Cognitive Neuroscience - Attention and Perception Flashcards
What is visual agnosia?
Can see objects but cannot identify them - unable to connect visual information with knowledge of things ie cannot differentiate between a square and a rectangle
Deficit in the ventral stream/temporal lobe, can’t understand ‘what’ is perceived; also links to memory function
No deficit in the dorsal stream, can understand the action component of perception, the ‘where’ (special locations)
How did Milner and Goodale (2008) describe the functions of the ventral and dorsal streams?
Ventral - abstract representation of the world; can be stored for future reference - visual memory - and allows us to organise the information in the world and plan future actions
Dorsal - acts in real time to guide actions and enable smooth and effective movements
Dorsal + ventral streams - when actions involve use of memory; planning is required and there is time is available for planning; the action is unpractised/awkward
Whats the relationship between attention and perception?
Covert shifts of attention (voluntary/involuntary) affect the perceptual processing of targets at both attended and non attended locations - ‘top down’ processing ie higher level process influences lower level process
The stage at which attention operates is dependent on the location of ‘overload’ in processing ie under heavy perceptual demands - locus of selection at the level of perceptual processing; when under less perceptual demand, attention modulates at a higher level - attention is a finite computational resource
What is an attentional blink?
Inability to respond to a second target when presented very soon after the first one
What are the basics behind interpreting ERPs?
Series of positive and negative deflections, each representing different aspects of cognitive processing - if a task variation changes deflections - can see that processing is changing
What do ERPs look like for attentional blinks?
Early visual components (P1+N1) - dont change according to lag (time between 1st/2nd stimulus presentation)
Later ERP component P3 - abolished with lag and probability of reporting 2nd stimulus was low
P3 may reflect processes involving maintaining/updating working memory; its absence under lag conditions reflects the view that rapid presentation of stimuli increases demands on WM and causes the loss of some info
Why might invalid stimuli on the posner cuing task be responded to less quickly?
Stimuli fall outside the spotlight of attention - perceived less well ie attention influences perception
When a cue is presented, subjects prepare to makea response with the hand they would use if the cue was valid - the RT benefit for valid trials is due to motor priming and attention does not influence perception
(not mutually exclusive either)
What are typical ERP findings on Posner cuing tasks?
Smaller N1 and P1 - both thought to reflect perceptual processing - when target appears in invalid location
P1 = extrastriate cortex (V3-5); larger the P1 amplitude, the faster the RT - excitatory and inhibitory effects are due to changes in perception of the stimuli
In visual processing areas, objects falling inside/outside the spotlight of attention are not processed equivalently - high level process modulating low level
But both voluntary and involuntary forms of attention influence perception and appear to operate similarly
What are preparatory processes?
Analogy - preparing to catch a tennis ball vs a medicine ball - better to adopt a different stance because of expectations
Cognitive tasks: prepare differently depending on what stimulus you expect to encounter (ie left vs right visual field); prepare differently depending on what you have to do with the information (ie press a key, speak aloud
What is the difference between stimulus and task related activity?
Task = starts when task does and continues (and changes, more slowly) throughout - can be monitored with haemodynamic measures
Item/stimulus = starts when a test stimulus is presented and finishes before the next is presented
What does ERP data suggest about the relationship between attention and V1 activation?
C1 occurs before P1/N1 complex - is not influenced by attention and is generated in V1 - suggesting V1 is not influenced by attention
What does fMRI data suggest about the relationship between attention and V1 activation?
Sommers et al 1999
Attend to either - direction of motion at periphery of a screen, letters in the centre or simply passive viewing
Data showed increased blood flow in areas of V1 corresponding to periphery, attention reduces activity at unattended locations - attention does impact V1 activation
Why is there a difference between the ERP and fMRI data concerning attention and V1 activation?
Maybe…
Sensitivity of ERPs to attention changes as indexed by C1? Blood flow more sensitive?
Different tasks in ERP/fMRI - is more task more sensitive?
What did Martinez et al (1999) study concerning attention and V1?
Used same measures in ERP/fMRI - discrimination task - detect targets only in attended visual field; blocked design with attending L then R
Greater contralateral V1 activation when attending to stimuli but not reflected in C1 modulation
What is source localisation?
Computational ERP technique to identify the most likely region responsible for activity detected on the scalp
Dipole modelling is an example
