Attention and Consciousness

Question 1

What is resting state activity?

Answer 1

• Brain activity while at rest in certain regions
• Moving from resting state to performing a cognitive / behavioural task is associated with decreased activity in regions that are activated during rest

Question 2

What four regions are a part of the default mode network? What kind of activity do these brain regions show while at rest?

Answer 2

1. Medial PFC
2. Posterior cingulate cortex
3. Hippocampus
4. Lateral temporal cortex

• Brain defaults to activity in this group of interconnected areas when it is not engaged in an overt task
• Very high correlation in brain activity between these regions

Question 3

Name and describe the two hypotheses regarding the function of the DMN.

Answer 3

1. Sentinel hypothesis
   - Humans broadly monitor their environment, even at rest
   - Posterior cingulate cortex is thought to be responsible for monitoring visual fields for stimuli and is damaged in simultagnosia (trouble identifying more than one object at a time)
   - There is an evolutionary advantage to always being on the lookout
   - When active focus, is shifted to task at hand
2. Internal mentation hypothesis
   - Supports thinking and remembering that occurs during daydreaming
   - Activity increases when patients are asked to quietly sit and think about past or future events
   - Autobiographical memory tasks

Question 4

What is selective attention?

Answer 4

• The ability to direct attention to select objects / stimuli
• The selective processing of sensory input
• Allocation of neural resources to the analysis of a particular information at the expense of resources that might have been allocated to other concurrent information
• Measured with dichotic listening task

Question 5

What is the difference between bottom-up and top-down attention?

Answer 5

• Bottom-up: Stimulus attracts our attention without any cognitive input
• Top-down: Attention is deliberately directed by the brain to some object or place to serve a behavioural goal

Question 6

What is the late selection model of attention?

Answer 6

• Proposes that information filtering occurs relatively late in sensory processing pathways
• Only after high level processing does attentional mechanisms determine what input enters consciousness / influences behaviour
• Appears to be a threshold of relevance for further processing and early entry into consciousness

Question 7

What is the difference between overt and covert attention?

Answer 7

Overt

• Moving our eyes to focus an image of interest on the fovea of each eye
• Orienting head and eyes to stimulus to improve perception

Covert

• Somehow directing attention to a stimulus without moving head or eyes
• Shifting attention to objects imaged on parts of retina outside of the fovea (periphery)
• Less sensitive to stimuli in opposite half of visual field

Question 8

What are the two ways that focusing attention enhances visual processing of a location?

Answer 8

1. Enhances visual sensitivity
2. Speeds up reaction time

• task: participant’s eyes are fixated on the centre of the screen. cue is flashed either to the right or the left. actual object is either flashed on the same side, the opposite side, or neither.
• When the cue is valid, target detection increases while reaction time decreases relative to neutral and invalid cue.

Question 9

What is the spotlight of attention?

Answer 9

• When we know where something is likely going to be, we shift our attention towards it and process the sensory information with greater sensitivity and speed
• Spotlight moves to illuminate objects of particular interest or significance
• Shifting of attention is associated with changes in brain activity

Question 10

Explain the experiment that demonstrated the spotlight of attention.

Answer 10

• Patients asked to fixate on centre of grid
• Task was to press a different button depending on the colour and pattern of a given sector
• Cued sector changed every 10 seconds
• Brain activity shifted further away from the occipital pole as the attended sector moved out from the fovea
• When cued sector was close to where the eyes were fixated, there was lots of activity in the occipital pole
• Visual attention can be moved independently of eye position
• Neural effect of the spotlight of attention moving to different locations

Question 11

Explain the study that asked participants to use top-down attention to determine if images were the same or different.

Answer 11

• One condition was selective attention: Paid attention to only one feature (e.g., colour)
• Other condition was divided attention: Paid attention to all features
• Different areas of cortex had higher activity when different attributes were being discriminated
• Ventromedial occipital cortex: colour and shape
• Parietal cortex: Direction and speed of motion away from fovea

Question 12

What were the 3 main conclusions of the previous experiment?

Answer 12

1. Many brain regions are involved in attention
2. Different brain regions are associated with different kinds of attention
3. There is strong overlap between the circuits that control attention and those that govern movements of the head and eyes. Attention circuits may have been built upon systems that originally evolved to orient organisms to objects and events in their environment.

Question 13

What is hemispatial neglect? What brain region is damaged in this condition?

Answer 13

• Unilateral deficit of attention: Patients ignore objects, people, and own bodies on one side of centre of gaze
• Attentional problem rather than sensory
• Patients have an inability to switch their attention and typically objects in the right visual field are abnormally effective in catching attention
• Difficulty disengaging attention
• Most commonly associated with damage to the posterior parietal cortex of the RH – can also occur after damage to the PFC, cingulate cortex, and other areas

Question 14

What is the role of the Pulvinar nucleus of the thalamus in attention?

Answer 14

• Pulvinar neurons respond more robustly when a stimulus is present in the receptive field vs. when attention is directed elsewhere
• Has reciprocal connections with visual cortical areas of the occipital, parietal, and temporal lobes
• Modulates widespread cortical activity
• There is highly synchronized activity between pulvinar, V4, and IT cortex. Pulvinar provides input to V4 and IT and regulates information flow in areas of visual cortex.

