pathways

Answer 38

IT cortex in macaques ≈
LOC (Lateral Occipital Complex = object processing area) in humans;

Increase in complexity & receptive field size:
Visual Hierarchy

Question 39

How are sound waves converted to neural signals?

Answer 39

Just as we do not actually smell with the bumps on our faces called noses, neither do we perceive sound solely with the flaps we call ears. Although hearing begins with the ear flap or pinna, the receptor cells that change sound energy into the electrical currency of the nervous system lie deep inside the temporal bone of the skull. Like olfactory cells that detect odors, auditory receptor cells (hair cells) are recessed from the surface of the body. Unlike olfactory or taste receptors, however, hair cells are not renewed when they die or are damaged. Although taste and olfactory cells interact directly with molecules in the environment, auditory receptors are quite far removed from the phenomena they detect. Sound waves are converted into vibrations in a fluid in the inner ear, and these vibrations indirectly move the hair cells, which then send electrical signals to the brain.

Sound activates the external, middle, and inner ear.

External Ear
The folds and ridges of the pinna channel sound efficiently into the ear canal and to the eardrum, or tympanic membrane, at its end. The pattern of folds captures sounds in a way that helps us localize the origin of sound in space, especially on the vertical axis. The ear canal carries sound to the eardrum, and its lining produces ear wax to keep the eardrum and canal from drying out and to trap dirt before it gets to the eardrum. When sound waves vibrate the eardrum, sound energy is transferred to the middle ear.

Middle Ear
The middle ear is a small, air-filled pocket bounded by the eardrum on one side and the oval window of the inner ear on the other. This pocket is connected to the common mouth and nasal cavity, or pharynx, by the Eustachian tube. The Eustachian tube allows air pressure to equalize between the outside of the eardrum (surrounding atmosphere) and the inside of the eardrum (the middle ear). This is also the pathway that allows infections from the mouth and nose cavities to enter the middle ear, causing the common ear infections of childhood. The middle ear houses the 3 smallest bones in the body, the malleus, incus, and stapes (hammer, anvil, and stirrup), which form a chain of levers connected by joints. The malleus is attached to the eardrum by ligaments, as is the stapes to the oval window. Thus, this series of membranes and bones forms a pathway that carries vibrations from the eardrum to the inner ear. The stapes, the last bone in the chain, pulls or pushes on the membranous oval window when the eardrum and the 3 bones are vibrated by sound waves; the oval window is a closed membrane, but acts as the entrance to the inner ear for sound energy.

Inner ear
What does this pulling and pushing on the oval window do in the inner ear? A look at the structure of this area helps show how sound wave energy is transmitted to fluid in the inner ear.

The inner ear is composed of the cochlea, from the Greek word for snail, and the semicircular canals. (These latter canals are part of the vestibular system for balance and will not be considered here.) The cochlea is a membranous tube that is covered by a very thin layer of bone and wound around a tiny central bone (the modiolus) into a shape that resembles a snail; it is only about nine millimeters across - well under one-half inch. The cochlea is filled with a special fluid, and the pushing and pulling of the stapes on the oval window moves the fluid in this coiled tube.

If we stretch out the cochlear tube, we see that inside are actually 3 tubes, two larger and one smaller, with the small tube, (the scala media) lying between the two larger ones. All three tubes are filled with fluids, which vary somewhat in composition.

The cochlea is a tube made of three inner tubes: the scala vestibuli, scala media, and scala tympani.

The fluid in the top-most tube is set in motion by the piston-like movements of the stapes on the oval window. The vibrations travel into the fluid of the upper tube of the cochlea and around the tip of the organ into the fluid of the lower tube. The pushing or pulling of the oval window on this fluid must have a release or dampening mechanism: this is provided by the round window, a membrane located at the end of the lower of the large tubes.

