To See Or Not To See

Question 1

To what extent is movement contra-lateralised

Answer 1

To a large extent, movement, along with most stuff is contra-lateralised but for motor cortex (SM1, SMA, PMC, PPC ), contralateral control of movement is NOT ABSOLUTE:

Particularly for proximal muscles (e.g. shoulder, trunk) control is largely bilateral (C, D) Only for distal movements (e.g. fingers), motor control is largely contralateral, although even there, there are some ipsilateral contributions (A, B), particularly for the non dominant hand (left hand, B)

Question 2

What is probably the most lateralised of human cognitive functions?

Answer 2

Language production and comprehension (maybe even more so for comprehension)

Question 3

How was the area required for speech production determined and what name was given to it?

Answer 3

French neurologist Paul Broca studied the brains of mr Leborgne (‘Tan’) and Le long (and others), suffering from severe aphasia. He concluded that speech production depends on a region in the ‘third convolution of the frontal lobe’. This is now called Broca’s area.

Question 4

Why may the story regarding Broca’s area be a bit more complex than posed here?

Answer 4

As damage to Broca’s area results in temporary speech deficits, and MRI of Leborgne’s and Lelong’s brains revealed much deeper damage (Either way, speech production seems highly lateralized in most people.)

Question 5

Which side is speech lateralised in people

Answer 5

For most people left (inferior frontal gyrus) but not all people, some are right hemisphere or a bit of both

Question 6

Why can the two hemispheres usually work together?

Answer 6

The two hemispheres normally work together because the Corpus Callosum connects the cortex of the two hemispheres Together with Anterior Commissure (not always cut in surgery)

Question 7

Name the parts of the corpus callous from most rostral to caudal and the structure beside each end

Answer 7

Anterior commissure (rostrum, genu, body, splenium) posterior commissure.

See copy/ docs for diagram

Question 8

What role does the posterior commissure play?

Answer 8

Posterior Commisureconnects subcortical nuclei

Question 9

What is meant by homotopic and heterotopic topic areas?

Answer 9

Homotopic areas connect to the same structure on the contralateral side, heterotopic areas connect to different contralateral brain areas

Question 10

Before split brain procedures, how was the activity of one hemisphered studied independent of the other?

Answer 10

The Wada test: each hemisphere is temporarily anesthetised using amobarbital (or sodium amytal, etc).

Question 11

What was often the results of the Wada test?

Answer 11

In most people, anesthesia of the left hemisphere results in aphasia, the inability to speak or comprehend language. But some people have right hemisphere dominance for language, others bilateral language capabilities

Also, the left hemisphere cannot ‘remember’ what the right hemisphere did after it regains consciousness (b)The right hemisphere, meanwhile, does remember what it did, but cannot express this verbally, only manually (by pointing) (c)

Question 12

How did split brain patients first come about? Were these effective?

Answer 12

The first partial callosotomies were performed in 10 patients suffering from severe epilepsy (1940). Results were mixed, with some 60% of patients finding relief.

Question 13

Give a possible reason for the mixed results found in these split brain patients

Answer 13

Mixed results probably due to partial cut of corpus callosum (mid part mainly)

Question 14

What personality changes were observed in these split brain patients

Answer 14

Psychological tests revealed no pronounced changes in personality, intellect, sensory or motor performance

Question 15

Name the four main protagonists in splitting the brain and what they contributed

Answer 15

William P. Van Wagenen- did the previously mentioned cuts for severe epilepsy

Joseph Bogen- Performed the first series of full split brain surgery in human patients to relieve epilepsy (1962)

Roger Sperry- Received Nobel prize for fundamental work on split brain patients and animals (1981)

Micheal Gazzaniga- Student of Sperry’s, continued the work and built theoretical framework

Question 16

What happens when the posterior part of the callosum is sectioned?