Question 15

What happens when there are pulvinar lesions?

Answer 15

• Abnormally slow response time to visual stimulus on contralateral side
• More pronounced when you present competing stimuli on ipsilateral side
• Reduced ability to focus attention on objects in contralateral visual field
• Injecting GABA antagonist into pulvinar nucleus facilitates shifting attention to contralateral side.

Question 16

What is the role of the frontal eye fields in attention?

Answer 16

• Direct connections to V2-4 and parietal cortex
• Have motor fields that control movement of the eyes to a specific region of the visual field
• Stimulation of neurons in FEF causes eyes to rapidly make a saccade to motor field of stimulated neuron
• Lesions to FEF disrupts ability to initiate eye movements to targets in contralateral visual field
• Activation of neurons in FEF increase attention within the corresponding motor field but not outside of that motor field
• Provides an attention boost: FEF neurons can draw attention towards a particular motor field but also draw attention away from others
• FEF is involved in task switching and ignoring irrelevant information

Question 17

How does the FEF direct attention to enhance location specific visual performance?

Answer 17

• FEF neurons indicate the location of future saccadic eye movements
• Information is then relayed to cortical areas it is connected to and enhances activity in these areas
• Contributes to physiological and behavioural effects of visual attention

Question 18

What is the lateral intraparietal cortex’s role in attention?

Answer 18

• Located in posterior parietal cortex
• Constructs priority maps based on both bottom-up and top-down inputs
• Priority map: Map showing locations where attention should be directed based on stimulus salience as well as cognitive input (e.g., flashing light in receptive field and your friend’s voice in a crowded bar)
• Plays a role in directing eye movements to direct attention. Lesions are associated with neglect syndrome.
• Carry information appropriate for a priority map of visual attention.

Question 19

Explain how the frontoparietal attention network mediates bottom-up attention.

Answer 19

• Input from visual areas reaches area LIP
• Area LIP constructs salience map based on conspicuous objects in field of view
• FEF also contains salience map that is signalled after LIP
• Feedback to visual areas and connections with eye movement structures, allowing visual processing of salient objects to be enhanced
• Eyes move to foveate the object

Question 20

Explain how the frontoparietal attention network mediates top-down attention.

Answer 20

• Frontal lobe is critical for directing behavioural goals and controlling attention
• First, PFC and FEF are activated. Then, there is progressive activation of LIP, V4 & MT, V2, then V1
• Behavioural goals are established in frontal and parietal areas, information is processed to create a priority map in LIP and FEF and modulation of visual cortical areas enhances perception of selected objects

Question 21

Explain the materialist and dualist perspectives of consciousness.

Answer 21

Materialist
- Consciousness arises from physical processes and therefore can be understood as being based on structure and function of the nervous system

Dualism
- The mind and body are different things and one cannot be fully explained by the other. Therefore, consciousness cannot be fully explained by physical processes.

Question 22

What is the neural correlates of consciousness?

Answer 22

• The minimal number of neuronal events sufficient for a specific conscious percept
• What must happen in which neurons for you to experience a conscious event
• The difference between neural processes that occurs when we are aware of something vs. when we are not
• Studied using bi-stable images: Assess nature and location of neural activity while a particular sensory percept moves in and out of awareness

Question 23

How is binocular rivalry used to study attention?

Answer 23

• Eyes have two different images
• Perceptual awareness alternates between the two images
• By using electrophysiology / brain imaging, can see changes in brain activity when there is a switch of conscious content

Question 24

What visual area is associated with stimulus awareness in monkeys?

Answer 24

• Correlation of neural activity with stimulus awareness increases as the recording site moves away from V1 along the ventral pathway
• Area IT has been implicated in altering perception in binocular rivalry
• Low level visual neurons are about as active when subjects are aware of a stimulus vs. when they are not

Question 25

Explain the binocular rivalry experiment and what it revealed about area IT’s role in consciousness.

Answer 25

• Starburst presented to left eye and animal face to right eye
• Monkey alternately pulled left or right lever suggesting that it alternately perceived the starburst or animal face
• Response of IT neurons fluctuated between low and high activity roughly in sync with the animal pulling the left or right lever, even though the stimulus was fixed
• Correspondence between changes in activity of IT neurons and perception
• Binocular rivalry produces an alternation in the conscious awareness of images, and activity of IT may correlate with this awareness

Question 26

What areas in humans are associated with perceptual changes in binocular rivalry?

Answer 26

• Associated with activity in frontal and parietal cortical regions
• Activity in these regions time-locked to subjects’ reports of perceptual changes
• “Pop out” of a visual stimulus is strongly associated with activity changes in frontal and parietal lobes
• TMS inactivation of these regions disturbs perception of visual stimulus

Question 27

Explain the findings that suggest that consciousness might be context /object specific.

Answer 27

• FFA responds preferentially to faces while PPA responds to pictures of houses and other physical places
• During rivalrous state, house-to-face transition associated with decrease in PPA activity and increase in FFA activity (reverse as well)
• Activity of regions may represent neural correlates of consciousness to faces and houses