NEUR1020 - MODULE QUIZ 2

what is a sensory adaptation

when, after prolonged exposure to sensory inputs, people experience an aftereffect

adaptation happens in all sensory modalities and it can have similar effects

helps to ensure perception is useful but it isn’t accurate

what is the motion aftereffect

when the sensory aftereffects are the opposite experience relative to the adaptor

what causes aftereffects

aftereffects are associated with reduced responding in the brain to the adapted input. This can enhance the salience of new inputs relative to old inputs because the brain in more responsive to new inputs 

what is troxler fading

• whenever we stare at a static screen - a physically identical disc will look brighter compared to the other disc on the screen

• this is a visual adaptation

what suggests we do not have veridical experiences of sensory input

• perceptual aftereffects

• our experiences are a product of activity in our brains, and that activity can promote experiences that differ from sensory input

• our brains tend to create perceptual experiences that sum together all the sensory information that is available to use

what is the McGurk effect

• a play on auditory perception where you hear something different when the voice is accommodated by visual lip movement

• shows that people do not have veridical sense of input from any single sensory modality

what is perception

• our brain’s running hypothesis about what is out there in the real world based on analyses of the evidence promoted by our sense organs 

how does the brain transduce environmental signals to our brain for audition

1. the transformation of sound waves (vibrations) through a medium (often air) into signals that can be sent to the brain

2. the hair cells in the cochlea of our inner ears transforms this energy into signals for our brain

how do soundwaves work

• sound waves alternate in exerting increased or decreased pressure on air molecules

• these alterations in air pressure are described as waves and have two important characteristics

what are the two characteristics of sound waves

1. frequency → how often air pressure is increased then decreased over time (controls pitch)

2. amplitude → the magnitude of changes in air pressure (controls the loudness of the sound) → big changes create loud sound and vice versa

how does our eyes transduce light into signals for the brain

1. photoreceptors which form the retinae of the human eyes 

explain the importance of the pigment positioning in photoreceptors and the arrangement of the eye

• the pigments in the photoreceptors are positioned at the back of the retinae, away from the light. This limits the human eye, as light must pass through a number of cellular layers before reaching the photoreceptors

• the arrangement of the eye also dictates that the optic nerve must pass through the surface of the retina.

what is the physiological blind spot

• the place where the optic nerve passes through the retina. There are no photoreceptors so you are blind to any image that falls onto this region of the retina

what is perceptual filling in

when the brain seems to assume that what is on either side of the blind spot is also within the blind spot.

• shown in the unbroken bar test → you perceive an unbroken bar that extends right across your blind spot

• also shown in neon colour spreading

what does perceptual filling in demonstrate

• human vision is a construction of what the brain infers is probably present

what is naive realism

when you believe you have veridical impressions of the images that reach your retinae (ie. duck-rabbit illusion)

what are colours associated with

• the colours we experience are associated with different wavelengths of light. This is determined by the range of wavelengths of light the photoreceptors can absorb

• colour vision also relies on the number of different types of photoreceptors we have in our retinae

what is humans range of wavelengths of light

• between 400mm (blue) to 700mm (red)

what colours can birds see

• most birds can detect lower wavelengths and so they can see ultraviolet colours that we cannot detect

what are the different types of photoreceptors humans have

1. short cones (absorbs 430nm max)

2. medium cones (absorbs 530nm max)

3. long cones (absorbs 570 max)

humans have three cones and so are called trichromats

what is the basis of colour vision

• our ability to detect the ratio of activation across our three classes of photoreceptors

why is colour vision different for humans and animals

• colour vision is different for people and animals that have a different number of photoreceptor types 

what is red/green colour blindness and why is it not common

• red/green colour blindness is when a person is missing a cone - so they are dichromats (like cats and dogs)

• this colour blindness is less common in females as the defective gene is carried on the X chromosome

why are people deficient in colour vision often unaware of it

• because we all learn colour by association 

how do we tell if a person is colour blind

• we can tell people are having different experiences of colour when they have different patterns of sensitivity to physical input

• in people with normal colour vision → we all have quite different idiosyncratic ratios of the three types of photoreceptors.

what is colour constancy

• physical objects refract a range of different wavelengths of light, and this range is impacted by lighting and illumination; therefore, our visual systems strive to subtract the impact of lighting away from our impressions of colour. 

• colour constancy is when in different conditions, the colour of the same wavelength of light look very different.

• the human brain facilitates a sense of colour constancy by estimating what the prevailing light source is and subtracting its influence from your impression of object colours

what is the difference between sensation and perception

• sensation is an ability to detect a sensory input. Your nervous system can detect many signals that you may never become aware of.