Answer 16

When the posterior part of the callosum is sectioned, higher order, abstract information about the stimulus can be reported, not the stimulus itself (middle panel)

Question 17

Describe a task which demonstrates the remaining capabilities for ‘not seen’ stimuli in split brain patients and what these capabilities are

Answer 17

Two words are shown in the left and right hemispheres. The patient is asked to say which word he sees. He will say the word in the right hemisphere, however with his left hand he can

• Draw the object named
• select/ point to it
• match objects to words
• Other simple semantics
• Recognise family/ famous people
• Give emotional responses

Despite not ‘seeing anything

Question 18

What is meant by ‘other simple semantics’ in terms of the capabilities of split brain patients

Answer 18

For example a horse is shown, asked “what is it? what goes on it?” “Idk” But can draw a saddle.

Question 19

What is the right hemisphere better at recognising, if not words? When does this not hold true?

Answer 19

Recognising/ matching faces but only when no verbal descriptions of faces can be made (blonde vs brunette)

look at doc for example

Question 20

Correlating with this greater ability in matching faces, what brain area is more prominent in the right hemisphere?

Answer 20

Fusiform face area (FFA)

Question 21

What wider ability of the right hemisphere may the greater ability in processing faces be related to?

Answer 21

This may be related to the right hemisphere more prominently processing ‘the big picture’, doing perceptual organisation.
(Apperceptive and Integrative Agnosia are problems with perceptual organisation, binding features into a coherent percept, and are mainly caused by right hemisphere lesions)

Question 22

When showing pictures to the left and right hemisphere, they may differ in their opinions on whether they have seen the picture before. Explain this.

Answer 22

Left hemisphere falsely recognises pictures because they ‘fit the story.’ Right hemisphere rightfully rejects these as not seen before

Question 23

What do these picture stories demonstrate about the hemispheres?

Answer 23

Left hemisphere seeks patterns and sequences in events

Question 24

Describe the process and results of another study which demonstrates how the left hemisphere seeks patterns and events

Answer 24

Split brain patients had to predict red or green as best as possible. The light was free 30% of the time, red 70% of the time. Matching strategy would be to press the green button 30% of the time and the red button 70% of the time. Maximising strategy (more effective) would be to press the red button 100% of the time.

The left hemisphere uses the matching strategy while the right hand side uses the maximising strategy.

Question 25

How do rats act in these minimise/ maximise tasks?

Answer 25

Maximise

Question 26

Would you say that the right hemisphere is unconscious in split brain patients? What question arises with this problem

Answer 26

Is the right hemisphere UNCONSCIOUS, or just not communicating (because it has no language)? could this be compared to locked-in syndrome? It uses strategies, can draw, select, recognising family, emotional responses.

Where lies the boundary for conscious experience?

Arguing either for or against the right hemisphere having conscious sensations implies laying a boundary between cognitive functions that do or do not count as ‘evidence’ for having conscious experience.

Question 27

Describe some remarkable findings during WW1 which lead to the discovery of a brain condition which concerns the topic of conscious experience.

Answer 27

Soldiers often went on fighting after being shot in the head only to realise later they were shot and partially blind. On testing, Riddoch found some cases of blind patients that could still ‘see’ motion. This was dismissed by Holmes as nonsense: how can you see motion without seeing what moves.

Question 28

What lesions were these soldiers likely suffering from and name is given to these visual impairments (2)? (discounting them seeing movements for a minute)

Answer 28

Lesions of striate cortex (V1) result in cortical blindness. Patients insist they ‘see nothing’, have ‘no visual sensation whatsoever’, are ‘not aware of anything happening on that side.’

This is confirmed by perimetry testing of the visual field, e.g only having half their field of vision; patients with unilateral lesions to V1 >hemianopia.

Question 29

How did researchers come to the conclusion that these patients could see movement? What name was given to this condition?

Answer 29

If a stimulus is moving fast enough then they do perceive movement and can tell the researcher the direction of motion of the stimulus. The blindsight finding is that people will not ‘see’ this motion but will be able to ‘guess’ the movement, but others could see the movements at high speed (like waving a hand in front of the light.) It is this discrepancy that we call blindsight.

Question 30

What other discoveries were made about these patients? (4)

Answer 30

Despite claiming they did not know where the stimulus was, when pressed they would correctly point their finger to stimuli in the blind hemifield.

