Attention

Question 1

What are the two key aspects of attention, and what do they refer to?

Answer 1

Capacity limitation – central resources for processing stimulus inputs are limited; resources are allocated automatically to all stimuli until capacity is exhausted; Selectivity – stimulus inputs can be prioritised based upon their locations or elementary features (e.g. colour/orientation)

Question 2

In what way are capacity limitation and selectivity two sides of the same coin?

Answer 2

Because we have a limited capacity, we have to be selective

Question 3

Why is it more difficult to find the target in conjunction or spatial orientation search tasks than feature (pop-out) searches, especially when more distractors are present?

Answer 3

There’s no unique feature (colour/orientation) of the target; have to combine both components so it takes longer

Question 4

Which neural areas are particularly important for attention processing?

Answer 4

Parietal cortex and lateral PFC

Question 5

What does the inferotemporal cortex respond to?

Answer 5

Complex features, such as faces

Question 6

Describe two important features of the primate visual system

Answer 6

They’re modular (different regions are responsible for different types of processing); and hierarchical (higher levels, such as parietal and inferotemporal respond to more complex features)

Question 7

What are two distinguishing features of neuronal receptive fields?

Answer 7

Variable size (smaller receptive fields in V1, which get larger further up the hierarchy); and each have different preferred stimuli

Question 8

Parietal neurons in which region of monkey brains have been implicated in modulating attention during attentional tasks?

Answer 8

Lateral intraparietal (LIP)

Question 9

Compare the LIP activations in monkeys when doing a task where an irrelevant stimulus is flashed to the side of fixation, and when there’s fixation with attention to peripheral stimulus to detect brief dimming (with a reward)

Answer 9

Much more neurons firing in the latter case, as they’re motivated to receive a reward, and have shifted attention here; attention is modulated according to relevance

Question 10

Which area of the visual cortex contains neurons with large receptive fields that are tuned to colour and shape?

Answer 10

V4

Question 11

Mangun et al. had Ps fixate in the centre of a screen and presented a white bar to the left or right of the visual field. They were told to either attend to it or ignore it and attend to the other side. When was there a boost in ERP response (in component P1)?

Answer 11

When the stimulus appears on the side they were attending to; boost in neural processing for attended stimuli over unattended

Question 12

Vialatte et al. wanted to know how attention is mobilized over a long period of time, and presented Ps with a chess design visual stimulus, switching between the positioning of the white and black squares in a regular pattern (counter-phasing). What was the response, and how was it measured?

Answer 12

The brain gave a rhythmical response to onset and offset of stimuli; depending on the frequency of the visual, the brain will tag the rate; Measured by Steady-State-Visual-Evoked Potential (SSVEP)

Question 13

What purpose does the Fast Fourier Transform (FFT) serve, and what did it show in the SSVEP study?

Answer 13

It transforms the SSVEP analysis to find where the most powerful signal is according to frequency; the brain’s fastest response was at every 10hz

Question 14

In a feature-based attention task by Anderson and Muller, Ps were told to either attend to red or blue flickering dots, and determine the direction of motion in which they were moving once coherent. What was found in the FFT analysis?

Answer 14

A larger response at 11.98hz when attending to red dots and at 16.77hz when attending to blue dots; the attended feature gives the brain response a boost (turns up the volume); red is only higher as smaller frequencies tend to give a bigger response than larger frequencies

Question 15

What ratios are measured in fMRI scans, and how long does it take for a BOLD signal to respond?

Answer 15

Ratio of oxyhaemoglobin (diamagnetic) to deoxyhaemoglobin (paramagnetic) serves as a proxy for neural activity; takes around 4 secs

Question 16

In Lui et al.’s fMRI study of automatic spatial attention, a white horizontal bar was flashed to the right or left of fixation, then when two grated circles appeared on each side, Ps had to determine which gratings were slightly tilted off vertical. When was performance better, and which brain region showed the most activation?

Answer 16

When the cue and target appeared at the same location (valid trials); most activation in V4, but validly cued targets also sat higher than others in V3. 2 and 1 (respectively)

Question 17

In Martinez et al.s study of voluntary spatial attention, Ps were told in 50% of trials a doughnut shaped grating would appear around fixation point, and they had to report whether it was present or absent. What did fMRI scans show?

Answer 17

A greater BOLD response in V1 when the target was present, but only slightly smaller when absent, suggesting anticipation is enough to increase activation; Ps who performed better on the task also showed more activity (preparatory response)

Question 18

Transcranial Magnetic Stimulation (TMS) exploits the principle of electromagnetic induction. A stimulating coil generates a magnetic field that passes unimpeded through the skull to induce a secondary electric current in the underlying cortex. What is TMS a useful tool for?