• perception is your subjective experiences of sensory input (ie. the feeling of red, or the experience of roughness on your skin as you brush a rough surface). perception is a dynamic construct of the brain

what are protanopes, deuteranopes, and tritanopes

protanopes are people missing l-cones, deuteranopes are people missing m-cones, and tritanopes are people missing s-cones. They are all more common in males than females.

what are coloured aftereffects

• coloured aftereffects is an example of the opponent process theory → after protracted viewing of certain colours, you can see oppositely coloured afterimages. Infer that the human visual system is contains competitive mechanisms tuned to opposite colours

• coloured aftereffects helped reveal what wavelengths of light cones are maximally responsive to

how can we module the response of cell inputs (sensory adaptation)

visual adaptation is one way to module the response of cells inputs. Attention is another → shown through the basketball demonstration

why do some people not notice their physiological blindspot

there are several reasons people don’t typically notice their blindspots. For example, the human visual system seems to assume that the same things that surround the blindspot are also within the blindspot → this is a process called perceptual filling in.

what is transduction

to see the visual system we must detect electromagnetic radiation and convert it into neural events. The conversion of electromagnetic radiation into neural events is called transduction. This involves light sensitive chemicals → visual pigments

what is the primary visual pathway

• signals leave your eye via the optic nerve travelling to the optic chiasm. Here signals cross, so information from either side of visual space crosses to one side of your brain regardless of which eye they come from

• signals from the right side of visual space travel to the left side of your brain

• signals from the left side of visual space travel to the right side of your brain

what does it mean if a problem is specific to information from one eye

• the problem must be in the eye itself, or in the optic nerve

what does it mean is a problem is specific to information from one side of visual space

• regardless of which eye you are looking with, the problem must be due to damage to the brain 

what is the primary visual cortex (V1)

• the first cortical region to receive visual signals along the primary visual pathway

• we have two V1s, one in each hemisphere of the brain

• each V1 responds to all visual inputs from one side of visual space. And adjacent neurons in V1 respond to input from adjacent positions on our retinas 

what is retinotopc

• the Russo/Japanese war brought about the first detailed mappings linking visual field deficits to localised damage in occipital brain regions

• the mappings of V1 responses. And all visual brain regions have retinotopically mapped responses

• these mapping of responses reflect which region of your visual field input has projected from

• retinotopic mapping is more apparent in lower level visual brain structures, where neurons are associated with small receptive fields.

• however we cannot see V1 activity as cells in V1 respond to inputs that we cannot see

what is cortical scotoma 

damage to either primary visual cortex → cannot see inputs that are usually encoded by the damaged region of V1

what is the flicker fusion threshold for colour

• describes how many times a second a light source can switch between different colours before we stop seeing flicker and start seeing a constant light source

• for humans this rate is about 30Hx

what is normal V1 activity necessary for

• normal conscious visual experiences. Without it people tend to report blindness

what is blindsight

• when some people think they are blind but actually are not. It can occur when people suffer damage to their V1

• sometimes V1 on one or both sides of the brain can be completely destroyed. In this case, people may report blindness to all visual input

what is perimetry

• the extent of blindness following damage to the visual system is quantified by a process called perimetry

what it the two-alternative forced choice task

• requires participants to guess even when they feel they cannot see an input

what did the monkey trial helen and patient O find

• performance without V1 is possible. We are able to navigate and avoid obstacles using vision despite insisting we cannot see

• blindsight shows that some visual operations can be carried out without activity in the V1

what issue does blindsight propose

• if we want a true measure of visual sensitivity, we cannot simply take people’s subjective opinion at face value

what is the signal detection theory

• describes how to measure sensory sensitivity in conditions of uncertainty, along with bias

• the hit rate is the proportion of times a participants reports seeing an input when it is actually presented

• the false alarm is the proportion of times a participants reports seeing an input when it was not presented

• this theory is also used in wider contexts such as finger print matches in crime scenes and airport security

what does is mean if the ration between hit rate and false alarm is 1

• the participant has displayed 0 sensitivity

• if a participant has any sensitivity, their hit rate should be greater than their false alarm rate

what two things do all visual neurons in the brain have

1. receptive field → positioned on retina so that images must fall upon to make that visual neuron respond

2. response selectivity → the type of input to which a cell will respond

what do cells in the V1 respond to

• in V1 cells still respond to fairly simple things (bars of light/colour). but these cells also project to other cortical regions which respond to increasingly complex properties (ie. patterns)

what is the architecture of the human vision and its characteristics 

1. specialisation → cells respond selectively to specific stimulus characteristics

2. modularity → cells that respond to similar stimulus characteristics are clustered into specific brain regions

3. a hierarchy of processing structures → cells that respond to progessively more complex stimulus characteristics as we follow the anatomical connections from the retina through to higher level visual brain regions

what doe V5, V4, and the occipital face area respond to

• V5 → patterns

• V4 → colour (not direction tuned)

• occipital face area → face

what is cerebral achromatopsia 

• bilateral damage to both V4s

• results in complete absence of colour vision

• if V4 on the left side of the brain is damaged, people can report colour blindness to input from the right side of visual space and vice versa

what is prosopagnosia 

• face blindness → seems to correlate with damage to the occipital face are

what is cerebral akinetopsia 

• without motion vision → it is rare as it can only be complete (ie. both V5s must be damaged)

what is functional modularity

• refers to the fact that our brains contain multiple regions that are specialised for processing different properties (ie. colour)

what is the binding problem

• the binding problem refers to the question whereby → how can the brain tell when activity spread across the brain is related to a common object?