Forming the lengthwise partition between the lower large tube and the small tube is the basilar membrane. On this membrane sit the stars of the show in the auditory system, the auditory receptor cells, or hair cells. When the basilar membrane moves, it stimulates the hair cells, which then send signals about sounds to the brain.

We can summarize the workings of the ear as follows:

The pinna captures sound waves and channels them through the ear canal to the eardrum.
Vibrations of the eardrum pass along the three bones of the middle ear, with the base of the stapes then rocking the oval window in and out.
The membranous oval window acts something like a piston in a hydraulic system: it pushes and pulls on the enclosed fluid of the cochlea.
The fluid vibrations move the basilar membrane, and this motion activates auditory receptor cells (hair cells) sitting on the membrane, which send signals to the brain.

Hair cells sit on the basilar membrane and are innervated by fibers from the auditory nerve, one of the cranial nerves.

4. The basilar membrane distributes vibrations to hair cells

The motion of the fluid in the cochlear tubes sets the basilar membrane in motion, generating traveling waves along its length. These are somewhat like the waves produced in a long rope that is grasped at one end and flicked. The basilar membrane is much more complicated, though. To begin with, it is not uniform throughout its length, but rather is relatively wide and thin at the apex (top) of the cochlea, and narrow but thick at the base. Because of these properties, a sound wave in the cochlear fluid produces a peak amplitude or height of displacement of the membrane at a certain point along its length. This point is determined by the frequency (number of waves per unit time) of the sound that originally produced the fluid motion. High frequencies cause a peak wave near the base (narrow part of the membrane), and low frequencies produce their peaks toward the apex (broad part of the membrane). Thus, the basilar membrane is sometimes called a frequency analyzer. In addition, the hair cells on the membrane are also tuned to particular frequencies, so that each hair cell responds best to sound of a given frequency.

This anatomy or “geography” of the basilar membrane and hair cells produces a tonotopic map along the membrane. This means that, as with geographic maps, once you know some landmarks and the scale of the map, you can calculate the point where sound of a particular frequency will have its peak, because the system is ordered and predictable. Further, groups of responding neurons in the brain auditory areas also contain tonotopic maps.

5. Hair cells encode sounds and transmit this information to neurons

The hair cells sit on an epithelial ridge called the organ of Corti on the basilar membrane; the ridge contains several other types of cells that support the hair cells. The receptor cells are called hair cells not because they sprout hairs, but because their apical or top ends are covered with cilia, which under the microscope look a bit like hairs. Over the top of the cilia lies a gelatinous membrane, sandwiching the hair cells between itself and the basilar membrane. The complex, relative movements of these two membranes activate the cilia of hair cells, causing the cells to undergo a change in the electrical potential across their cell membranes. When specific changes occur in this electrical state, neurotransmitter molecules are released from the bottom or basal parts of the hair cells. Thus, the cilia are essential in transducing, or changing, the mechanical energy of the basilar membrane into electrical changes in the hair cells. As mentioned above, hair cells are tuned to the particular frequencies that activate the portion of the basilar membrane where they reside.

Hair cells are modified epithelial cells and do not have dendrites and axons as neurons do, but they communicate, as many neurons do, by releasing neurotransmitter. They release the neurotransmitter at junctions or synapses that they form on branches from neurons whose cell bodies are in a ganglion (group of neurons) just outside the cochlea. The axons from the ganglion neurons form the auditory nerve, which carries signals into the first stop in the brain, the cochlear nucleus.

6. Sound information from each ear is distributed to both sides of the brain

Once information from one ear goes to the cochlear nucleus on that side of the head, the neurons in this nucleus send information to identical higher centers on both sides of the brain. Some of the processing stations are the superior olivary nucleus, inferior colliculus (in the midbrain), medial geniculate nucleus (in the thalamus), and the auditory cortex. From the auditory cortex, messages go to other areas of the cerebral cortex for interpretation of the meaning of sounds.

Signals from neurons that get information directly from hair cells travel in the auditory nerve to the brainstem. Here the signals activate more neurons, which send the auditory messages on to the thalamus, then to the auditory cortex in the temporal lobe of the cerebrum.

