LO7 - Sensation and Perception 2

Question 1

Sound

Answer 1

This is an external energy/force in the form of vibrations through a medium (air/water) that cause pressures changes or waves.

Question 2

Frequency (sound)

Answer 2

For sound, the number of times per second that a pattern or pressure repeats (number of oscillations) is the frequency. This is perceived as pitch.

Pitch is a psychological aspect that we perceive.

Question 3

Amplitude/Intensity (sound)

Answer 3

The magnitude of displacement (increase or decrease) of a sound pressure wave is the amplitude.

It is perceived as loudness/intensity. Higher waves = louder sounds.

Question 4

The Ear

Answer 4

The ear collects sound energy and transforms it into neural signals.

Question 5

Outer ear

Answer 5

The Pinnacle is the outer segment of the ear - it is shaped to collect and funnel sound towards the tympanic membrane.

The tympanic membrane (AKA ear drum) transfers sound energy from the air to the ossicles. Vibrations are sent to your middle ear.

It is a thin sheet of skin that moves in and out responding to the pressure changes of sound waves.

Question 6

The middle ear

Answer 6

The main role of the middle ear is to amplify the signal collected.

Ossicles are found in here and there are three kinds. They are small bones that amplify sound arriving at the ear drum to the oval window of the cochlea.

Question 7

Ossicles - Malleus, incus and stapes

Answer 7

Malleus is connected to the tympanic membrane.

Incus is connected to the malleus

Stapes is connected to the incus

They are all small bones that act as a lever and move in response to the signals picked up and send these to the inner ear.

This magnify so the signal by 18X which is enough energy to send signals through the fluid filled membrane of the cochlea.

Question 8

Inner Ear - The Cochlea

Answer 8

The cochlea is a fluid-filled, coiled structure. Within it there are two membranes that create three canals.

It is in the cochlea where fine changes in sound pressure and translated into neural signals.

The transduction of sound waves occurs in these membranes.

Question 9

Basiliar membrane

Answer 9

This is the most important membrane in the cochlea. It is where the hair cells are location and these transduce sound waves.

Question 10

Tectorial membrane

Answer 10

This floats above the basiliar membrane and connects to the hair cells. It moves in response to fluid vibration.

Question 11

Hair cells

Answer 11

These are the equivalent of photoreceptors but in the ear. They transduce mechanical movement from sound waves into neural activity.

Fluid vibrations from sound casus the basilar membrane to move (ripple).

This movement causes the cilia of the hair cells to bend. This bending causes a neural signal to be sent down the auditory nerve (action potential fires)

Question 12

Structure of hair cells

Answer 12

Hair cells are connected to the tectorial membrane with finger-like structures (cilia). When fluid vibrations come through the cochlea they cause a slight displacement of the membranes.

It is this wobble that sends a neural signal.

They are sometimes called mechanoreceptors as they bend which causes action potentials to fire.

Question 13

Two theories of how it is possible to hear differences in frequency of sound:

Answer 13

Place theory and frequency theory.

As there is only one type of hair cell, there must be some way that we interpret different frequencies.

Question 14

Interpreting sound - place theory

Answer 14

The brain uses the location of the neural firing to understand sound.

Different frequencies/intensities will travel different lengths along the cochlea. High frequencies are better tuned to the base and low frequencies travel further.

Location indicates pitch

Question 15

Interpreting sound - Frequency theory

Answer 15

The brain uses information related to the rate of cells firing. The more rapidly the cells fire, the higher the perception of the pitch.

Additional information codes pitch perception. The rate of sound wave frequency corresponds to a pulse rate that matches the frequency of the sound you are hearing.

Action potentials are sent at a matching rate/frequency and the brain uses this information to interpret pitch

Question 16

Issue with place theory of interpreting sound

Answer 16

In order for a low frequency to reach the end of the cochlea, it travels all the way along and activates all the hair cells along the way.

You would expect them to interpret high frequencies as well.

Question 17

Auditory pathway

Answer 17

Axons send signals through the auditory nerve. Auditory information travels to medial geniculate nucleus of thalamus.

The thalamus is the sensory relay centre

Auditory cortex is located in the temporal lobe.

Question 18

Tonotopic organisation

Answer 18

The spatial organisation of the basilar membrane is maintained through the auditory pathway.

We have persevered the spatial organisation. Frequencies that correspond to places along the cochlea are similarly mapped onto the auditory cortex.

Question 19

Sound localisation

Answer 19

Detection of an objects location in space relies on binaural cues (auditory cues that require comparisons from both ears)

Question 20

Interaural time differences

Answer 20

Differences in arrival times of auditory cues to each each. Helps in sound localisation.

Question 21

Interaural level differences

Answer 21

Differences in the intensity of the sounds that reach each ear help in sound localisation.

One ear may hear the sound shadow which proves that the sound is coming from the other direction.

Question 22

Sound perception (phantom words)

Answer 22

Ambiguous words can be heard differently by all. From the same stimulus we get different perceptions. Our brains are not perfect interpreters

What we hear is shaped by our prior knowledge. This is top-down processing.

What is the mechanism that transforms sound to meaningful words? This could tell us both about normal perception but also when it goes wrong (schizophrenia)

Question 23

Touch

Answer 23

This is pressure against skin/tactile sensations. The main organ is the skin but it includes other epithelial lining.

We can detect mechanical interactions, temperature and pain.

Question 24

Mechanoreceptors

Answer 24

These transduce mechanical stimulation into touch sensation by creating neural signals.

We have a variety or ways of detecting external force in our skin.

Question 25

Merkel receptor (type of mechanoreceptor)

Answer 25

These detect the application and removal of pressure. They fire constantly while pressure is being applied meaning it is constantly sending a signal.

It will stop when pressure is removed.

