lecture 5 Flashcards
(25 cards)
Describe direct perception
– What we perceive about the world is directly available in the stimulus
– For example, optical flow: changes in retinal image as observer moves gives cues to location, distance etc.
– (Almost) all perception becomes motion perception
what is the optic array
the pattern of light reaching the eye
what is the optic low / focus of expansion
- Optic flow field as a pilot comes in to land, with the focus of expansion in the middle (from Gibson, 1950)
- Focus of expansion: Only point which does not appear to move as the observer moves
describe outflow(optical flow pattern)
Forward movement:
Outflow from point of expansion
landing a plane
describe inflow (optical flow pattern)
Backward movement:
Inflow from point of expansion
view from the back of a train
what are invariants
Higher-order characteristics of the visual array
that are unaltered by movement
describe information processing approach
– Perception involves stages of information processing
– What are the units of information that the senses
extract from the stimulus?
– How are these units combined with knowledge from
prior experience?
what are affordances
- Potential uses of objects (NB perception-for-action system)
- Action opportunities are perceived directly
- Can help to categorize objects in terms of their use rather than in terms of their features
describe weakness of direct perception
Processes involved in perception are much more complicated than implied by Gibson
• Also predated “embodied
• The failure to assume the
existence of internal representations to understand
perception is seriously flawed
• Underestimated the importance of top-down processes
• Largely ignored the vision for perception system (the ventral pathway
describe strengths of direct perception
- Noted the importance of changes in the optic array
- Captured the dorsal, vision-foraction system before it became important in other theories (e.g. that of Milner & Goodale)
describe the radial outflow hypothesis
The overall outflow pattern specifies an observer’s heading
– Works well for linear movement, but not for non linear movement
• Retinal flow field (changes in the pattern of light on the retina), determined by:
– Linear flow containing a focus of expansion
– But also rotary flow (rotation in the retinal image)
produced by following a curved path and by eye and
head movements
describe future path strategy
Active gaze down predicted future path
describe tangent point strategy
– The point on the road where the direction of the inside edge appears to reverse
– Curvature computed from the angle between heading and tangent point
describe tau alternative
– The size of an object’s retinal image divided by its rate of expansion
– Assumes velocity is constant
– Specifies time to contact
• Faster expansion = less time
describe strength of tau
• The tau hypothesis is appealingly simple
• Tau is often used to assist in making decisions about time to Limitations
• Tau can be computed based on variables measured
directly from the eye
describe weakness of tau
• Tresilian (1999)
– Only works with objects of constant velocity; ignores
acceleration of object contact
– Only provides information about time to contact of eyes
– Objects need to be spherically symmetrical
which regions involved in perception of biological motion
– The Superior Temporal Sulcus (STS) and ventral PreMotor cortex (vPMC)
describe limitations of biological motion
• Relatively little is known about how bottom-up and top-down processes interact
• The shared and differential components of biological and non-biological motion processing are not well
understood
describe strengths of biological motion
- An impressive ability
- Specific brain regions
- Patient studies indicate that biological motion is processed differently to non-biological motion
describe the monkey research
– Neurons activated when
• Regions that respond similarly animals perform an action and when they observe another performing the
same action
– Area F5 in premotor cortex
(Gallese et al., 1996)
– Facilitates imitation and understanding others’ actions
• Neurons fire when intention is the same, not when the action is the same (Umiltà et al., 2001)
describe inattentional blindness
The failure to notice an unexpected but fully visible
item when attention is diverted to other aspects of a
display
describe change blindness
The surprising failure to detect a substantial visual
change
What causes change blindness
(a) Fixation before change is required for accurate detection
(b) Attention to the to-be-changed object is necessary but not sufficient for change detection
(c) Change detection better for type changes (e.g. plate replaced by bowl) than for token changes (e.g. plate replaced by another plate)
(d) No systematic effect of number of intervening fixations (memory effect)
what are the strength of mirror neurons theory
Evidence of a mirror neuron system in monkeys and humans
• (Implicit) imitation of perceived actions can play a role in interpreting the intentions behind the actions
– Similar to old idea of “analysis by synthesis“