• there are instances where the brain misbinds (Ie. steady state misbinding) features which only seems possible if there is a binding process that makes mistakes 

• there would be no binding problem if the brain did not have to combine activity from different brain regions to create perceptions

• the binding problem seems to be solved by an error prone process. Sometimes the wrong features are combined across space (steady state misbinding)

• and sometimes the wrong features are combined across time (colour motion perceptual asynchrony)

what are the different types of V1 cells and what are they responsive to

• simple V1 cells are responsive to oriented stripes of contrast located in a specific subfield of its RF

• end-stopped V1 cells are responsive to oriented stripes of contrast of a specific (limited) length

• complex V1 cells are responsive to oriented stripes of contrast located in a specific location

• complex direction-selective V1 cells are responsive to oriented stripes of contrast located anywhere within the RF but move in a specific direction

what is the dual visual streams theory

• the dual visual streams theory suggests that humans have two visual systems, one that promotes perception (ventral) and another that guides our actions (dorsal) → some evidence comes from a patient who has associative agnosia

• according to this theory, the secondary visual pathway projects to the dorsal stream → which is important for vision for action.

• this theory holds that the ventral stream is more important for generating conscious visual sensations (vision for perception)

what are some theories for the binding problem

• the binding problem is solved by synchronous neural activity. Another suggestion is that feedback may be involved. Another suggestion is that the binding problem could be solved via attention.

• the attention suggestion is called/supported by the feature integration theory and is thought to be provided by instances of illusory conjunctions

what are lateralised functions 

• the idea that some brain functions rely more on one side of. the brain than the other

• however there is no overall dominant hemisphere

what are the lateralised functions of the left and right hemisphere

• left hemisphere: language/speech comprehension and production, reading

• right hemisphere: tone of voice, face perception, perceptual grouping

what are the contralateral (combined) functions across the hemispheres

• movement, sensation, and vision

difference in language lateralisation for right and left handed people

• right handed people → 95% have language in left hemisphere

• left handed people → 70% have language in left hemisphere

contralateral vs ipsilateral

• contralateral → opposite side

• ipsilateral → same side

explain the primary motor and sensory cortex in relation to the hemispheres

• connects to contralateral side of the body

1. right hemisphere to left side of body

2. left hemisphere to right side of body

explain vision in relation to the hemispheres

• each side of visual space is mapped to contralateral visual cortex

1. left side of vision to right hemisphere

2. right side of vision to left hemisphere

• note; not left eye/right eye (only left/right side of visual space)

what is the corpus callosum

• connect the left and right hemisphere → axons of neurons cross to the opposite hemisphere → allows the transfer of information between the two hemispheres

explain an example of transfer of inter-hemisphere communication

• vision goes to contralateral hemisphere

• in a lab you can present stimuli very briefly to the left or right of the screen

• stimuli go selectively to right or left hemisphere

• language is in left hemisphere → can report on what is on right side of screen

• however, stimuli on the left side of screen goes to right hemisphere → therefore information must cross to left hemisphere for language to report what the object was.

• inter-hemispheric communication is across the corpus callosum 

what is split brain

• used as a last resort surgical treatment for very severe epilepsy → the corpus callosum is severed to stop seizure activity from spreading to the other hemisphere

what did sperry and gazzaniga study

• looked at split brain patients which led to much knowledge about lateralisation of brain function

• their experiments would involve:

1. images flashed to left or right of screen → seen by only left or right hemisphere

2. people could reach under screen to touch and feel the objects → find them by feel

what did they find 

• showed that right hemisphere can read and understand words but has no speech

• left hemisphere can tell what it has seen and right hemisphere can only show it (via the left hand). However, the patient cannot say what their left hand is doing

what is the hippocampus and function

• the hippocampus is apart of the limbic system and is responsible for
  1. memory → forming new episodic memories
  2. spatial navigation → mental map of familiar environment

what was the case study of HM

• HM had his hippocampus removed to treat epilepsy. However, it caused severe memory loss;