They could discriminate between two shapes the stimulus could have been highly about chance despite claiming they did not know. (X vs O)

Spatial summation across the midline: faster reaction to two stimuli in blind and intact hemifield than to one stimulus in intact hemifield

‘Attentional blink’: slower RT when stimulus in intact hemifield is preceded by stimulus in blind hemifield

Question 31

What question regarding blindsight is still debated today?

Answer 31

Whether ‘blindsight’ is merely degraded normal vision or whether it represents qualitatively distinctive visual capacity

Question 32

How could blindsight patients have qualitatively distinctive visual capacity and how is this argued?

Answer 32

Blindsight capabilities are typically somewhat -or quite far -below normal visual capabilities. They tend to have fairly low visual acuity, and lower precision. Some have argued that they are mediated by Y-type retinal of magnocellular LGN pathways, conveying only low spatial frequency information. Indeed, color tasks present the most challenges to blindsight patients, while they are best at localization, motion, and other properties carried by the dorsal pathways.

Question 33

What is blindsight most likely mediated by? What have others suggested?

Answer 33

Blindsight is most likely mediated via the projections of the optic tract to the superior colliculus, which projects to the dorsal stream areas, like MT and parietal cortex.

Although others have suggested connections from LGN to MT or extra-striate cortex, or callosal connections from the other hemisphere

Question 34

What evidence is there for this theory of SC projecting to the dorsal stream areas, like MT and parietal cortex.

Answer 34

Responses of MT neurons are weaker after a V1 lesion but remain present. Their direction selectivity and direction tuning remains unaltered.

However, a combined V1 and Superior Colliculus removal totally abolishes responses (at the visual field location where both lesions overlap).

Question 35

Describe a study and its results which demonstrated the role of a further brain area in the neural mechanisms of blindsight

Answer 35

Despite unilateral lesions (a) to V1, monkeys could still make saccadic eye movements to targets in the contralesional hemifield (i.e. had ‘blindsight’, (a)).

However, an injection of muscimol (which inhibits neural activity) in the Pulvinar abolished this capability (b,c,d,e)

see docs

Question 36

Name and briefly describe two typical tests for blindsight in humans

Answer 36

The typical dissociation in human blindsight patients is above chance performance in a forced choice (FC) task while patients deny seeing or a Yes/No (YN) task (like perimetry, other detection task, or just asking)

Question 37

How were they able to know whether these monkeys actually had blindsight using these FC and YN tasks?

Answer 37

They were trained to perform either a FC or a YN task. In FC their saccadic eye movements could be tracked for a reward. In the YN task ‘no’ was indicated by maintaining fixation on centre during target absent trials (ST-)

In the intact hemifield, at high target contrast both the FC and YN task yield near perfect performance. With very low contrast, performance drops about equally for FC and YN tasks.

In the affected hemifield, however, there is a strong performance drop for the YN task, while the FC task remains at high levels > Blindsight in monkeys

Question 38

What method was used to determine whether these monkeys truly had blindsight? Name and describe it

Answer 38

Standard Signal Detection Theory: stimulus A versus B (or absent vs present) generate different internal representations, that are noisy, and distributed as Gaussians. The observer sets an internal criterion. If the signal exceeds the criterion, the observers says A, if it is below, he says B (or Y/N).

HIT = saying A when there is A,
MISS= saying B when there is A.
Correct Rejection (CR) = saying B when B, 
False Alarm (FA) = saying A when B. 

By manipulating criterion, Hits and FA’s will change. Plotting FA’s vs Hits gives a Receiver Operator Curve. The d’ is the discriminability of the two stimuli

see docs for relevant graphs (or slide 39)

Signal detection theory analysis revealed that in the affected hemifield there is a real drop in Da (sensitivity), independent of decision criterion. This indicates that blindsight is NOT like near threshold vision, but true ‘unconscious’ vision

Question 39

Do people and animals suffering from cortical blindness usually use their blindsight? Explain

Answer 39

Humans with cortical blindness do not usetheir blindsight abilities. They don’t trusttheir unconscious visual signals.

Some monkeys, on the other hand, may behave quite normal, as if they don’t care about being cortically blind.

Question 40

What could this difference in how monkeys and humans behave with cortical blindness suggest?

