The human body is amazing

 Sensation & Perception

Fall 2015

Final topics list

As a general note, the exam will have several questions which will require you to consider similarities or differences among the senses. So while studying, make sure to make comparisons. For example, we talked about how distributed coding in olfaction is similar to trichromatic theory in vision. 

You will be asked to select one diagram from 4 choices for labeling and description. 

Also, pick TWO illusions from perception (from ANY sense) for which you can explain the underlying physiological mechanisms (hint, hint). For example, the Ponzo illusion, afterimages, the Buddha with the growing belly…

Basics

How we measure perception in the lab 

Method of limits • Stimuli of different intensities presented in ascending and descending order • Observer determines whether the shaded bright patch is brighter or dimmer than the unshaded bright patch. • Cross-over point is the threshold

Constant Method of constant stimuli • 5 to 9 lights (stimuli )of different intensities are presented in random order • Subject forced to choose which patch looks brighter. • Multiple trials are presented • A perceptual light is the intensity that results in in 50% of trials seen as brighter. 

Adjustment Method of adjustment • Intensity of the stimuli is adjusted continuously the participant control the stimuli 

Weber’s law

Absolute threshold

% ABSOLUTE THRESHOLD: The minimum intensity of stimulation (brightness of a light; loudness of a tone) required to produce a detectable sensory experience

DIFFERENCE THRESHOLD: The minimum change in intensity required to produce a detectable change in sensory experience (this is also known as a Just Noticeable Difference or JND) Thresholds: two types Figure

How

Label a neuron

How do neurons communicate?

Neurons communicate over long distances by sending signals called nerve impulses through the axons which make up a tract or nerve. Because each axon may branch into a whole tree, and because nerve impulses go down each branch when an axon divides, a single neuron may send signals to thousands of other neurons. Meanwhile, the dendrites and cell body (and often the axon) of that single neuron may receive nerve impulses from thousands of other neurons. So the nervous system is one big network of neurons, with each cell having inputs and outputs that may connect it to thousands of other nerve cells. thenThe output from an axon arrives at an area called a synapse (a nerve impulse reaches the end of an axon, it stimulates chemicals called transmitters or neurotransmitters to flow rapidly across the synaptic cleft, producing an output from the axon and an input on the dendrite of the following neuron. Each neuron might stimulate thousands of other neurons this way.

How is each neuron like a pattern recognizer?When transmitters flow across a chemical synapse, they have one of two effects on the post-synaptic neuron (the neuron that comes after the synapse). They either excite it (make it more likely to fire a nerve impulse itself) or inhibit it (make it less likely to fire a nerve impulse itself). Each neuron responds to many such inputs and, based on the pattern of activity and how recently it has fired an impulse, either fires another nerve impulse or not. In that sense, each neuron is like a pattern recognizer, responding to the pattern of inputs (and timing of inputs) from other cells. One neuron might fire when you smell garlic, another might fire when you see a familiar face, or have a particular memory, and so forth. The overall pattern of firing in the nervous system determines your state of mind, moment by moment. Most of this activity is unconscious, but some small part of it composes your conscious thought process. "That art thou."

  and inhibition are result of action potentials cells become positively charged Excitation or negatively charged axon then there are other gates that are sensitive to the increase of charge so opens gates and more sodium flushes in in a constant chain of opening gates of sodium.

Action potential is a moving charge.

Myelin (fatty acid ) wraps itself around the axon and blocking the flow of sodium myelin then increases the speed of the action potential

Sodium potassium pump: removes using energy sodium from inside of the axon to the outside of the axon. In exchange it takes a potassium ion inside.

Neurons can go through refractory period when they are not quite reset yet there is a limit on how quickly you can send of action potentials. Firing rate for the action potential that firing rate can be part of the message neuron can have a low firing rate kind of important small information if it is high firing rate that means the neuron has received a lot of information.