In the cochlear nucleus, the first brain relay station for sound, signals encoding sounds are not just passed on, but rather are “dissected” and sorted first. This means that different features of a sound, such as frequency, intensity, or onset and offset (beginning and ending of a sound) are carried to higher brain centers separately. This sorting out of the features of stimuli and sending messages forward in parallel nerve pathways is a common and important attribute of brain sensory systems. One of the big tasks of researchers is to find out how areas in the cerebral cortex use input from these parallel pathways to interpret the original sensations - in this case, the original sounds.

7. We need two ears to locate a sound source

When a sound occurs at the extreme left of a subject, the arrival of the sound at the left ear is about 600 to 700 microseconds (millionths of a second) earlier than at the right ear. Further, the head acts as a sound barrier, so the sound is a little louder in the left ear. How does the timing and intensity of sound in the two ears tell the brain where the sound source is?

This processing is carried out in the superior olivary nucleus (SON) of the brainstem. Axons coming into the SON from the cochlear nuclei form synapses successively across a linear series of SON neurons. Each neuron here gets messages from cochlear neurons in both ears, and in order to fire a signal to higher brain centers, each must receive simultaneous messages from the two cochlear nuclei. Because a sound from, for example, the extreme left side of a person arrives later in the right ear than the left, hair cells and neurons from the right ear send their signals slightly later than those from the left ear. Each SON neuron is activated only by simultaneous input from the two ears, so that when, for example, signals from axon d1 from the right and d2 from the left ear coincide on SON neuron d, it fires. Through experience, we learn that when neuron d fires, the sound is, for example, at 50o to the left of straight ahead. If neuron b fires, this could mean that the sound originates at 20o to the left.

Neurons in another part of the SON employ intensity cues rather than arrival-time cues. Again, the neurons need simultaneous input from the two ears to fire, but in addition, they respond best when the sound intensity on one side of the head exceeds that on the other by a certain amount.

Note that it is hard to differentiate sounds coming from directly in front of you from those originating directly behind you. Both sounds are equal distance from the two ears, so there is no difference in timing and intensity, information that our brains need to localize sound in the horizontal dimension.

Sound is processed in the superior olivary nucleus (SON). A sound arriving earlier at the left ear elicits signals more quickly in the SON than those from the right ear. At some point, as the signals from the two ears travel across the linear array of neurons in the SON, they converge on one neuron and activate it. This processing is carried out simultaneously in the left and right SONs.

Question 40

What’s the one sense that doesn’t go through the thalamus?

Answer 40

Olfaction. Smell

Question 41

Which sense uses combinatorial coding?

Answer 41

olfactory system uses a combinatorial coding scheme to encode the identities of odors.

Question 42

Which sense organizes stimuli according to frequency?

Answer 42

Auditory. Hearing.

Question 43

Where are hair cells located?

Answer 43

Hair cells are the sensory receptors of both the auditory system and the vestibular system. The auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear.

Question 44

Paperclip Experiment

Answer 44

Two-point Discrimination
Here’s something we do know for sure about the sense of touch: it tends to be keenest in regions of the body that are densely populated with sensory neurons. One of the simplest ways of demonstrating this relationship is with something called the two point discrimination test. Best of all? You can try it out at home. You’ll need a partner, but here’s a simple experiment designed by neuroscientist Marjorie A. Murray:

Bend a paper clip into the shape of a U with the tips about 2 cm apart. Make sure the tips of the U are even with each other. Lightly touch the two ends of the paper clip to the back of the hand of your subject. Your subject should not look at the area of skin that is being tested. Do not press too hard! Make sure both tips touch the skin at the same time. Ask your subject if he or she felt one or two pressure points. If your subject reported one point, spread the tips of the clip a bit further apart, then touch the back of the subject's hand again. If your subject reported 2 points, push the tips a bit closer together, and test again. Measure the distance at which the subject reports "I feel two points."