1. he could not form new memories or recall anything after surgery

2. could remember and recall things from before surgery

3. could mentally rehearse to remember things for a fre seconds

4. could learn new skills

what did the case study of HM tell us about memory

• short term memoy → lasts several seconds

• long term memory → there are four components

• from HM we could determine that the hippocampus was related to the long term declarative memory. Specifically, the hippocampus is also actively involved in the encoding of declarative long term memory

what are the four components of long term memory

1. declarative → conscious recollection

2. episodic → memory of past events, things you have seen and done

3. semantic → facts and basic knowledge you can recall and declare

4. procedural → not for conscious recall (ie. skills you have learnt)

what are the two processes long term memory is involved in

1. encoding → laying down new memories for long term storage

2. retrieval → retrieving memories for conscious recall

what is the most common place for epilepsy

• the medial temporal lobe → this is because epilepsy piggybacks on the mechanisms that allow memory to occur (neuroplasticity)

what does long term epilepsy in the medial temporal lobe cause

• will see a loss of neurons. And the hippocampus will progressively shrivel up → this will cause memory deficits

• there will be increased risk of neuronal loss through repeated epileptic seizures

how can we manage epileptic seizures

• through medication or surgical options (ie. removing the hippocampus or sight of seizure

• if we remove one hippocampus we need to have cognitive reserve (ie the other one needs to be functional 

how can we determine if there is a risk of cognitive dysfunction from removing the hippocampus

• through the WADA test → this is a technique that involves anesthetizing one hemisphere selectively and during this period we can retest cognitive functioning. 

what is perception and behaviour a combination of

1. bottom up processes → driven by external stimuli or unconscious states

2. top down processes → cognitive control or volitional choice; modulate by prior knowledge and experience

what is the parietal lobe and function

• posterior to the central sulcus; manages attention:

1. directing attention to explore visual world

2. spatial neglect (parietal lobe damage

• also manages spatial awareness:

1. linking vision to action

2. represents spatial location of objects around us for guiding actions

3. mathematics ability and map reading

why was William James’ definition of attention important

• had the important aspect of selectivity; that attention is selecting one out of several simultaneously possible objects or train of thought

what are the components of attention

1. selectivity → select and prioritise stimuli based on locations or features (ie. moving spotlight and relevant features)

2. capacity limited → resources for attention are limited, we cannot attend to all incoming sensory information so we use attention to filter and prioritise sensory information

what is conscious controlled attention

• top-down process: selecting and prioritising according to task or goal, voluntarily shifting visual attention to search, choosing features for selection or focus of attention

what is automatic attention

• bottom-up process; attention captured involuntarily by high salient stimuli, things that stand out or pop out (ie. sudden movement)

• advertisers use this very well

what did corbetta and schulman find

• network of prefrontal and parietal cortex mediate attention

• different areas for goal directed (dorsal) and stimulus driven (ventral) attention

• based on brain imaging (MRI) studies and patients with brain lesions (spatial neglect)

what is spatial neglect

• lesions to the parietal cortex (most commonly caused by stroke)

• deficit in directing attention to one side of space 

• unable to perceive stimuli on side contralateral to brain lesion

• not due to any sensory deficit (ie. normal vision)

what are the clinical tests for spatial neglect

• using a paper and pencil performed in interview or bedside (ie. complex figure drawing task) → people with spatial neglect won’t draw one half of the picture

• this can give us quantitative data

• another symptom is simultagnosia → cannot perceive multiple objects simultaneously (will ignore objects on the neglected side)

what is the frontal lobe and functions

• the frontal lobe is anterior to the central sulcus

• manages cognitive control of behaviour and also manages executive functions:

1. reasoning, planning, problem solving

2. inhibitory control

3. working memory

what is control of behaviour reliant on

1. selection of appropriate actions

2. inhibition or suppression of inappropriate actions or usual response (task-switching)

what disorders are associated with inhibitory control

1. ADHD

2. OCD

3. reward addictions

what did Egas Moniz introduce

• prefrontal leucotomy for the relief of psychiatric disorders

• this was based on the observations of temperament changes in chimpanzees following frontal lobe lesions

• used for severe psychosis but stopped after the introduction of antipsychotic medication

what did Walter Freeman introduce

• developed frontal lobotomies via psychosurgery by the bedside

what is fronto-temporal dementia

• degeneration in the frontal and temporal lobes → helps show us the function of the frontal lobes 

what are some symptoms of fronto-temporal dementia

1. disinhibition in behaviour

2. apathy

3. deficits in executive functions

4. loss of empathy

what are the two types of fronto-temporal dementia

1. behavioural variant

2. language variant (3 variants)

what is the characteristics of the behavioural variant

• the main difficulty is social comportment (behaving appropriately)

• involves predominantly frontal atrophy

what are the three different language variants

1. non-fluent primary progressive aphasia → speech is effortful and hard to get out, lacking grammar

2. logopenic progressive aphasia → pauses in speech or repetition 

3. semantice dementia → nonsense speech, understanding is disintegrating