Simple synapse where one axon terminal is lined up with a dendrite

synaptic gap is space between axon terminal and dendrite

when you open the gate you get influx of ion

two types 

excitatory influx: positive charge raise charge of neuron -70 towards 0mV

“depolarize” opens receptors that allows for positive neurons

inhibitory influx: negative ions (chloride) -70 further away towards -100 mV

“hyperpolarize” opens receptors that allows for negative neurons

Specificity coding is when each neuron had a preference for a particular stimuli and is activated by that particular stimulus.

distributed coding you look at the different patterns of activated neurons which identifies the stimulus

Areas of the brain and relation to the senses

Temporal lobe is involved in hearing (has some vision)

Occipital drives vision

The Parietal lobe works on touch(as well as vision)

Frontal lobe does taste and smell(olfactory)

Vision, part 1

Label an eye

cornea: initial bend of light as it comes into eye. (adjust when you get laser surgery on the eye) (80 percent focusing)

Iris: actually a muscle expands and contracts 

Pupil: is a hole in the middle of the iris. Size of pupil depends on the expansion and contraction of the iris. This lets in more light or less light.

Lens: Focus the light. This has muscles called the ciliary muscles they can make the lens fatter or they can stretch the lens and make it thinner.(fine adjustments last 20 percent of focusing)

Vitreous humor: main chamber of the eye, keep shape of the eye (jelly like substance) cleaning the eye

Aqueous humor: cleans eyes as well

Retina: where your actual transduction occurs, rods and cones are present here.

Fovea has a high density of cones this is where we get are highest acuity happens in the fovea. This is where are lens is trying to focus the light.

Blind Spot: Nerve or bundle of axons leaving the eye there’s no space for rods and cones there you cannot have vision here hence the name.

Optic nerve: is bundle of axons from retina leaving the eye to go to the brain.

9 

Convergence and how it relates to acuity (pgs 58-61)

Convergence: is combining the input from multiple receptors. The more input a bipolar cell receives its response is going to change.

Rods converging we get similar output. Because of convergence we lose special pattern of the light.

Cones with there own bipolar cells we retain the pattern.

Cones that receive from one bipolar cell are called (midget)

Bipolar cells receiving from multiple sources is call (diffuse).

Vision, part 2

Feature detectors

Simple cortical cells: have an orientation bias/tuning can be up, down, diagonal, horizontal,, can find which preference it wants

Complex cortical cell have orientation bias, but prefers that line to be moving in particular direction (movement)

End stopped cells-prefer an angle or an end, try to find corners, intersections of two lines.

Orientation tuning curves

Tuning curves are widely used to characterize the responses of sensory neurons to external stimuli Selective rearing / experience dependent plasticity

What vs. where pathway

Dorsal is the where pathway

Ventral stream is what pathway.

Object task looking for particular shape

Landmark task the monkey is trying to find the well closest to a particular landmark. Just want to know if its closer to food well then other side.

Temporal lobe lesion no longer able to object task but still do the landmark task.

Parietal lobe they are able to do object task but are no longer able to do landmark task.

Temporal lobe tells us what things are

Parietal lobe where things are.

Object Agnosia: difficult time in object recognition 

Object Recognition

Objects do not always look the same 

Concepts that have multiple shapes

We are inconsistent on how we see shapes

Inverse projection problem-one image on retina could be made by multiple possibilities out in the world.figuring out what a 3d image is on a 2d retina 

Viewpoint invariance your viewpoint is different but recognize the same object from multiple angles

Recognition-by-components theory

We recognize object through the breaking down of an object into components(component parts =geons) parts that are easy to recognize at any angle

Color

Trichromatic theory

The theory that we need three different color cones to see color (red,blue,green)red is long wave length, blue is short wave length and green is medium we need the interaction of these three cones to see all colors 

Understand the color spectrum and what colors are where!

Hue is the amount of color you actually see in the fovea from wavelength produced by color(light)

Saturation is the amount of color you see 

Brightness the amount of light seen 

Depth

How we see 3d objects from a 2d retina

Monocular depth cues

Occulusion: when object is covering another object it give s us the relative distance which states that object coving the other object must be closer.

Relative size: comparing sizes of similar objects that should be similar, so if one of the objects appears to be smaller we know that the object is further away. Example we take a photo of two bears that are the same size but in looking at the photo one bear looks smaller therefore know they are the same size you the know the smaller bear is father away.

Texture gradient: looking at closeness of objects similar sized and equal spaced

Relative height: looking at the base of the object in your fielf of view the base that is higher is further away. Example (ames room)

Relative to horizon: the closer to the horizon the object is the further away the object is.

Linear perspective: lines look to go together as they go further out.