Question 45

What are the effects of damage to

an Optic Nerve?

Answer 45

Complete blindness in one eye

Question 46

What are the effects of damage to

the Primary Visual Cortex?

Answer 46

If you damage a certain part of your primary visual cortex, you develop a local blindness, as though you had destroyed the corresponding part of your retina.

Question 47

What are the effects of damage to the V4?

Answer 47

Damage to V4 (especially bilaterally) can result in achromotopsia, which is an inability to see color.

Question 48

What are the effects of damage to the MT?

Answer 48

Akinetopsia is an intriguing condition brought about by damage to the Extrastriate cortex MT+ that renders humans and monkeys unable to perceive motion, seeing the world in a series of static “frames” instead and indicates that there might be a “motion centre” in the brain. Of course, such data can only indicate that this area is at least necessary to motion perception, not that it is sufficient; however, other evidence has shown the importance of this area to primate motion perception. Specifically, physiological, neuroimaging, perceptual, electrical- and transcranial magnetic stimulation evidence all come together on the area V5/hMT+. Converging evidence of this type is supportive of a module for motion processing. However, this view is likely to be incomplete: other areas are involved with motion perception, including V1, V2 and V3a and areas surrounding V5/hMT+ . A recent fMRI study put the number of motion areas at twenty-one.[10] Clearly, this constitutes a stream of diverse anatomical areas. The extent to which this is ‘pure’ is in question: with Akinetopsia come severe difficulties in obtaining structure from motion. V5/hMT+ has since been implicated in this function as well as determining depth. Thus the current evidence suggests that motion processing occurs in a modular stream, although with a role in form and depth perception at higher levels.

Question 49

How do afterimages/aftereffects work?

Answer 49

?

Question 50

Examples of multisensory integration & illusions:

Answer 50

Multisensory illusions

McGurk effect
It has been found that two converging bimodal stimuli can produce a perception that is not only different in magnitude than the sum of its parts, but also quite different in quality. In the classic study, the McGurk effect, a person’s phoneme production was dubbed with a video of that person speaking a different phoneme. The end result was the perception of a third, different phoneme. McGurk and MacDonald explained that phonemes such as ba, da, ka, ta, ga and pa can be divided into four groups, those that can be visually confused, i.e. (da, ga, ka, ta) and (ba and pa), and those that can be audibly confused. Hence, when ba – voice and ga lips are processed together, the visual modality sees ga or da, and the auditory modality hears ba or da, combining to form the percept da.

Ventriloquism
Ventriloquism has been used as the evidence for the modality appropriateness hypothesis. Ventriloquism describes the situation in which auditory location perception is shifted toward a visual cue. The original study describing this phenomenon was conducted by Howard and Templeton, after which several studies have replicated and built upon the conclusions they reached. In conditions in which the visual cue is unambiguous, visual capture reliably occurs. Thus to test the influence of sound on perceived location, the visual stimulus must be progressively degraded. Furthermore, given that auditory stimuli are more attuned to temporal changes, recent studies have tested the ability of temporal characteristics to influence the spatial location of visual stimuli. Some types of EVP - Electronic voice phenomenon, mainly the ones using sound bubles are considered a kind of modern ventriloquism technique and is played by the use of sophisticated software, computers and sound equipment.

Double-flash illusion
The double flash illusion was reported as the first illusion to show that visual stimuli can be qualitatively altered by audio stimuli. In the standard paradigm participants are presented combinations of one to four flashes accompanied by zero to 4 beeps. They were then asked to say how many flashes they perceived. Participants perceived illusory flashes when there were more beeps than flashes. fMRI studies have shown that there is crossmodal activation in early, low level visual areas, which was qualitatively similar to the perception of a real flash. This suggests that the illusion reflects subjective perception of the extra flash. Further, studies suggest that timing of multisensory activation in unisensory cortexes is too fast to be mediated by a higher order integration suggesting feed forward or lateral connections. One study has revealed the same effect but from vision to audition, as well as fission rather than fusion effects, although the level of the auditory stimulus was reduced to make it less salient for those illusions affecting audition.