Answer 40

Maybe the monkey is not conscious anyhow, so he doesn’t care about the difference between conscious and unconscious vision?

Question 41

What else makes a difference in how monkeys (and people) behave with blindsight? Explain the difference that it makes

Answer 41

Unilateral versus Bilateral lesion also makes a large difference.

Monkeys (and humans) with bilateral V1 lesions behave almost normally: superblindsight

Question 42

What could the information from these blindsight patients add to the dorsal and ventral stream theory?

Answer 42

Perhaps the dorsal stream is for unconscious visually guided action while ventral is the site where conscious sensations are produced

Question 43

However what, mentioned earlier, can refute this theory of the dorsal stream being ‘blind’?

Answer 43

The idea that dorsal stream is ‘blind’ and does not contribute to conscious visual sensations is however immediately refuted by the finding that blindsight patients do perceive motion when the motion is fast enough.

Patients describe their percept as ‘objectless movement’ a raw sense of motion, as if you wave your hand in front of your closed eyes while looking at the bright sky

Question 44

What other evidence is there against the notion that the dorsal stream is ‘unconscious’?

Answer 44

MT neurons with a specific direction of motion preference (established after recording from them) are electrically stimulated while the monkey is viewing random dot motion in two directions (either the preferred direction of motion of the cells that are stimulated, or the opposite direction), and with different coherence of motion (% motion strength).

Monkey should indicate what direction of motion he perceives by making saccade to one of two positions. Without stimulation, monkey reports direction that is presented more often, depending on motion strength (blue curve). When electrically stimulated, the monkey more often reports seeing motion in the preferred direction of the cells (red curve), even when motion is actually in the other direction.

Question 45

How is unconscious visual processing studied in normal subjects?

Answer 45

Masking e.g fixations point, forward mask for 500ms, face shown with particular emotion 20ms, backwards mask 500ms. Then asked preference such as, ‘do you think this Chinese character is a happy work’ (preference task’ or a visibility task simply asking happiness.

while people do not consciously report the stimulus it is shown that the facial expressions affect their preference etc. Note that these are not shown super briefly so they would not be perceived alone- they need the masks to become ‘invisible’

Question 46

Describe a more effective way of masking that is often used

Answer 46

Metacontrast masking- Contours of target and mask overlap. Maximal masking with some positive SOA; e.g grey dot first shown then darker surrounding circle, arrow then larger arrow with hollow middle befitting it and asked which direction was the arrow pointing

Question 47

What time is most effective for metacontrast masking?

Answer 47

around 50-100ms

Question 48

What are usually the results found with metacontrasting? (arrow task)

Answer 48

Metacontrast masking conceals orientation of prime (subjects remain at chance level in detecting prime orientation, panel d). Yet the invisible primes influence reaction time (b) to a subsequent target (that also functions as the metacontrast mask, a)

Question 49

Aside from masking, how else can you make a stimulus ‘invisible’? Name and explain

Answer 49

In Continuous Flash Suppression (CFS) the stimulus in one eye is strongly masked by a high contrast, colorful, rapidly changing (moving) image in the other eye. This renders the stimulus invisible.

Question 50

What is CFS used to study/ measure?

Answer 50

The extent of ‘subconscious’ processing of the masked stimulus is studied by showing that it can induce adaptation, prime subsequent categorisation or break from suppression (become visible, earlier than some other stimulus (e.g. upright versus inverted faces).

Question 51

What results were found from these CFS studies regarding breaking CFS? (2)

Answer 51

Breaking CFS (bCFS) reveals that very complex analyses are performed before a stimulus enters awareness. For example, upright faces break through faster than inverted faces (> face processing is done pre-consciously). But also, faces of own race or own age break through faster (> familiarity of faces is processed pre-consciously). In this way, it was shown that face attractiveness, emotional expression, etc is processed pre consciously

Also erotic images unconsciously draw attention depending on sexual preference.

Question 52

What critique was there on the breaking CFS paradigm methodology?

Answer 52

Pushed it almost to the extreme, suggested that almost anything can be processed unconsciously

Question 53

What problem is this critique of breaking CFS an example of in researching unconsciousness?

Answer 53

Objective versus subjective invisibility (e.g ranking on an awareness scale).