Shadow the bigger the shadow the futher away the object is from the ground

The horopter

When things fall on the horopter they have corresponding points on the retina 

Motion

Corollary discharge theory

Hearing

The mechanisms behind sound transduction

In the auditory system, sound vibrations (mechanical energy) are transduced into electrical energy by hair cells in the inner ear. Sound vibrations from an object cause vibrations in air molecules, which in turn, vibrate your ear drum. After ear drum activate4s malleus and stapes which opens the oval window where it is transform into liquid form into sound wave which goes through scala typami and goes to apex then to scala vestibule out round window

Tonotopic map in hearing high frequently       

Sound localization

ITD and ILD 🡪 NOTE!!! Neither gives you elevation information! Auditory Localization; the ‘Where’ pathway for the auditory system • Auditory space - surrounds an observer and exists wherever there is sound • Researchers study how sounds are localized in space by using – Azimuth coordinates - position left to right – Elevation coordinates - position up and down – Distance coordinates - position from observer Auditory Localization • On average, people can localize sounds – Directly in front of them most accurately – To the sides and behind their heads least accurately Location cues are not contained in the receptor cells like on the retina in vision; location for sounds must be calculated through other cues. 3 primary cues for auditory localization: 1. Interaural time difference (ITD) 2. I nteraural level difference (ILD) 3. Head-related transfer function (HRTF) Cues for Auditory Location • Binaural cues - location cues based on the comparison of the signals received by the left and right ears Cue 1: Interaural time difference (ITD) - difference between the times sounds reach the two ears • When distance to each ear is the same, there are no differences in time • When the source is to the side of the observer, the times will differ 0 1 2 3 4 Left 0 1 2 3 4 Right Time (msec) 0 1 2 3 4 Left 0 1 2 3 4 Right Time (msec) Interaural time difference (ITD) Speed of sound at sea level: 761 mph = 6.22 inches/millisecond It should take about 0.6 msec for sound to travel the width of the average head. ITD for different directions: Interaural time difference (ITD) The ‘Cone of Confusion’: Set of locations that have the same interaural time differences (ITD)

How you figure out elevation information

The azimuth is the angle between the north vector and the perpendicular projection of the star down onto the horizon. Azimuth is usually measured in degrees (°).

Vestibular

The otolith organs

They are utricle and saccule they are for linear acceleration

Touch

The different mechanoreceptors\

 mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. Normally there are four main types in glabrous skin: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini endings. There are also mechanoreceptors in hairy skin, and the hair cells in the cochlea are the most sensitive mechanoreceptors, transducing air pressure waves into nerve signals sent to the brain. In the periodontal ligament, there are some mechanoreceptors, which allow the jaw to relax when biting down on hard objects; the mesencephalic nucleus is responsible for this reflex.

Although the anatomical research on the human mechanoreceptors started with the discovery of Vater-Pacinian corpuscle in early 18th century,[1] the electrophysiological research into the mechanoreceptors of the human body began in the mid of 20th century, when Vallbo and Johansson took percutaneous recordings of human volunteers.[2] The mechanoreceptors of primates like rhesus monkeys and other mammals are similar to those of humans and also studied even in early 20th century anatomically and neurophysiologically.[3]

Contents

  [hide] 

1Mechanism of sensation

1.1Feedback

2Types

2.1Cutaneous

2.1.1By sensation

2.1.2By rate of adaptation

2.1.3Receptive field

2.2Others

2.2.1Ligamentous

3Lamellar corpuscle

4Muscle spindles and the stretch reflex

5See also

6Notes

7External links

Mechanism of sensation[edit]

In somatosensory transduction, the afferent neurons transmit messages through synapses in the dorsal column nuclei, where second-order neurons send the signal to the thalamus and synapse with third-order neurons in the ventrobasal complex. The third-order neurons then send the signal to the somatosensory cortex.

Feedback[edit]

More recent work has expanded the role of the cutaneous mechanoreceptors for feedback in fine motor control.[4] Single action potentials from Meissner's corpuscle, Pacinian corpuscle and Ruffini ending afferents are directly linked to muscle activation, whereasMerkel cell-neurite complex activation does not trigger muscle activity.[5]

Types[edit]

Tactile receptors.