They work together with Meissner corpuscle mechanoreceptors.

Question 26

Meissner Corpuscle (type of mechanoreceptor)

Answer 26

Responds to the application and removal of pressure. It fires when there is a change in pressure.

I.e. while pressure is being applied and while it is being removed.

Question 27

Ruffini cylinder (type of mechanoreceptor)

Answer 27

Interprets stretch of skin.

Orientation helps this.

Question 28

Pacinian corpuscle

Answer 28

Responds to vibration and texture.

They don’t respond to external pressure as they are found deeper and have a wider receptive field.

Question 29

Thermoreceptors

Answer 29

These are sensory receptors that signal information about changes in skin temperature.

They are free nerve ending with two distinct populations: warmth and cold fibres.

They also respond to chemical stimuli which is why when you eat chilli it feels hot and when you eat menthol it feels cold.

It is not entirely known how thermoreceptors transduce heat into a neural signal.

Question 30

Nociceptors

Answer 30

Sensory receptors that transmit information about noxious/painful stimuli that causes damage or potential damage to skin.

They detect when a stimuli reaches a maximum threshold. They start firing at this point.

Question 31

Somatosensory cortex

Answer 31

Information gets relayed from periphery nerves to the thalamus and then to the contralateral parietal lobe.

Question 32

Somatotopic organisation

Answer 32

The somatosensory cortex is spatially mapped in correspondence to spatial events on the skin.

Adjacent points on the skin are represented by adjacent points on the somatosensory cortex.

It is not a perfect representation and some areas have more cortex dedicated to them to others.

Question 33

Distribution of mechanoreceptors

Answer 33

Our body is disproportionately distributed with mechanoreceptors. We have most in our face and hands.

It is evolutionary as we use our hands a lot.

Question 34

Body schema modifications

Answer 34

Visual inputs integrate with and can even override our conscious body image. It is not just sensory receptors that feed into our schema/understanding of your body.

You can adopt a rubber hand as your own and flinch when it is hit.

Question 35

Multi-sensory perception

Answer 35

This influences how we see our own body. The brain changes in response to experience (plasticity) and can rewire itself to see something as part of our own body.

Visual information infiltrates our perception of ourselves.

Question 36

Tools being integrated into body schema

Answer 36

Macaque monkeys are trained to use a rake to receive a food reward. After training, recording from the somatosensory cortex shows that cells that typically responds to hand visual receptive field not incorporated the rake.

The tool was incorporated into the body schema. We can see this in humans as we have enlarged our conscious body image to include our phones.

However, those with backpacks are not aware of it because we cannot see them.

Question 37

Narrative

Answer 37

Our brains have a natural tendency to find meaningful patterns and causality in our surrounding world.

We not only combine prior knowledge to perceive something but we also assign a deterministic cause for what we perceive.

This is more of a metaperception than a classical perception.

It provides meaning to what we take in. We give an action a reason for why it has occurred.

Question 38

Attribution of causality

Answer 38

Humans have a natural tendency to attribute causality to situations we see.

Question 39

Attribution of causality - Heider-Simmel 1944

Answer 39

He gave participants a video with shapes and then asked questions about them as if they were characters.

You automatically assign characters, a setting and a narrative to inanimate, moving shapes.

Question 40

All-encompassing narrative

Answer 40

We tend to find patterns/narrative that explain all variables and this seems to be a form of adult human perception.

Red light/ blue light experiment involves guessing which light will flash - it is probability guessing. Lights are rigged so that 80% is blue and only 20% is red.

Children and rates will maximise and are 80% correct by always guessing blue.

Adult humans will frequency match and are around 67% correct.

Maximising is choosing the option that occurred the most frequently in the past.

Frequency matching is incorporating the frequency of all previous occurrences with the current guesses. It looks to fit every piece of evidence into an all encompassing story/perfect pattern.

Question 41

Narrative in the brain - split brain patients

Answer 41

Corpus callosum has been severed so communication between the left and right hemispheres is impaired.

Because hemispheres are fairly specialised, in split brain patients, two independent forms of knowledge exist.

The left hemisphere is critical for language comprehension and formation.

You may perceive something on the right but it is sent to the left for processing if related to language.

Question 42

Split brain studies

Answer 42

If a split brain patient sees an object in the right eye, this is projected to the left hemisphere and they are able to name the object.

If they see an object in their left eye, not only can they not name the object but they also have no recollection of seeing that object.

Patients choose the object shown to them out of a selection of different objects despite this. When asked why, they create a narrative to create causality.

Question 43

The interpreter

Answer 43

The neuro-psychological concept proposed by Gazzaniga to explain the narrative. It links to language centres.

Causal explanations are generated by the left-hemisphere. It combines already known knowledge with ongoing events to infer causation.

Thought to act post-hoc to events that we experience.

The interpreter is the left brain process which generates narrative.

Question 44

fMRI activity of participants listening to an auditory story.

Answer 44

Red/Yellow/Green is shown when the narrative is scrambled.

Blue is shown when there is a coherent narrative and not the sensory modality.

Blue areas overlap with the Default Mode Network (DMN) which is proposed to provide situation models: representations that link entities, actions and outcomes.

This is the area activated when daydreaming.

Question 45

From perception to memory

Answer 45

Participants watch a movie in an fMRI scanner then recall the story immediately afterwards.

There is synchrony in spatial brain activity across participants whilst watching the same movie.
There is synchrony in spatial brain activity within a single participant between watching the movie and verbally recalling.

The greatest synchrony occurs between participants during the recall session. This makes little sense so we must have some mechanisms that narrows down our perceptions of narratives to create similar narratives

Is this innate or cultural? Consistency in folk laws across cultures suggests that certain narratives fit well with our understanding of the world