Rubber hand illusion
In the rubber hand illusion (RHI), human participants view a dummy hand being stroked with a paintbrush, while they feel a series of identical brushstrokes applied to their own hand, which is hidden from view. If this visual and tactile information is applied synchronously, and if the visual appearance and position of the dummy hand is similar to one’s own hand, then people may feel that the touches on their own hand are coming from the dummy hand, and even that the dummy hand is, in some way, their own hand. This is an early form of body transfer illusion. The RHI is an illusion of vision, touch, and posture (proprioception), but a similar illusion can also be induced with touch and proprioception. The very first report of this kind of illusion may have been as early as 1937.

Body transfer illusion
Body transfer illusion involves the use of typically, virtual reality devices to induce the illusion in the subject that the body of another person or being is the subject’s own body.

Question 51

Real-world application:

Why do we care about all these details?

Answer 51

Bionic Eye Cures Blindness

Question 52

Retina & LGN

Answer 52

Receptive fields:

Center-­‐surround organizati?on

Question 53

Why have surround inhibition?

Answer 53

-­ Sharpens contrast
-­ Edge detection
‐ Fundamental principle of perception:
Brain cares about change

Question 54

Cortical Visual Areas: V1

Answer 54

V1 likes oriented lines

Hubel & Wiesel

Question 55

Cortical Visual Areas:

V4

Answer 55

V4 likes color, shapes;

attention

Question 56

Cortical Visual Areas:

MT

Answer 56

MT likes motion

MT=V5

Question 57

Akinetopsia:

Answer 57

Motion-­‐Blindness

Question 58

Rods

Answer 58

– Sensitive to low-‐levels of light (night
vision)
– Higher density in periphery

Question 59

Cones

Answer 59

– Color & high acuity
– 3 types: Sensitive to different wavelengths of light
– Perception of “color” is based on ratio of activated cones (color opponency)
– Highest density in fovea

Question 60

Color-­‐Blindness

Answer 60

Color blindness, or color vision deficiency, is the inability or decreased ability to see color, or perceive color differences, under normal lighting conditions. Color blindness affects a significant percentage of the population. There is no actual blindness, but there is a deficiency of color vision. The most usual cause is a fault in the development of one or more sets of retinal cones that perceive color in light and transmit that information to the optic nerve. This type of color blindness is usually a sex-linked condition. The genes that produce photopigments are carried on the X chromosome; if some of these genes are missing or damaged, color blindness will be expressed in males with a higher probability than in females because males only have one X chromosome (in females, a functional gene on only one of the two X chromosomes is sufficient to yield the needed photopigments).

Question 61

Achromatopsia:

Answer 61

True color blindness (typically cortical lesion)

Patients can only see in shades of grey

Question 62

Dichromats

Answer 62

Occurs when there are only 2 types of cones in retina.
-­ Typically missing red or green: can’t tell the difference between red/green (all look yellowish)
‐ Can still use luminance differences
‐ Genetic
(8% males, 1% females)

Question 63

Adaptation/Aftereffects

Answer 63

• Fundamental principle of perception
– Fatigue one type of neurons (e.g., “red”)
– Then present neutral stimulus
– Perception is biased in opposite
direction
(“red” cells too ?red, so visual system tricked into thinking blank screen is more green)
– Works for motion,
orientation, face gender, etc
– Other senses experience this phenomenon too

Question 64

Visual Cognitive Functions

Answer 64

• Spatial localization
• Detection/discrimination
• Object recognition
• Color/texture
• Motion cues
• Depth perception
• Navigation

Question 65

Visual

Illusions

Answer 65

The brain is tuned to relative differences

remember, neural systems like change

Question 66

Cogni?ve
Neuroscience
of
Illusions

Answer 66

• Which parts of the brain respond to what is seen?
Which parts respond to what is perceived?

