Attention- Brandt Flashcards
where does visual processing start? which cells are involved in visual processing in this structure?
visual processing starts in the retina. processing is done by retinal ganglion cells:
- M cells- 10% of ganglion cells, large receptive fields with small spatial resolution but high temporal resolution. these cells are colour blind but have high contrast.
- P cells- 80% of the cells small receptive fields high spatial resolution but small temporal resolution. they are colour sensitive but have very low contrast.
- gamma cells- 10% of cells. heterogenous cells
where does the visual signal projected to (from the retinal ganglion cells)?
from retinal ganglion cells:
- SCN - records only light and dark, very important for circadian rhythms (tells the brain if it’s day or night)
- -> from SCN: - 10% of SCN fibres go to colliculus superior (fixation of the fovea on the object
- 90% of SCN fibres project to LGN and organised in layers. sorting is based on function and origin of the signal (left/right eye)
- from LGN- primary visual cortex (V1); retinotopic representation of the environment; organisation is in columns and layers
- from V1–>V2–>V3 and 4–> V5
definition of attention
- taking possession by the mind of 1 out of what seems like several simultaneous possible objects or trains of thoughts.
- focalisation, concentration and consciousness are of its essence.
- withdrawal from other things in order to deal efficiently with others.
how many sensory cells and how many axons travel from the retina to the cortex?
10^8 cells and 10^6 axons
what did helnholtz find in his experiment of covert attention?
experiment:
- electrical spark randomly and briefly illuminate parts of a screen.
- fixed gaze (no eye movement)
- moves attention towards objects in the region of the spark
finding:
attention could be deployed independently of eye position and accommodation
–>attention is not always aligned with the visual system
what is Posner’s cue validity task?
experiment:
- computer screen with 2 boxes (left and right)
- subjects were presented either a central (endogenous - arrow to the left or right) or peripheral (exogenous- highlights the box) cue prior to the appearance of a target.
- stimulus (target): valid- stimulus appears on the same side as the cue pointed; invalid- stimulus on opposite box
- parameter: reaction time (subject presses a lever on the side of the stimulus)
finding:
reaction time is much faster when cues were valid!
definition of the feature integration theory?
- there are 2 states of attention:
1. preattentive state- detecting visual components like colour, motion, depth etc.
2. focused attention- integration of the features from satge 1 in parietal lobe: map of location–>attentional spotlight–>object perception
–> in stage 2 the components of vision are integrated and stored in files w. association and combination with different aspects of perception.
people with Ballen syndrome…
a. have lesions in the parietal lobe, and are not able to integrate and combine different aspects of object - problem in focused attention stage
b. have lesions in the occipital lobe, and are not able to register visual aspects of objects like colour and motion - problem in preattentive stage
c. cannot write but can read
d. are blind
a
define the zoom lens model of visual attention. How does it differ from the spotlight of attention model?
- the zoom lens model states that the attended region can be adjusted in size. I.e. attended region size can be allocated according to interest, task demands, or other factors.
- The spotlight model of attention specifies a fixed size for the focal attention zone, that can be moved around under voluntary control. in contrast, the zoom-lens model considers it to be malleable, able to be constricted into a highly focused beam (subtending as little as a fraction of a degree of angle) or dilated to even distribution over the entire visual field.
- according to this model, because of limited processing capacities, there is a tradeoff between size adjustment and detail/processing: An increase in the area attended results in a decrease in the resolution of detail about stimuli within that area.
how could scientists prove the zoom lens model?
task: subjects had to react to differently sized stimuli (stimulus focused on a small area or was more sporadic)
result: subjects reached much faster when attention focus was small.
–> then: fMRI recording of the activity while doing the task–> neural activity in visual areas inversely correlated with attention focus size (big response to small focus and vice versa)
what is the difference between apperceptive agnosia and associative agnosia?
apperceptive agnosia- bilateral lesions in V1, patient can’t perceive observed objects
associative agnosia- patient can’t recognise objects, despite intact perception; bilateral lesions in temporal lobe
what is achromatopsia?
complete inability to see color due to bilateral or unilateral lesions in the temporal cortex.
what is prosopagnosia?
inability to recognise face due to bilateral or right hemisphere lesions.
what is akinotopsia ?
person cannot objectively perceive objects due to lesions in the medial temporal gyrus
what are the dimensions of attentions and what are the components of each dimension? which paradigms are used to test these components?
- intensity:
a. alertness - simple reaction task with or w/o tone
b. sustained attention- high longitudinal signal detection
c. vigilance- low longitudinal signal detection - selectivity:
a. selective attention- choice between targets with distractors
b. visual-spatial selective attention/shifting of attention- task for shifting attention focus
c. divided attention- dual tasks