Question 54

When is it objective invisibility?

Answer 54

The the performance (e.g Y/N task) is chance level. Subjective invisibility is generally more lenient. There is often still above chance discrimination on subjectively invisible trials.

Question 55

What problems present themselves with objective invisibility?

Answer 55

Objective invisibility suffers from the problem ‘what to ask’. Discrimination (upright or inverted?) vs Localization (;eft vs right) vs Detection (seen vs unseen) all give different results.

Question 56

When studying the differences between subjective and objective visibility, what is observed neurologically?

Answer 56

They have different neural correlates. The brain still differentiates between face / house for subjectively invisible stimuli. For objectively invisible stimuli (discrimination) there is no differential face / house signal.

Therefore again, when do we call something unconscious?

Question 57

What idea did people have rather than contrasting seen and not seen?

Answer 57

insteadof contrasting‘seen’ vs ‘not seen’ we contrast ‘seeing A’ vs ‘seeing B ’

Bistable stimuli: Stimulus remains constant, yet conscious percept switches spontaneously

Question 58

How can this bistable stimuli be perceived?

Answer 58

illusions (old, young woman etc) and binocular rivalry.

Question 59

Describe binocular rivaly

Answer 59

Presenting two different stimuli to the two eyes (stationary for minutes) results in spontaneous switches of perceiving the one (say left eye) stimulus, then the other (right eye), then the first again, etc. Dominance lasts several seconds, but may vary in length from switch to switch.

Question 60

How does the dominance length differ between humans and monkeys?

Answer 60

Dominance length has a characteristic frequency distribution, that is the same in man and monkey

Question 61

What can cause one image to dominate more than another? is this the same between men and monkeys? (2)

Answer 61

A stimulus that is ‘sharper’ (i.e. contains more high spatial frequencies) will dominate longer than a stimulus that is unsharp.

Also, a stimulus that is higher contrast will dominate longer than a low contrast stimulus.

Again, this is the same (or similar) in man and monkey

Question 62

What neural results are reported when faces and non faces are shown in binocular rivalry

Answer 62

Face selective cells in IT respond stronger (or only) when the face is dominating (seen) in binocular rivalry

Question 63

What can therefore be concluded about consciousness and these higher level neurons?

Answer 63

Unfortunately not as simple as just saying that the higher level cells are neural correlates of consciousness.

Binocular rivalry has also been studied extensively un humans using fMRI. The (spontaneous) transition from perceiving a house to seeing a face is accompanied by activation of the PPA going down, the FFA going up. The opposite transition (face > house) is accompanied by an increase of PPA, lowering of FFA activation.

However this has also been observed in lower visual areas too with simpler stimuli too. Which visual areas change activity with BR switches depends on stimulus characteristics. For oriented gratings, the perceptual switches can be decoded from early visual areas like V1, V2, V3, rather than from higher visual areas.

Question 64

How do we know whether this decoding is accurate?

Answer 64

The activity once decoded can be used to predict when the person perceived which stimulus. This is then contrasted against the persons report on their perception. This is usually quite accurate.

Question 65

What is meant by motion induced blindness?

Answer 65

Things disappearing due to the motion (eg yellow dots and navy rotating grating)

Question 66

How is motion induced blindness similar and dissimilar to ocular dominance in perception

Answer 66

Motion Induced Blindness has many similarities with binocular rivalry. The (yellow) targets disappear and re-appear spontaneously, with varying and random intervals. A difference is the asymmetry of dominance. The yellow targets are visible for longer periods than they are invisible.

Question 67

What do you get when looking at fMRI during motion blindness

Answer 67

Responses to the yellow target are reduced when it is not seen and responses to the moving background are increased.

The opposite happens when the yellow target re-appears: increase in activation of the response to the target, decrease of response to surround

Question 68

Can what’s being perceived in a bistable stimulus regarding motion direction be decoded from fMRI or not?

Answer 68

yes: the rotating random dot sphere. This spontaneously alternates between seeing clockwise (CW) or counter clockwise (CCW) movement. What is seen by the subject can be decoded from motion sensitive and parietal areas involved in 3D perception