• Can brain activity predict whether/when someone will see an illusion?

Question 67

Multimotion

Answer 67

• Multisensory areas:
STS (temporal), parietal, frontal, superiorcolliculus
• Weak responses can sum together
• Spatial/temporal synchrony important
– E.g., lip reading

Question 68

Multimodal

Illusions Example

Answer 68

McGurk

Effect

Question 69

Synesthesia

Answer 69

Mixing of 2 senses
– E.g., Colored letters
– Real effect

• Can do objective experiments (e.g, Stroop)
– ~1/23
people; some genetic basis

Question 70

The McGurk Effect

Answer 70

The McGurk effect (named after Harry McGurk, 1976) demonstrates how we use visual speech information. The effect shows that we can’t help but integrate visual speech into what we ‘hear’.

You see and hear a mouth speaking 4 syllables. Watch the mouth closely, but concentrate on what you’re hearing. Watch many times to be sure of the syllables you hear. After you feel certain of what you perceive, stop the movie.

Now start the movie again and close your eyes. Listen to the movie repeat until you are sure of what you hear. When you feel certain of what you hear, stop the movie and continue.

If you’re like most people, what you hear depends on whether your eyes are opened or closed.

How the stimuli were made: These stimuli were made by dubbing a single repeated audio syllable onto 4 different visual syllables.
Depending on the audiovisual syllable combination used:
-the visual syllable can overide the auditory syllable to determine what we perceive
-the auditory and visual syllables can combine to produce a new perceived syllable
-the auditory syllable can overide the visual syllable to determine what we perceive

What the effect means: The McGurk effect shows that visual articulatory information is integrated into our perception of speech automatically and unconsciously. The syllable that we perceive depends on the strength of the auditory and visual information, and whether some compromise can be achieved. Regardless, integration of the discrepant audiovisual speech syllables is effortless and mandatory. Our speech function makes use of all types of relevant information, regardless of the modality. In fact, there is some evidence that the brain treats visual speech information as if it is auditory speech .

How general is the McGurk effect?
The effect works on perceivers with all language backgrounds.
The effect works on young infants.
The effect works when the visual and auditory components are from speakers of different genders.
The effect works with highly reduced face images.
The effect works when observers are unaware that they are looking at a face.
The effect works when observers touch—rather than look—at the face.
The effect works less well with vowels than consonants.
The effect works less well with nonspeech pluck & bow stimuli (Saldaña & Rosenblum, 1994).
The effect works better with some consonant combinations than others.

To produce a demonstration of the McGurk effect: (you’ll need two other people besides yourself)

1) have an observer face you and keep looking at your face
2) have another person stand behind you so the observer can’t see their face
3) starting synchronously, repeatedly mouth the word ‘vase’ (silently) while the person behind you repeats the word ‘base’ out loud -you can achieve synchronization by counting down ‘3, 2, 1. . vase, vase, vase, etc
4) after about 8 repetitions, stop and ask the observer what they ‘hear’ -they should ‘hear’ vase
5) now do the same thing, and this time tell the observer to shut their eyes after a few repetitions
6) they should hear ‘base’ with their eyes shut
7) the observer can try opening and shutting their eyes, and what they ‘hear’ should change from ‘vase’ to ‘base’

Some tips on making your own McGurk Stimuli: Audiovisual dubbing can be achieved by using two videotape players or digitizing stimuli onto a computer and using software to mix the audio and video components. The quality of the auditory channel should be good, but the quality of the visual channel can be fair without much loss in the effect. The auditory and visual components should be synchronized so that the sound of the syllable seems to be coming from the visible mouth. However, the components do not have to be perfectly synchronized for the effect to work. The syllable combinations used in the demonstration are known to be especially strong.

Question 71

Contralateral Representation

Answer 71

Vision

Somatosensory