Answer 18

It depolarizes neurons; can suppress/enhance suppression, elicit phosphenes, alter cortical excitability; and is useful for studying localization of brain function and neural connectivity (causal links)

Question 19

Chambers et al. conducted an automatic spatial attention task, cueing Ps to one side of fixation, then telling them to determine which of the two targets presented contained finer gratings (compared to wide), followed by a TMS pulse (at one of 12 times after target onset) in the parietal lobe. What was found?

Answer 19

Right angular gyrus (AG) was the only area that showed impairment at shifting attention, and there were two distinct points in time where performance was much worse (90-100ms; 210-240ms)

Question 20

In Chambers et al.’s study, the different time points in which attention was disrupted appears to be due to two independent visual pathways into the ventral parietal region (right AG). Compare these pathways

Answer 20

Fast retinotectal pathway travels via superior colliculus and pulvinar nucleus to the IPL (crude signal to disengage – only 2 locations to pass); slow geniculostriate pathway travels via LGN, V1, 2, 3, 4, MT, MST to IPL (involves more complex discrimination; many more synapses before reaching destination)

Question 21

Patients with unilateral spatial neglect behave as if the affected side of space (contralesional side) has ceased to exist. Damage to which region is more common and severe?

Answer 21

Right AG in parietal lobe (usually right side); but can arise from cortical damage elsewhere

Question 22

What did Fruhmann-Berger and Karnath find when instructing unilateral spatial neglect patients to look straight ahead?

Answer 22

Head/eye gaze was oriented to the right (even more so for spontaneous orienting)

Question 23

Describe spatial extinction, and how this shows unilateral spatial neglect (even when in recovery) is a pure attention deficit rather than sensory loss

Answer 23

When an experimenter wiggles their fingers only to the left visual field (processed in RH) they can detect it, but if they wiggle fingers simultaneously on left and right, they will only detect those on the right; competition for attention extinguishes awareness on left

Question 24

Posner et al. had patients who had recovered from a stroke but still show extinction press a button when a target appears on the left or right after a valid or invalid cue. What was found?

Answer 24

They were really slow to detect left target but only when not cued for it

Question 25

Eramudugolla et al. compared gradient responses in an auditory and visual spatial search between neglect and non-neglect Ps (hearing tones or detecting targets at different points in space). Compare their performances

Answer 25

Controls were faster for visual stimuli with little variance between left and right; Neglect patients showed much slower RTs for both senses at extreme left (worse for visual), improved at proximal points, and fastest at extreme right; suggests a gradient in deficit

Question 26

How did Haines et al. show effects of inattentional blindness (IB) in the real world?

Answer 26

They had pilots in an aircraft simulator monitor altitude, etc on a screen whilst landing, and failed to see an unexpected stimulus (another aircraft) obstructing the runway

Question 27

Mack and Rock presented Ps with a cross, and they had to decide which limb was longer (trials types consisted of inattention, divided or full attention). What occurred when they introduced another stimulus near the cross?

Answer 27

They would miss it (IB in 25% of trials), but would see it when anticipating it

Question 28

In Rees et al.’s fMRI study of IB, they presented Ps with a picture and a letter stream superimposed over it, and had to either maintain attention on, and detect repetitions in the picture or letter streams. What happened to brain activity when responding to letter streams with meaning (e.g. clock)?

Answer 28

When attending to letter streams there was a bigger BOLD response when meaningful words appeared rather than random letters (word specific boost) both in left frontal and temporal cortices; no difference between real and nonsense words when attending to pictures (attention is diverted)

Question 29

In a natural scene, local transients normally draw attention to the location of the change, which is readily detected. What happens when a mask appears in between successive glimpses of a scene?

Answer 29

It provides a visual transient signal across the whole of the scene, which overrides local transients associated with the change (inducing change blindness)

Question 30

In an fMRI study of change blindness, Beck et al. compared neural activity for detected vs. undetected changes. Items were either faces or places (which changed or didn’t change), presented during an attentional task where Ps had to detect whether an X appeared in either of 2 letter streams. What was found?

Answer 30

Cortical specialization for faces in FFA and places in parahippocampal place area during change detection; 48% correct detection of change for faces, and 53% for places; in attention task: X was detected correctly 95% of the time, with 1.4% false alarms

Question 31

What are mechanisms of attention crucial for?

Answer 31

Enhancing neural representations of behaviourally relevant sensory inputs, and for suppressing representations of irrelevant inputs

Question 32

What does attention alter responses of?

Answer 32

Individual neurons across many levels of cortical representation

Question 33

What have human imaging and stimulation studies revealed about automatic and voluntary shifts in attention?

Answer 33

The locations and time-course of brain activity associated with these

Question 34

Focused attention seems necessary for perceptual awareness. Without it, what happens?

Answer 34

Conscious perception and corresponding neural responses are absent