Active vision Flashcards
What is meant by passive vision?
Vision in the absence of eye movement
What are the underlying assumptions of psychophysics?
There is a threshold below which no sensation present
Orderly relationship between stimulus intensity and sensation level
What did Posner do?
Used precueing to determine whether attention to a specific location improves the ability to respond rapidly to a stimulus presented at that location
What types of cues did Posner use?
Central - Fixate on the central spot and see an arrow that shifts covert attention to the expected side
Peripheral - luminance in peripheral vision leading to automatic shift of covert attention
What was Posner’s spotlight metaphor?
Visual attention like a spotlight traversing the visual field and illuminating regions of interest (all while eyes fixated on one spot)
The spotlight is our covert attention
What is the difference between endogenous and exogenous attention?
Endo = attention generated voluntarily e.g. by the central cues Exo = attention "captured" by peripheral visual events
Why is action of covert attention important?
Speeds simple reaction times and improves perceptual discrimination ability
What is inattentional blindness?
Failure to perceive a stimulus right in full view simply because it is not attended to
What is the distinction between saccades and fixations?
Saccades are accurate and high velocity eye movements
Fixations are when the eye is very still but small movements can occur e.g. tremor, drift and microsaccade
How do we get the impression of the world around us being a continuous scene?
Collect series of visually detailed “snapshots” in a visual scene and the brain combines these into a whole image
What was the case of AI?
Gilchrist, Brown an Findlay
Girl unable to make eye movements but used her head movement in exactly the same way (just a few seconds slower)
What did Gilchrist and Findlay suggest in 2003 regarding covert attention?
Covert attention shifts are slow
Covert sequential scanning doesn’t normally occur during fixations
Covert attention shifts can programme eye movements though
What eye movements are involved prior to performing an action?
Location - find the object to use
Direction - fixate on the object
Guide - bring 2 objects together
Check
What is a real-life important example of coordinating vision and action?
Driving around a corner - we focus on the tangent point on the inside of the road curve
Implications for positioning road signs
What is change blindness?
Failure to notice appearance/disappearance of something when separated scenes using black mask - this is a capacity limitation rather than a visual limitation
What is meant by inhibition of return?
Processing cost in terms of reaction time with returning to a non-cued location - spotlight has already shifted elsewhere
What does visual search involve?
Combination of bottom-up (perceptual) searching and top-down (goal-driven, target in mind to match to)
What is meant by object-based non-spatial attention?
2 objects transparently superimposed in same place
Attended object linked to greater BOLD response in brain region specialised to respond to that particular type of visual stimulus
2 different brain areas activated even though objects in same location
What is the attentional blink?
Inability to report target if appears too soon after initial stimulus because initial stimulus takes over limited attentional capacity
What 4 characteristics determine our fixations?
Stimulus saliency, knowledge about scenes (which affects expectations), nature of task, and learning from experience (where should we look for something)
What findings followed on from Posner’s research?
When attention is directed to an object, the enhancing effect of attention spreads through the object e.g. if cue top of an object, but target appears at bottom responses faster than if target appears in separate adjacent object
Effect remains even if initial shape partially obscured - still perceive it as a whole object
What did Carrasco suggest regarding attention’s enhancing capabilities?
Able to enhance appearance of an object and alter our perception - difference in contrast between gratings
If identical but one preceded by attention-capturing dot, perceive that one as higher contrast and most visible
Distinguish between pre-attentive processing, covert and overt attention
Pre-attentive processing = parallel processing regardless of attentional resources
Overt attention = high resolution, at eye fixation. Covert attention = may be in a different location to eye fixation, cued endogenously/exogenously (slow, covert sequential scanning does not normally occur during fixations, and shifts are linked to eye movements)
