Attention Flashcards
What are the two key aspects of attention, and what do they refer to?
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)
In what way are capacity limitation and selectivity two sides of the same coin?
Because we have a limited capacity, we have to be selective
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?
There’s no unique feature (colour/orientation) of the target; have to combine both components so it takes longer
Which neural areas are particularly important for attention processing?
Parietal cortex and lateral PFC
What does the inferotemporal cortex respond to?
Complex features, such as faces
Describe two important features of the primate visual system
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)
What are two distinguishing features of neuronal receptive fields?
Variable size (smaller receptive fields in V1, which get larger further up the hierarchy); and each have different preferred stimuli
Parietal neurons in which region of monkey brains have been implicated in modulating attention during attentional tasks?
Lateral intraparietal (LIP)
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)
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
Which area of the visual cortex contains neurons with large receptive fields that are tuned to colour and shape?
V4
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)?
When the stimulus appears on the side they were attending to; boost in neural processing for attended stimuli over unattended
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?
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)
What purpose does the Fast Fourier Transform (FFT) serve, and what did it show in the SSVEP study?
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
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?
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
What ratios are measured in fMRI scans, and how long does it take for a BOLD signal to respond?
Ratio of oxyhaemoglobin (diamagnetic) to deoxyhaemoglobin (paramagnetic) serves as a proxy for neural activity; takes around 4 secs
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?
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)
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?
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)
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?
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)
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?
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)
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
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)
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?
Right AG in parietal lobe (usually right side); but can arise from cortical damage elsewhere
What did Fruhmann-Berger and Karnath find when instructing unilateral spatial neglect patients to look straight ahead?
Head/eye gaze was oriented to the right (even more so for spontaneous orienting)
Describe spatial extinction, and how this shows unilateral spatial neglect (even when in recovery) is a pure attention deficit rather than sensory loss
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
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?
They were really slow to detect left target but only when not cued for it