In glabrous (hairless) skin, there are four principal types of mechanoreceptors, each shaped according to its function. The tactile corpuscles (also known as Meissner corpuscles) respond to light touch, and adapt rapidly to changes in texture (vibrations around 50 Hz). The bulbous corpuscles (also known as Ruffini endings) detect tension deep in the skin and fascia. The Merkel nerve endings (also known as Merkel discs) detect sustained pressure. The lamellar corpuscles (also known as Pacinian corpuscles) in the skin and fascia detect rapid vibrations (of about 200–300 Hz).

Receptors in hair follicles sense when a hair changes position. Indeed, the most sensitive mechanoreceptors in humans are the follicular receptors for the hair cells in the cochlea of the inner ear; these receptors transducesound for the brain.

Mechanoreceiving free nerve endings detect touch, pressure, and stretching.

Baroreceptors are a type of mechanoreceptor sensory neuron that is excited by stretch of the blood vessel.

Cutaneous[edit]

Cutaneous mechanoreceptors respond to mechanical stimuli that result from physical interaction, including pressure and vibration. They are located in the skin, like other cutaneous receptors. They are all innervated by Aβ fibers, except the mechanorecepting free nerve endings, which are innervated by Aδ fibers. Cutaneous mechanoreceptors can be categorized by morphology, by what kind of sensation they perceive, and by the rate of adaptation. Furthermore, each has a different receptive field.

The Slowly Adapting type 1 (SA1) mechanoreceptor, with the Merkel cell end-organ, underlies the perception of form and roughness on the skin.[6] They have small receptive fields and produce sustained responses to static stimulation.

The Slowly Adapting type 2 (SA2) mechanoreceptors respond to skin stretch, but have not been closely linked to either proprioceptive or mechanoreceptive roles in perception.[7] They also produce sustained responses to static stimulation, but have large receptive fields.

The Rapidly Adapting (RA) mechanoreceptor underlies the perception of flutter[8] and slip on the skin.[9] They have small receptive fields and produce transient responses to the onset and offset of stimulation.

The Pacinian corpuscle or Vater-Pacinian corpuscles or Lamellar corpuscles [10] underlie the perception of high frequency vibration.[8][11] They also produce transient responses, but have large receptive fields.

By sensation[edit]

Further information: Cutaneous receptor modalities

By rate of adaptation[edit]

Cutaneous mechanoreceptors can also be separated into categories based on their rates of adaptation. When a mechanoreceptor receives a stimulus, it begins to fire impulses or action potentials at an elevated frequency (the stronger the stimulus, the higher the frequency). The cell, however, will soon "adapt" to a constant or static stimulus, and the pulses will subside to a normal rate. Receptors that adapt quickly (i.e. quickly return to a normal pulse rate) are referred to as "phasic". Those receptors that are slow to return to their normal firing rate are called "tonic". Phasic mechanoreceptors are useful in sensing such things as texture or vibrations, whereas tonic receptors are useful for temperature and proprioception among others.

Slowly adapting: Slowly adapting mechanoreceptors include Merkel and Ruffini corpuscle end-organs, and some free nerve endings.

Slowly adapting type I mechanoreceptors have multiple Merkel corpuscle end-organs.

Slowly adapting type II mechanoreceptors have single Ruffini corpuscle end-organs.

Intermediate adapting: Some free nerve endings are intermediate adapting.

Rapidly adapting: Rapidly adapting mechanoreceptors include Meissner corpuscle end-organs, Pacinian corpuscle end-organs, hair follicle receptors and some free nerve endings.

Rapidly adapting type I mechanoreceptors have multiple Meissner corpuscle end-organs.

Rapidly adapting type II mechanoreceptors (usually called Pacinian) have single Pacinian corpuscle end-organs.

Receptive field[edit]

Cutaneous mechanoreceptors with small, accurate receptive fields are found in areas needing accurate taction (e.g. the fingertips). In the fingertips and lips, innervation density of slowly adapting type I and rapidly adapting type I mechanoreceptors are greatly increased. These two types of mechanoreceptors have small discrete receptive fields and are thought to underlie most low-threshold use of the fingers in assessing texture, surface slip, and flutter. Mechanoreceptors found in areas of the body with less tactile acuity tend to have larger receptive fields.

Taste/smell

Neural coding behind smell perception

Different odorants and fit into to different receptors

How are odors different than other stimuli? Based upon memory and previous exposure